Evaluating Tomato-Potato Heterografting for Enhanced Crop Performance in Sri Lanka

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Perera, K.M.R.D. Abhayapala, P.N.M.S. Piyarathne, S.M.C.M Samarakoon, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9199706/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract This study systematically evaluated the agronomic viability of a novel double-cropping system through heterografting between tomato ( Solanum lycopersicum L.) and potato ( Solanum tuberosum L.). Using cleft grafting, two determinate tomato scions ( Thilin a and Padma ) were grafted onto the vigorous potato rootstock Granola under protected cultivation in Sri Lanka's up-country region. Results demonstrated a critical scion-specific interaction governing system productivity. The Granola/ Padma combination exhibited a greater compatibility, increasing tomato fruit yield by 2.8-fold and potato tuber yield by 2.1-fold per plant compared to non-grafted controls. Yield enhancement was exclusively mediated through a significant increase in the number of fruits and tubers, not their individual size. In contrast, the Granola/ Thilina graft increased tomato yield but suppressed tuber initiation, highlighting a competitive interaction. Heterografting modified plant architecture, reducing height by 21–24% while maintaining or enhancing leaf area, and caused only minor, agronomically insignificant delays in phenology with no detriment to fruit quality. These findings confirm that interspecific grafting within Solanaceae is a functionally viable intensification strategy. The synergistic Granola/ Padma graft establishes a scientifically validated model for dramatic land-use efficiency gains, leveraging complementary resource partitioning and source-sink balance to optimize productivity from a single plant, with direct applicability for smallholder systems. Double-cropping Heterografting Land-use efficiency Protected cultivation Solanum lycopersicum Solanum tuberosum Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Global agricultural systems face the dual imperative of intensifying food production to meet the demands of a growing population while adapting to the constraints of limited arable land and climate variability (FAO 2017 ). This challenge is particularly acute for vegetable cultivation, a vital source of nutrition and income for smallholder farmers. In regions like Sri Lanka, production of high-value solanaceous crops such as tomato ( Solanum lycopersicum L.) and potato ( Solanum tuberosum L.) is often hampered by persistent challenges. Potato cultivation, for instance, is severely impacted by soil-borne diseases like bacterial wilt ( Ralstonia solanacearum ) and late blight ( Phytophthora infestans ), which can cause devastating yield losses (Pandey et al. 2017 ; Chandrasena et al. 2020 ). Similarly, tomato production is frequently constrained by the same soil-borne pathogens, as well as root-knot nematodes ( Meloidogyne spp.), leading to significant annual deficits (Prematilake et al. 2018 ). Vegetable grafting has emerged as a pivotal horticultural technology to mitigate these production constraints. By surgically joining a desirable scion cultivar to a vigorous, stress-resistant rootstock, grafting can enhance plant vigor, increase yield, and improve tolerance to environmental stresses and soil pathogens (Savvas et al. 2010 ; Kyriacou et al. 2017 ). The use of resistant rootstocks is considered a key component of integrated pest management and a sustainable alternative to soil fumigation (Singh et al. 2017 ). While homografting (within the same species) is common, heterografting between different species within the same family offers a unique opportunity to combine complementary traits. For instance, grafting tomato onto disease-resistant eggplant rootstocks is a proven strategy to manage bacterial wilt (Gisbert et al. 2011 ). However, the practical application of grafting in many developing agricultural contexts remains limited by access to specialized rootstock seed and technical knowledge. Tomato and potato, both members of the Solanaceae family, are prime candidates for heterografting. They share sufficient genetic proximity for graft compatibility while offering distinct and potentially synergistic advantages. The potato plant is known for its robust and extensive root system, which is highly efficient at water and nutrient uptake (Wishart et al. 2013 ). Utilizing potato as a rootstock could theoretically provide a stronger foundation for a tomato scion, potentially enhancing its resilience and productivity. Conceptually, a successful heterografted plant could yield both tomato fruits from the scion and potato tubers from the rootstock, thereby maximizing land productivity, a concept of significant value for space-limited cultivation systems and home gardens (Obrero et al. 2020 ). This "double-cropping" approach from a single plant has the potential to improve land use efficiency substantially. Despite this compelling potential, research on tomato-potato heterografting remains sparse and inconsistent. Existing studies are often anecdotal or lack rigorous agronomic and physiological evaluation under controlled conditions. Key questions regarding the optimal grafting technique, the impact on the phenology and yield dynamics of both components, and the underlying physiological mechanisms of resource partitioning remain largely unanswered. For example, the influence of a fruiting tomato scion on the tuberization signals and sink strength of a potato rootstock is not well understood (Fernie and Bachem 2021 ). This knowledge gap hinders the development of this technique as a reliable, science-based practice for growers. Therefore, this study was designed to systematically evaluate the viability and agronomic performance of heterografting commercially important tomato varieties ( Thilina and Padma ) onto a potato (Granola) rootstock under the protected cultivation system of Sri Lanka's up-country region. The specific objectives were to: (1) assess the success rate of cleft grafting between tomato scions and potato rootstocks; (2) evaluate the effects of heterografting on the growth, yield, and phenology of the tomato scion; and (3) determine the impact of the tomato scion on the tuber yield and quality of the potato rootstock 2. Materials and Methods 2.1. Experimental Site and Growing Conditions The study was conducted from May to December 2024 in a polyethylene-covered polytunnel at the Agriculture Research and Development Centre, Sita-Eliya, Nuwara-Eliya, Sri Lanka (6°58'N, 80°46'E, altitude 1860 m above mean sea level). This location is within a major potato and temperate vegetable growing region characterized by a humid subtropical highland climate. The polytunnel environment was maintained to mitigate excessive rainfall and temperature fluctuations, with average daily temperatures ranging from 15°C to 22°C and natural photoperiod throughout the trial. 2.2. Plant Materials and Cultivation Two tomato ( S. lycopersicum L.) varieties, Thilina (indeterminate vine habit) and Padma (determinate bush habit), were used as scions. The potato ( S. tuberosum L.) cultivar Granola was selected as the rootstock for its regional adaptability and vigorous growth. A sterile, well-draining substrate was prepared by mixing burnt paddy husk and composted tea waste (1:1 v/v), which was subsequently steam-sterilized at 100°C for 8 hours. Tomato seeds were sown directly into 15 cm diameter pots filled with this substrate. Certified disease-free Granola seed tubers were planted individually in separate pots to develop rootstock plants. All plants were irrigated using a drip system and fertilized weekly with a standard Albert solution (2 g L⁻¹) as per the recommendation of the Department of Agriculture, Sri Lanka. 2.3. Grafting Technique and Healing Management Cleft grafting was performed 30 days after planting (DAP), when both scion and rootstock stems attained a uniform diameter of 4.0 ± 0.5 mm. The rootstock was decapitated horizontally, and a vertical incision (1.5–2.0 cm deep) was made in the center of the stump. A matching scion, excised from the tomato seedling to include 2–3 fully expanded leaves, was shaped into a wedge. The scion was inserted into the rootstock cleft, ensuring firm cambial contact on at least one side. The graft union was secured immediately with a biodegradable grafting clip. To promote healing, each grafted plant was covered with a transparent polyethylene bag to maintain high relative humidity (> 90%) for 14 days. The bags were removed after confirming successful union, indicated by scion turgidity and new leaf growth. 2.4. Experimental Design and Treatments The experiment was arranged in a Complete Randomized Design (CRD) with ten replications per treatment. The five treatments were: Non-grafted potato Granola (rootstock control) Non-grafted tomato Thilina (scion control) Non-grafted tomato Padma (scion control) Heterograft of Granola (rootstock) and Thilina (scion) Heterograft of Granola (rootstock) and Padma (scion) All plants were individually potted and spaced at 50 × 50 cm. Standard integrated pest management practices were followed. A fungicide (cymoxanil 8% + mancozeb 64%) was applied three times as a preventive spray against late blight ( Phytophthora infestans ). 2.5. Data Collection Data were collected on growth, phenology, and yield components. Growth Parameters: Plant height (from soil surface to the apical meristem) and total leaf number were recorded from eight randomly selected plants per treatment at 14-day intervals, commencing 14 days after grafting. Phenological Parameters: The number of days from planting to 50% flowering, 50% fruit set, and first harvestable fruit (at 50% surface ripening) was recorded for tomato. Yield and Yield Components (at physiological maturity): Tomato: Total number of fruits per plant, mean individual fruit weight (g), and total fruit yield per plant (g). Potato: Total number of tubers per plant (diameter ≥ 2.5 cm), mean individual tuber weight (g), and total tuber yield per plant (g). Harvest occurred at 120 DAP, corresponding to full vine senescence. 2.6. Statistical Analysis All collected data were subjected to Analysis of Variance (ANOVA) using Minitab Statistical Software (Version 18.0). The significance of treatment means was tested using Fisher’s Least Significant Difference (LSD) test at a 5% probability level (p ≤ 0.05). Relationships between key yield components (e.g., fruit number vs. yield) were examined using Pearson’s correlation analysis. Data are presented as mean ± standard error (SE). 3. Results and Discussion 3.1. Growth Performance of Grafted and Non-Grafted Tomato Plants The heterografting of tomato scions onto potato rootstock induced significant and consistent modifications to the vegetative growth architecture of the tomato component. Analysis of the longitudinal dataset for plant height and total leaf number revealed a clear physiological pattern: grafted plants developed a more compact architecture while maintaining, or even enhancing, their foliar capacity compared to non-grafted controls. This dissociation between vertical extension and leaf production highlights a distinct rootstock-mediated regulation of growth. A significant main effect of treatment was observed for final plant height (p < 0.05). Grafted plants exhibited a pronounced reduction in vertical growth. Non-grafted Tomato ( Padma ) and Non-grafted Tomato ( Thilina ) controls reached average final heights of 113.03 cm and 103.16 cm, respectively. In contrast, their grafted counterparts, Granola /Padma and Granola/ Thilina , attained significantly lower average heights of 86.47 cm and 81.43 cm (Table 1 ). This represents a substantial reduction of approximately 23.5% for grafted Granola /Padma and 21.1% for grafted Granola/ Thilina plants. The plant height curves in Fig. 1a illustrate that this suppression was not merely a final outcome but a consistent trend, with the growth trajectories of grafted plants diverging from controls early in development and maintaining a lower slope throughout. In stark contrast to height, the final total leaf number was not adversely affected by grafting. No significant differences (p > 0.05) were found between grafted and non-grafted Padma plants, with averages of 124.8 and 124.0 leaves, respectively (Table 1 ). Notably, grafted Granola/ Thilina plants supported a significantly greater final leaf number (236.0) compared to non-grafted T plants (173.2). The curves showing number of leaves in Fig. 1b show that while the Padma varieties maintained parallel trajectories, the grafted Granola/ Thilina combination consistently produced more leaves than its non-grafted control from the early stages, indicating a sustained enhancement in leaf initiation or retention. Table 1 Final growth parameters of grafted and non-grafted tomato plants at the last measurement interval Description Avg. final height (cm) ± SE Avg. final leaf no. ± SE Non-grafted Tomato ( Padma ) 113.03 ± 4.24 a 124.0 ± 12.7 b Non-grafted Tomato ( Thilina ) 103.16 ± 3.89 a 173.2 ± 15.9 c Grafted Granola/ Padma 86.47 ± 3.21 b 124.8 ± 13.1 b Grafted Granola/ Thilina 81.43 ± 3.05 b 236.0 ± 18.3 a Means within a column followed by different letters are significantly different according to Fisher's LSD test (p ≤ 0.05). SE = Standard Error. Data are from the final recorded measurement for each surviving plant (n=7–10). The observed growth modulation, significant height reduction without a compromise in leaf number is a classic manifestation of rootstock-scion interaction, aligning with established grafting physiology (Goldschmidt 2014 ). The compact stature of grafted plants likely results from altered hormonal signaling, particularly in gibberellin pathways, which are known to be transmitted across the graft union and regulate internode elongation. This dwarfing effect is not indicative of poor vigor but rather a reallocation of resources. The maintenance or increase in leaf number, as clearly seen in the grafted Granola/ Thilina combination, confirms that the photosynthetic source capacity is preserved or enhanced. This architectural change has critical agronomic implications. A plant with reduced height but undiminished leaf area represents a more efficient, compact growth habit. It can improve light distribution within the canopy, reduce mutual shading, lower the risk of lodging, and facilitate management practices in protected cultivation systems like polytunnels (Singh et al. 2017 ). Importantly, this structure suggests an optimization where resources may be diverted from supporting excessive vegetative framework (stems) towards productive sinks namely, fruits and tubers. The robust potato rootstock (Granola), known for a vigorous root system (Wishart et al. 2013 ), appears to support a prolific leaf canopy while simultaneously exerting a regulatory effect on scion height, creating an ideal morphology for a dual-cropping system aimed at maximizing yield per unit area. This finding supports the potential of heterografting as a tool not just for stress resistance, but for tailored growth management (Kumar et al. 2017 ; Obrero et al. 2020 ). 3.2. Yield and Yield Components of Tomato Scions Heterografting onto potato rootstock profoundly and significantly enhanced the reproductive performance of tomato scions. The yield advantage was not only substantial in magnitude but also consistent across both scion cultivars, fundamentally altering the productivity profile compared to non-grafted controls. The data reveal that this increase was mechanistically driven by a dramatic improvement in fruit set rather than by enlarging individual fruit size. A summary of the key yield parameters for all tomato-based treatments is presented in Table 2 . The overall impact on total fruit yield, number of fruits, and individual fruit weight are visualized in Fig. 2. 3.2.1 Total Fruit Yield and Fruit Number Heterografting resulted in a transformative increase in total yield (p < 0.05). The Granola /Padma combination was exceptionally productive, with an average yield of 891.49 g per plant. This represents a 2.8-fold increase over the non-grafted Padma control, which yielded 317.71 g per plant. Similarly, the Granola /Thilina graft yielded an average of 546.37 g per plant, a 3.8-fold increase over the non-grafted Thilina yield of 142.45 g (Table 2 ). This remarkable yield enhancement was unequivocally driven by a significant increase in the number of fruits harvested per plant. Grafted plants consistently set and matured more fruits (Fig. 2b). The average fruit number for grafted Granola /Padma plants (20.2) was 2.2 times greater than for P plants (9.0). Grafted Granola/ Thilina plants also produced more than double the fruits (14.8) of non-grafted Thilina plants (5.7) (Table 2 ). Correlation analysis confirmed a very strong positive relationship between total fruit yield and fruit number per plant across all individuals (r = 0.97, p 0.05). The average fruit weight for grafted plants (grafted Granola /Padma : 43.94 g; grafted Granola/ Thilina : 40.08 g) was statistically comparable to that of their non-grafted counterparts (P: 39.71 g; T: 36.18 g) (Table 2 ). Table 2 Yield and yield components of grafted and non-grafted tomato scions Treatment Avg. fruit no. per plant ± SE Avg. individual fruit weight (g) ± SE Avg. total fruit yield per plant (g) ± SE Non-grafted Tomato ( Thilina ) 5.7 ± 1.8 c 36.18 ± 1.5 a 142.45 ± 77.1 c Non-grafted Tomato ( Padma ) 9.0 ± 0.6 b 39.71 ± 4.5 a 317.71 ± 47.2 b Grafted Granola/ Thilina 14.8 ± 1.5 a 40.08 ± 3.2 a 546.37 ± 58.9 a Grafted Granola/ Padma 20.2 ± 1.0 a 43.94 ± 1.9 a 891.49 ± 72.4 a Means within a column followed by different letters are significantly different according to Fisher's LSD test (p ≤ 0.05). SE = Standard Error. Data based on n=5–6 plants per treatment. 3.2.3 Phenology of Harvest The timing of first harvestable fruit was slightly delayed in grafted plants. Non-grafted tomatoes reached first harvest 153 DAP. Grafted Granola/ Thilina and Granola /Padma plants were harvested at 158 DAP and 162 DAP, respectively, indicating a delay of 5–9 days (Table 3 ). This modest delay is likely attributable to the initial resource allocation required for graft union healing and acclimation. Table 3 Days from planting to first harvestable fruit Treatment Planted date Grafted date First harvest date Days after planting (DAP) Non-grafted Tomato ( Thilina ) 2025.05.24 Not Applicable 2025.10.24 153 Non-grafted Tomato ( Padma ) 2025.05.24 Not Applicable 2025.10.24 153 Grafted Granola/ Thilina 2025.05.24 2025.06.24 2025.10.29 158 Grafted Granola/ Padma 2025.05.24 2025.06.24 2025.11.02 162 The results demonstrate that tomato-potato heterografting is a highly effective strategy for yield intensification, primarily through the physiological mechanism of enhanced fruit set. The robust, perennial-like root system of the potato rootstock Granola likely provides superior and more stable access to water and nutrients during critical flowering and fruit-set stages. This mitigates abiotic stress that commonly leads to flower abortion in non-grafted plants, thereby allowing a greater proportion of flowers to develop into mature fruits (Kumar et al. 2017 ; Savvas et al. 2010 ). The finding that individual fruit weight remained unchanged is significant. It indicates that the yield gains were achieved without diluting resources across an excessive number of sinks, which can lead to smaller, unmarketable fruit. Instead, the potato rootstock effectively supported the increased sink demand created by the higher fruit number. This aligns with the concept of rootstock-mediated improvement in overall plant vigor and assimilate supply capacity (Goldschmidt 2014 ). The slight delay in phenology is a negligible trade-off considering the magnitude of yield increase and is common in grafted systems due to the initial recovery phase. The superior performance of the Granola /Padma combination over Granola /Thilina suggests a scion-specific interaction. The determinate growth habit of Padma may synchronize better with the resource partitioning patterns induced by the potato rootstock, leading to more efficient conversion of vegetative resources into reproductive output. This underscores the importance of selecting optimal scion-rootstock combinations to maximize synergism in heterografting systems (Obrero et al. 2020 ; Singh et al. 2017 ). 3.3. Yield and Yield Components of Potato Rootstocks The heterografting system induced a significant and scion-dependent effect on the tuber yield of the potato (Granola) rootstock. This finding demonstrates that the presence and identity of a tomato scion directly influence the reproductive sink activity of the underground rootstock component. The potato's response ranged from yield suppression to significant enhancement, highlighting a complex interplay of resource partitioning and source-sink signaling within the composite plant. Total Tuber Yield and Tuber Number: The total tuber yield per plant was significantly affected by the grafting treatment (p < 0.05). Notably, the effect was not uniform but depended entirely on the grafted tomato scion (Fig. 3a). The Granola/ Padma graft combination resulted in the highest average tuber yield of 324.31 g per plant, which was 1.9 times greater than the yield of the non-grafted Granola control (169.24 g) and significantly higher than all other treatments. In contrast, the Granola/ Thilina combination produced an average yield of only 141.27 g per plant, which was not statistically different from the non-grafted control but represented a clear numerical reduction. This differential response was primarily driven by changes in the number of tubers set per plant (Table 4 ). The grafted Granola /Padma plants produced an average of 8.0 tubers, a significant increase over the non-grafted G average of 7.8 tubers. The grafted Granola/ Thilina plants, however, produced only 3.4 tubers on average, explaining their low total yield. Correlation analysis confirmed a strong positive relationship between total tuber yield and tuber number across all plants (r = 0.88, p < 0.001). Table 4 Yield and yield components of non-grafted and heterografted potato rootstocks Treatment Avg. tuber no. per plant ± SE Avg. individual tuber weight (g) ± SE Avg. total tuber yield per plant (g) ± SE Non-grafted Potato (Granola) 7.8 ± 1.1 ab 37.86 ± 3.8 a 169.24 ± 21.4 b Grafted Granola/ Thilina 3.4 ± 0.7 c 42.73 ± 2.4 a 141.27 ± 24.1 b Grafted Granola/ Padma 8.0 ± 1.2 a 41.09 ± 1.2 a 324.31 ± 47.5 a Means within a column followed by different letters are significantly different according to Fisher's LSD test (p ≤ 0.05). SE = Standard Error. Data based on n=5 plants per treatment for yield/weight; tuber number includes n=6. Individual Tuber Weight: The mean weight of individual tubers was not significantly altered by heterografting (p > 0.05). All treatments produced tubers of statistically equivalent size, with averages ranging from 37.86 g [Non-grafted tomato ( Granola )] to 42.73 g (grafted Granola/ Thilina ) (Table 4 , Fig. 3c). This indicates that the grafting treatments affected the initiation and set of tuber sinks rather than the process of tuber bulking . The resources available to each established tuber remained consistent, regardless of the total number on the plant. The scion-specific yield outcomes for the potato rootstock represent a critical finding with important physiological implications. The enhanced tuber yield in the grafted Granola /Padma combination suggests a synergistic, rather than competitive, relationship between the Padma scion and the Granola rootstock. The highly productive Padma canopy (as shown in Section 3.2 ) likely acted as a powerful source of photo assimilates. A portion of these assimilates may have been translocated to the rootstock, stimulating stolon initiation and tuber set, thereby increasing sink number (Fernie & Bachem 2021 ). This aligns with the concept of graft unions facilitating bidirectional resource and signaling exchange (Goldschmidt 2014 ). Conversely, the lack of yield benefit and even a trend toward suppression, in the grafted Granola/ Thilina combination indicates a competitive interaction. The Thilina scion, while more productive than its non-grafted form, may have been a stronger sink for resources or may have transmitted different hormonal signals that partially inhibited the tuberization process in the potato rootstock. The fact that individual tuber weight was maintained across all treatments suggests that once a tuber is initiated, it becomes a prioritized sink capable of drawing necessary resources, but grafting with Thilina severely limited the initiation event itself. From an applied perspective, this underscores that successful double-cropping via heterografting requires the selection of compatible partners that establish a mutually beneficial or neutral resource-sharing relationship. The Granola/ Padma combination emerges as uniquely proficient, enhancing the yield of both components, tomato fruits and potato tubers, simultaneously. This synergistic effect leverages the robust root system of the potato (Wishart et al., 2013 ) and the high photosynthetic output of the Padma scion to maximize overall land productivity, validating the core premise of this integrated cropping model (Kumar et al. 2017 ; Obrero et al. 2020 ). 3.4. Phenology and Fruit Quality Parameters 3.4.1. Phenological Development The phenological development of the tomato scion was largely unaltered by heterografting onto potato rootstock. Analysis of key reproductive milestones revealed only minor, non-significant delays (Table 5 ). For the Thilina varieties, the time to 50% flowering was identical at 100 DAP for both grafted (Granola/ Thilina ) and non-grafted Thilina plants. The subsequent 50% fruit set occurred at 111 DAP for non-grafted plants and 113 DAP for grafted plants, a negligible 2-day delay. A more pronounced but still modest delay was observed in the Padma varieties, where grafting (Granola /Padma ) postponed 50% flowering by 5 days and 50% fruit set by 8 days compared to the non-grafted Padma control. Consequently, the date of first harvestable fruit was delayed by 5 days for the grafted Granola/ Thilina combination and 9 days for the grafted Granola /Padma combination (Fig. 4 ). These delays are consistent with the typical resource allocation required for graft union healing and re-establishment of vascular flow, a common transient effect in vegetable grafting that does not disrupt crop cycle planning (Kumar et al. 2017 ; Singh et al. 2017 ). Critically, the grafting process did not induce juvenility or reset the developmental program, affirming the physiological compatibility of the heterograft system. Table 5 Phenological development timeline of grafted and non-grafted tomato plants Treatment Days to 50% flowering (DAP) Days to 50% fruit set (DAP) Days to first harvest (DAP) Non-grafted Tomato ( Thilina) 100 111 153 Grafted Granola /Thilina 100 113 (+ 2) 158 (+ 5) Non-grafted Tomato ( Padma ) 78 96 153 Grafted Granola /Padma 83 (+ 5) 104 (+ 8) 162 (+ 9) DAP = Days After Planting. Values in parentheses indicate delay relative to non−grafted control. 3.4.2. Fruit Quality Attributes The marketable quality of tomato fruits, assessed through physical dimensions, was preserved or even slightly enhanced by grafting (Table 6 ). There was no significant effect of grafting on fruit diameter for either scion variety. However, a notable and positive trend was observed in fruit morphology. While the characteristic shape of each variety was maintained, Thilina fruits remained round and Padma fruits elongated, the grafted Granola /Padma fruits exhibited a non-significant increase in average length (5.28 cm) compared to their non-grafted counterparts (4.92 cm). This resulted in a preserved length-to-diameter ratio, confirming the maintenance of varietal typicity (Fig. 5 ). The stability of fruit size alongside a dramatic increase in fruit number (Section 3.2 ) indicates that the robust potato rootstock effectively supplied the necessary water and photo assimilates to support the enlarged sink demand without compromising individual fruit development. This aligns with findings that vigorous rootstocks can improve fruit quality by sustaining resource supply during critical growth phases (Gisbert et al. 2011 ; Savvas et al. 2010 ). Table 6 Fruit dimensional quality parameters of grafted and non-grafted tomato plants Treatment Average fruit diameter (cm) ± SE Average fruit length (cm) ± SE Length-to-diameter ratio ± SE Non-grafted Tomato ( Thilina) 4.47 ± 0.10 a 4.10 ± 0.06 b 0.92 ± 0.02 b Grafted Granola /Thilina 4.68 ± 0.09 a 4.24 ± 0.05 b 0.91 ± 0.02 b Non-grafted Tomato ( Padma) 4.44 ± 0.09 a 4.92 ± 0.17 a 1.11 ± 0.04 a Grafted Granola /Padma 4.70 ± 0.06 a 5.28 ± 0.05 a 1.12 ± 0.01 a *Means within a column followed by different letters are significantly different according to Fisher's LSD test (p ≤ 0.05). SE = Standard Error. 3.5. Synthesis and Practical Implications The collective findings of this study provide strong evidence for the agronomic viability and significant productive potential of tomato-potato heterografting as a novel double-cropping system. The results demonstrate that success is not universal but hinges on specific, compatible scion-rootstock combinations. The Granola/ Padma heterograft emerged as uniquely synergistic, delivering a transformative increase in total land productivity. This combination yielded 2.8 times more tomato fruit and 2.1 times more potato tubers per plant than non-grafted counterparts. This dual yield enhancement was primarily driven by a greater number of reproductive sinks, more fruits and tubers rather than an increase in their individual size. This suggests the robust potato rootstock improved the plant's capacity to support reproductive development during critical setting phases, likely through enhanced resource acquisition, while the vigorous Padma scion supplied ample photo assimilates that benefited both its own fruits and the rootstock's tubers. Importantly, this substantial yield gain was achieved with only a minor delay in harvest phenology and no detriment to fruit quality, confirming the technique's practical feasibility. From an applied perspective, this heterografting model offers a powerful strategy for vertical intensification, particularly for smallholders and home gardeners in Sri Lanka and similar regions where arable land is limited. It enables the concurrent production of two nutrient-rich crops from a single planting point, dramatically improving land-use efficiency and household food security without requiring advanced technology or compromising crop marketability. 3.6. Limitations and Future Research While this controlled-environment study provides compelling proof-of-concept for tomato-potato heterografting, several limitations must be acknowledged to contextualize the findings appropriately and guide future inquiry. The experiment was conducted under polytunnel conditions, which buffered against environmental stressors such as variable rainfall, wind, and extreme temperature fluctuations. Consequently, the performance and resilience of these heterografts under open-field conditions exposed to real-world abiotic stresses and full biotic pressure from soil-borne pathogens such as Ralstonia solanacearum remain to be evaluated. The controlled environment may have optimized conditions for graft establishment and resource partitioning, potentially overestimating the performance achievable under typical smallholder cultivation conditions. Furthermore, this study examined only two tomato scion varieties ( Thilina and Padma ) and a single potato rootstock (Granola). While this limited scope allowed detailed characterization, it precludes broad generalization. The starkly contrasting outcomes between the two scion varieties synergistic with Padma versus neutral/competitive with Thilina , underscore that scion-rootstock compatibility is highly specific, and without screening additional cultivars, the optimal combinations for this system remain largely unknown. The experimental design also contained constraints that limit mechanistic interpretation. The absence of key experimental controls, specifically self-grafted (homograft) controls (tomato-on-tomato, potato-on-potato) and reciprocal grafts (potato scions onto tomato rootstocks), makes it impossible to distinguish effects specifically attributable to heterografting from general responses to the grafting process itself or to understand directionality in scion-rootstock interactions. Additionally, this study quantified phenotypic outcomes but did not measure underlying physiological processes. Interpretations regarding hormonal signaling such as gibberellin-mediated height suppression, enhanced resource acquisition, or source-sink dynamics remain speculative without supporting data on nutrient and water uptake efficiency, hormone profiles across the graft union, photosynthetic rates and assimilate partitioning, root system architecture, and tuberization signaling pathways. The study also did not evaluate whether potato rootstock confers disease resistance to the tomato scion or whether the composite plant shows altered susceptibility to pathogens affecting either component. Finally, although graft success rates were not systematically reported, variable replication numbers (ranging from 5 to 10 across measurements) suggest possible differential survival or sample loss that could influence results, and this omission limits assessment of the technique's practical reliability. To address these limitations and advance this promising technique toward practical application, several research priorities are identified. Field validation trials across diverse agro-ecological zones in Sri Lanka are essential to assess environmental robustness, economic viability, and performance under real-world pest and disease pressure, and these should include both protected cultivation and open-field comparisons. Systematic evaluation of a broader portfolio of tomato scion varieties and potato rootstocks is needed to identify compatibility rules and discover optimally synergistic combinations. Investigations into physiological mechanisms using isotope tracing for assimilate partitioning, hormone quantification across the graft union, and root system characterization are necessary to understand the mechanistic basis of synergistic versus competitive interactions. Explicit challenge trials with major soil-borne pathogens would quantify whether potato rootstocks confer resistance benefits to tomato scions, which represents a key potential advantage for smallholder adoption. Systematic investigation of factors affecting graft success would improve technique reliability for extension dissemination, while cost-benefit analysis comparing heterografting to conventional separate cultivation is essential to determine economic viability for smallholder farmers. Finally, studies extending beyond single-season evaluations to assess perennial performance or ratoon cropping potential would determine whether heterografted plants offer multi-season productivity benefits. 4. Conclusions and Recommendations This study provides evidence that heterografting tomato scions onto potato rootstocks is a technically feasible approach for integrated crop production under controlled environmental conditions. The cleft grafting method successfully produced functional composite plants capable of yielding both tomato fruits and potato tubers simultaneously. The most significant finding is the scion-dependent nature of system productivity. The Granola/Padma combination demonstrated synergistic potential, with substantial increases in both tomato fruit yield (approximately 2.8-fold) and potato tuber yield (approximately 2.1-fold) compared to non-grafted controls under the conditions tested. This yield enhancement was primarily driven by increased number of reproductive sinks (fruits and tubers) rather than increased individual organ size, and these productivity gains were achieved without compromising fruit quality and with only minor delays in harvest timing of five to nine days. However, these promising results must be interpreted within the study's limitations. The contrasting performance of the Granola/ Thilina combination, which showed enhanced tomato yield but suppressed tuber production, demonstrates that positive outcomes are not universal but require specific scion-rootstock compatibility. Furthermore, as a single-season controlled-environment study with a limited genetic sample and without critical experimental controls including self-grafted plants and reciprocal grafts, these findings should be considered a proof-of-concept requiring validation under diverse field conditions before widespread recommendation. Therefore, tomato-potato heterografting represents a promising model for vertical intensification that merits further investigation. The technique offers a potential pathway to enhance land-use efficiency in space-constrained agricultural systems, but its translation from research concept to practical application depends on addressing the knowledge gaps identified above. For researchers, it is recommended that future work prioritize field validation trials across multiple agro-ecological zones to establish environmental robustness, conduct mechanistic studies to elucidate hormonal and assimilate partitioning dynamics underlying scion-rootstock interactions, expand genetic screening to identify optimally compatible combinations and establish predictive compatibility criteria, and include appropriate controls such as self-grafted plants in future experimental designs. For agricultural extension services, it is advisable to monitor field validation outcomes before developing training materials, establish demonstration plots only after multi-location field data confirm consistent performance, and develop clear guidelines for graft success optimization based on systematic protocol research. For growers and smallholders, heterografting should be approached as an experimental technique requiring careful evaluation under local conditions, beginning with small-scale trials using the Granola/Padma combination which showed promise in this study, while maintaining realistic expectations regarding variability and the need for skill development in grafting technique and documenting local experiences to contribute to the collective knowledge base. For policymakers and research funders, support should be directed toward the priority research areas identified, particularly field validation and physiological mechanism studies, with recognition of heterografting as a long-term research and development investment rather than an immediately deployable technology, while facilitating collaboration between research institutions and extension services to ensure science-based technology transfer. In summary, this study establishes a foundation for understanding tomato-potato heterografting as a potential intensification strategy, and realizing this potential will require sustained, systematic research to transform these preliminary findings into reliable, science-based recommendations for agricultural practice. Declarations Competing interests : The authors declare no competing interests. Funding: The authors did not receive support from any organization for the submitted work. Author Contributions: Conceptualization: K.M.R.D. Abhayapala; Methodology: K.M.R.D. Abhayapala and P.D. Abeythilakarathe; Formal analysis and investigation: K.M.R.D. Abhayapala, A.A.L.C. Perera, and P.N.M.S. Piyarathne; Writing - original draft preparation: K.M.R.D. Abhayapala, A.A.L.C. Perera, and P.N.M.S. Piyarathne; Writing - review and editing: K.M.R.D. Abhayapala; Supervision: K.M.R.D. Abhayapala and P.D. Abeythilakarathe Data Availability: All data are presented in the manuscript in summarized form. Raw data are available upon request. References Asseng S, Cammarano D, Basso B, Chung U, Alderman PD, Sonder K, Reynolds M, Lobell DB (2017) Hot spots of wheat yield decline with rising temperatures. Glob Change Biol 23:2464–2472. https://doi.org/10.1111/gcb.13530 Chandrasena DPN, Wathugala DL, Prematilake VA (2020) Evaluation of potato ( Solanum tuberosum L.) genotypes for resistance to bacterial wilt ( Ralstonia solanacearum ) in the upcountry of Sri Lanka. Potato Res 63:439–453. https://doi.org/10.1007/s11540-020-09450-4 FAO (2017) The future of food and agriculture – Trends and challenges. Food and Agriculture Organization of the United Nations, Rome Fernie AR, Bachem CWB (2021) Metabolomics of potato–plant development and its response to stress. Potato Res 64:301–304. https://doi.org/10.1007/s11540-021-09515-w Gamelin FX, Baquet G, Berthoin S, Thevenet D, Nourry C, Nottin S, Bosquet L (2009) Effect of high intensity intermittent training on heart rate variability in prepubescent children. Eur J Appl Physiol 105:731–738. https://doi.org/10.1007/s00421-008-0955-8 Gisbert C, Prohens J, Raigón MD, Stommel JR, Nuez F (2011) Eggplant relatives as sources of variation for developing new rootstocks: effects of grafting on eggplant yield and fruit apparent quality and composition. Sci Hortic 128:14–22. https://doi.org/10.1016/j.scienta.2010.12.007 Goldschmidt EE (2014) Plant grafting: new mechanisms, evolutionary implications. Front Plant Sci 5:727. https://doi.org/10.3389/fpls.2014.00727 Kumar P, Lucini L, Rouphael Y, Cardarelli M, Kalunke RM, Colla G (2015) Insight into the role of grafting and arbuscular mycorrhiza on cadmium stress tolerance in tomato. Front Plant Sci 6:477. https://doi.org/10.3389/fpls.2015.00477 Kumar P, Lucini L, Rouphael Y, Cardarelli M, Kalunke RM, Colla G (2015) Insight into the role of grafting and arbuscular mycorrhiza on cadmium stress tolerance in tomato. Front Plant Sci 6:477. https://doi.org/10.3389/fpls.2015.00477 Kumar P, Pandey SK, Singh BP, Singh S, Singh D (2017) Heterografting in potato and tomato: A sustainable technology for enhancing productivity. Indian J Agric Sci 87:303–311 Kyriacou MC, Rouphael Y, Di Gioia F, Kyratzis A, Serio F, Renna M, De Pascale S, Santamaria P (2017) Micro-scale vegetable production and the rise of microgreens. Trends Food Sci Technol 57:103–115. https://doi.org/10.1016/j.tifs.2016.09.005 Obrero Á, Lopera CS, García MC (2020) The potential of interspecific grafting in horticulture: a review. Agronomy 10(11):1738. https://doi.org/10.3390/agronomy10111738 Pandey SK, Singh D, Singh BP (2017) Challenges and strategies for enhancing potato production in tropical and subtropical regions. In: Chakrabarti SK, Xie C, Tiwari JK (eds) The Potato Genome. Springer, Cham, pp 257–272. https://doi.org/10.1007/978-3-319-66135-3_16 Prematilake VA, Gajanayake J, Bandaranayake PC (2018) Impact of root-knot nematode ( Meloidogyne incognita ) on the growth and yield of tomato ( Solanum lycopersicum L.) in Sri Lanka. J Nat Sci Found Sri 46(4):429–438. https://doi.org/10.4038/jnsfsr.v46i4.8635 Savvas D, Colla G, Rouphael Y, Schwarz D (2010) Amelioration of heavy metal and nutrient stress in fruit vegetables by grafting. Sci Hortic 127:156–161. https://doi.org/10.1016/j.scienta.2010.09.011 Singh H, Kumar P, Chaudhari S, Edelstein M (2017) Tomato grafting: A global perspective. HortScience 52(10):1328–1336. https://doi.org/10.21273/HORTSCI11996-17 Slifka MK, Whitton JL (2000) Clinical implications of dysregulated cytokine production. J Mol Med. https://doi.org/10.1007/s001090000086 Wishart J, George TS, Brown LK, Ramsay G, Bradshaw JE, White PJ, Gregory PJ (2013) Measuring variation in potato roots in both field and glasshouse: the search for useful yield predictors and a simple screen for root traits. Potato Res 56:245–261. https://doi.org/10.1007/s11540-013-9240-2 Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 19 Apr, 2026 Reviewers invited by journal 14 Apr, 2026 Editor invited by journal 25 Mar, 2026 Editor assigned by journal 25 Mar, 2026 First submitted to journal 24 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9199706","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":622901575,"identity":"a2d1d0e4-bf27-4177-9e6e-e0d3f6699c91","order_by":0,"name":"A.A.L.C. Perera","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIiWNgGAWjYBACPgYehgMMDBYM/OzNQJpBQoagFjaIFgkGyZ5jCSAtPERpAalkMLiRYwBiEaGF/ezBw5VtEvIMN3I+v7pRY8HDwH746Aa8WnjyEg6ebZMwbOx5u8065xjQYTxpaTfwOyzH4GBjm0QCM3vuNuMcNqAWCR4z/Fr430C0APU+M875R4wWCagtPBw5zI9z24jSArSl4ZyE4QyeY2bMuX0SPGyE/MLPn2P8saHMRt7+ePPjzznf6uT42Q8fw6sF1UYwSaxyEGD+QIrqUTAKRsEoGDkAALheQ3DfWUQUAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-9003-7947","institution":"Rajarata University of Sri Lanka Faculty of Agriculture","correspondingAuthor":true,"prefix":"","firstName":"A.A.L.C.","middleName":"","lastName":"Perera","suffix":""},{"id":622901576,"identity":"6062b832-db98-4383-a480-4f0541e45c5a","order_by":1,"name":"K.M.R.D. Abhayapala","email":"","orcid":"","institution":"University of Sri Jayewardenepura","correspondingAuthor":false,"prefix":"","firstName":"K.M.R.D.","middleName":"","lastName":"Abhayapala","suffix":""},{"id":622901577,"identity":"13c41804-575f-4192-8ec4-4bdc336e4388","order_by":2,"name":"P.N.M.S. Piyarathne","email":"","orcid":"","institution":"Rajarata University of Sri Lanka Faculty of Agriculture","correspondingAuthor":false,"prefix":"","firstName":"P.N.M.S.","middleName":"","lastName":"Piyarathne","suffix":""},{"id":622901578,"identity":"433d597c-62a7-4ee2-9bfb-70430911be26","order_by":3,"name":"S.M.C.M Samarakoon","email":"","orcid":"","institution":"University of Sri Jayewardenepura","correspondingAuthor":false,"prefix":"","firstName":"S.M.C.M","middleName":"","lastName":"Samarakoon","suffix":""},{"id":622901579,"identity":"4a6ecdfc-90ac-4b2f-8077-a70327bb2fb3","order_by":4,"name":"P.D. Abeythilakarathe","email":"","orcid":"","institution":"Agriculture Research Station - Seetha Eliya","correspondingAuthor":false,"prefix":"","firstName":"P.D.","middleName":"","lastName":"Abeythilakarathe","suffix":""}],"badges":[],"createdAt":"2026-03-23 11:13:01","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9199706/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9199706/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107460358,"identity":"ca2f7367-5a0f-4229-92cc-b6514032a62b","added_by":"auto","created_at":"2026-04-21 16:44:01","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":85775,"visible":true,"origin":"","legend":"\u003cp\u003eTemporal dynamics of vegetative growth in grafted and non-grafted tomato plants from 4 to 22 weeks after planting. (a) Plant height (cm) progression over time. (b) Total leaf number accumulation over time. Data points represent mean values ± standard error (SE). Grafted plants (Granola/Padma and Granola/Thilina) exhibited reduced height compared to non-grafted controls while maintaining or increasing leaf number. Arrow indicates time of grafting (30 days after planting). n = 7-10 plants per treatment.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9199706/v1/e0b3deac98192ac4b3c54e9a.png"},{"id":107460359,"identity":"b7bb2349-9c70-47fc-b740-9b2e78501557","added_by":"auto","created_at":"2026-04-21 16:44:01","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":67552,"visible":true,"origin":"","legend":"\u003cp\u003eYield components of grafted and non-grafted tomato scions. (a) Mean total fruit yield per plant (g). (b) Mean number of fruits per plant. (c) Mean individual fruit weight (g). Bars represent mean ± standard error (SE). Different letters above bars indicate statistically significant differences according to Fisher's LSD test (p ≤ 0.05). Grafted Granola/\u003cem\u003ePadma\u003c/em\u003eand Granola/\u003cem\u003eThilina\u003c/em\u003e combinations both showed significant yield increases compared to non-grafted controls, driven primarily by increased fruit number rather than individual fruit size. n = 5-6 plants per treatment.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9199706/v1/4e1db63e068d4c7f0e222499.png"},{"id":107460362,"identity":"59d37844-5236-4244-bb36-8fcc9c77bb41","added_by":"auto","created_at":"2026-04-21 16:44:01","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":61648,"visible":true,"origin":"","legend":"\u003cp\u003eYield components of non-grafted and heterografted potato (Granola) rootstocks. (a) Mean total tuber yield per plant (g). (b) Mean number of tubers per plant. (c) Mean individual tuber weight (g). Bars represent mean ± standard error (SE). Different letters above bars indicate statistically significant differences according to Fisher's LSD test (p ≤ 0.05). The Granola/Padma combination produced significantly higher tuber yield than non-grafted controls, while the Granola/Thilina combination showed reduced tuber number and yield. Individual tuber weight was not significantly affected by grafting. n = 5 plants per treatment for yield and weight measurements; n = 6 for tuber number.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9199706/v1/143cd98037664f733b5670a2.png"},{"id":107460360,"identity":"854c43a7-d89f-404b-b85b-daa907d87f0b","added_by":"auto","created_at":"2026-04-21 16:44:01","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":170658,"visible":true,"origin":"","legend":"\u003cp\u003ePhenological development of grafted and non-grafted tomato plants. Bars show days after planting (DAP) to reach 50% flowering (blue bars) and 50% fruit set (orange bars) for each treatment. Grafted plants exhibited minor delays in reproductive development compared to non-grafted controls, with the Granola/Padma combination showing the longest delay (5 days to flowering, 8 days to fruit set). Values derived from observations of all plants per treatment (n = 10).\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9199706/v1/4e69b2e194500b1b41f36a32.jpeg"},{"id":107490363,"identity":"e3d73200-1691-43a7-aecc-3bedcaeaf6fc","added_by":"auto","created_at":"2026-04-22 02:51:57","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":29997,"visible":true,"origin":"","legend":"\u003cp\u003eFruit dimensional analysis of grafted and non-grafted tomato plants. Scatter plot shows individual fruit measurements of diameter (cm) versus length (cm), clustered by treatment. Each point represents an individual fruit. The \u003cem\u003ePadma\u003c/em\u003evarieties (both grafted and non-grafted) maintained their characteristic elongated fruit shape (higher length:diameter ratio), while Thilina varieties maintained round fruit morphology. Grafting did not significantly alter fruit dimensions within each variety, although grafted Granola/Padma fruits showed a non-significant trend toward increased length. Data based on 10-15 fruits per treatment.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-9199706/v1/2128d5d78eb0a40acb2323fe.png"},{"id":107705698,"identity":"b77bd679-a30e-44fd-b131-67a7a692734b","added_by":"auto","created_at":"2026-04-24 09:14:37","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":676405,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9199706/v1/35fc428d-4401-49e8-b749-6ee4d11c7397.pdf"}],"financialInterests":"","formattedTitle":"Evaluating Tomato-Potato Heterografting for Enhanced Crop Performance in Sri Lanka","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eGlobal agricultural systems face the dual imperative of intensifying food production to meet the demands of a growing population while adapting to the constraints of limited arable land and climate variability (FAO \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). This challenge is particularly acute for vegetable cultivation, a vital source of nutrition and income for smallholder farmers. In regions like Sri Lanka, production of high-value solanaceous crops such as tomato (\u003cem\u003eSolanum lycopersicum\u003c/em\u003e L.) and potato (\u003cem\u003eSolanum tuberosum\u003c/em\u003e L.) is often hampered by persistent challenges. Potato cultivation, for instance, is severely impacted by soil-borne diseases like bacterial wilt (\u003cem\u003eRalstonia solanacearum\u003c/em\u003e) and late blight (\u003cem\u003ePhytophthora infestans\u003c/em\u003e), which can cause devastating yield losses (Pandey et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Chandrasena et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Similarly, tomato production is frequently constrained by the same soil-borne pathogens, as well as root-knot nematodes (\u003cem\u003eMeloidogyne\u003c/em\u003e spp.), leading to significant annual deficits (Prematilake et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eVegetable grafting has emerged as a pivotal horticultural technology to mitigate these production constraints. By surgically joining a desirable scion cultivar to a vigorous, stress-resistant rootstock, grafting can enhance plant vigor, increase yield, and improve tolerance to environmental stresses and soil pathogens (Savvas et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Kyriacou et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The use of resistant rootstocks is considered a key component of integrated pest management and a sustainable alternative to soil fumigation (Singh et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). While homografting (within the same species) is common, heterografting between different species within the same family offers a unique opportunity to combine complementary traits. For instance, grafting tomato onto disease-resistant eggplant rootstocks is a proven strategy to manage bacterial wilt (Gisbert et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). However, the practical application of grafting in many developing agricultural contexts remains limited by access to specialized rootstock seed and technical knowledge.\u003c/p\u003e \u003cp\u003eTomato and potato, both members of the Solanaceae family, are prime candidates for heterografting. They share sufficient genetic proximity for graft compatibility while offering distinct and potentially synergistic advantages. The potato plant is known for its robust and extensive root system, which is highly efficient at water and nutrient uptake (Wishart et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Utilizing potato as a rootstock could theoretically provide a stronger foundation for a tomato scion, potentially enhancing its resilience and productivity. Conceptually, a successful heterografted plant could yield both tomato fruits from the scion and potato tubers from the rootstock, thereby maximizing land productivity, a concept of significant value for space-limited cultivation systems and home gardens (Obrero et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This \"double-cropping\" approach from a single plant has the potential to improve land use efficiency substantially.\u003c/p\u003e \u003cp\u003eDespite this compelling potential, research on tomato-potato heterografting remains sparse and inconsistent. Existing studies are often anecdotal or lack rigorous agronomic and physiological evaluation under controlled conditions. Key questions regarding the optimal grafting technique, the impact on the phenology and yield dynamics of both components, and the underlying physiological mechanisms of resource partitioning remain largely unanswered. For example, the influence of a fruiting tomato scion on the tuberization signals and sink strength of a potato rootstock is not well understood (Fernie and Bachem \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This knowledge gap hinders the development of this technique as a reliable, science-based practice for growers.\u003c/p\u003e \u003cp\u003eTherefore, this study was designed to systematically evaluate the viability and agronomic performance of heterografting commercially important tomato varieties (\u003cem\u003eThilina\u003c/em\u003e and \u003cem\u003ePadma\u003c/em\u003e) onto a potato (Granola) rootstock under the protected cultivation system of Sri Lanka's up-country region. The specific objectives were to: (1) assess the success rate of cleft grafting between tomato scions and potato rootstocks; (2) evaluate the effects of heterografting on the growth, yield, and phenology of the tomato scion; and (3) determine the impact of the tomato scion on the tuber yield and quality of the potato rootstock\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1. Experimental Site and Growing Conditions\u003c/h2\u003e\n \u003cp\u003eThe study was conducted from May to December 2024 in a polyethylene-covered polytunnel at the Agriculture Research and Development Centre, Sita-Eliya, Nuwara-Eliya, Sri Lanka (6\u0026deg;58\u0026apos;N, 80\u0026deg;46\u0026apos;E, altitude 1860 m above mean sea level). This location is within a major potato and temperate vegetable growing region characterized by a humid subtropical highland climate. The polytunnel environment was maintained to mitigate excessive rainfall and temperature fluctuations, with average daily temperatures ranging from 15\u0026deg;C to 22\u0026deg;C and natural photoperiod throughout the trial.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2. Plant Materials and Cultivation\u003c/h2\u003e\n \u003cp\u003eTwo tomato (\u003cem\u003eS. lycopersicum\u003c/em\u003e L.) varieties, \u003cem\u003eThilina\u003c/em\u003e (indeterminate vine habit) and \u003cem\u003ePadma\u003c/em\u003e (determinate bush habit), were used as scions. The potato (\u003cem\u003eS. tuberosum\u003c/em\u003e L.) cultivar Granola was selected as the rootstock for its regional adaptability and vigorous growth. A sterile, well-draining substrate was prepared by mixing burnt paddy husk and composted tea waste (1:1 v/v), which was subsequently steam-sterilized at 100\u0026deg;C for 8 hours. Tomato seeds were sown directly into 15 cm diameter pots filled with this substrate. Certified disease-free Granola seed tubers were planted individually in separate pots to develop rootstock plants. All plants were irrigated using a drip system and fertilized weekly with a standard Albert solution (2 g L⁻\u0026sup1;) as per the recommendation of the Department of Agriculture, Sri Lanka.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3. Grafting Technique and Healing Management\u003c/h2\u003e\n \u003cp\u003eCleft grafting was performed 30 days after planting (DAP), when both scion and rootstock stems attained a uniform diameter of 4.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 mm. The rootstock was decapitated horizontally, and a vertical incision (1.5\u0026ndash;2.0 cm deep) was made in the center of the stump. A matching scion, excised from the tomato seedling to include 2\u0026ndash;3 fully expanded leaves, was shaped into a wedge. The scion was inserted into the rootstock cleft, ensuring firm cambial contact on at least one side. The graft union was secured immediately with a biodegradable grafting clip. To promote healing, each grafted plant was covered with a transparent polyethylene bag to maintain high relative humidity (\u0026gt;\u0026thinsp;90%) for 14 days. The bags were removed after confirming successful union, indicated by scion turgidity and new leaf growth.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e2.4. Experimental Design and Treatments\u003c/h2\u003e\n \u003cp\u003eThe experiment was arranged in a Complete Randomized Design (CRD) with ten replications per treatment. The five treatments were:\u003c/p\u003e\n \u003col\u003e\n \u003cli\u003e\u003cspan\u003eNon-grafted potato Granola (rootstock control)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e \u003cspan\u003eNon-grafted tomato \u003cem\u003eThilina\u003c/em\u003e (scion control)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u0026nbsp;\u003cspan\u003eNon-grafted tomato \u003cem\u003ePadma\u003c/em\u003e (scion control)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e \u003cspan\u003eHeterograft of Granola (rootstock) and \u003cem\u003eThilina\u003c/em\u003e (scion)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e \u003cspan\u003eHeterograft of Granola (rootstock) and\u0026nbsp;\u003cem\u003ePadma\u003c/em\u003e (scion)\u003cbr\u003e\u003c/span\u003e\u003c/li\u003e\n \u003c/ol\u003e\n \u003cp\u003eAll plants were individually potted and spaced at 50 \u0026times; 50 cm. Standard integrated pest management practices were followed. A fungicide (cymoxanil 8% + mancozeb 64%) was applied three times as a preventive spray against late blight (\u003cem\u003ePhytophthora infestans\u003c/em\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e2.5. Data Collection\u003c/h2\u003e\n \u003cp\u003eData were collected on growth, phenology, and yield components.\u003c/p\u003e\n \u003cp\u003eGrowth Parameters: Plant height (from soil surface to the apical meristem) and total leaf number were recorded from eight randomly selected plants per treatment at 14-day intervals, commencing 14 days after grafting.\u003c/p\u003e\n \u003cp\u003ePhenological Parameters: The number of days from planting to 50% flowering, 50% fruit set, and first harvestable fruit (at 50% surface ripening) was recorded for tomato.\u003c/p\u003e\n \u003cp\u003eYield and Yield Components (at physiological maturity):\u003c/p\u003e\n \u003cul\u003e\n \u003cli\u003e\n \u003cp\u003eTomato: Total number of fruits per plant, mean individual fruit weight (g), and total fruit yield per plant (g).\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003ePotato: Total number of tubers per plant (diameter\u0026thinsp;\u0026ge;\u0026thinsp;2.5 cm), mean individual tuber weight (g), and total tuber yield per plant (g). Harvest occurred at 120 DAP, corresponding to full vine senescence.\u003c/p\u003e\n \u003c/li\u003e\n \u003c/ul\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e2.6. Statistical Analysis\u003c/h2\u003e\n \u003cp\u003eAll collected data were subjected to Analysis of Variance (ANOVA) using Minitab Statistical Software (Version 18.0). The significance of treatment means was tested using Fisher\u0026rsquo;s Least Significant Difference (LSD) test at a 5% probability level (p\u0026thinsp;\u0026le;\u0026thinsp;0.05). Relationships between key yield components (e.g., fruit number vs. yield) were examined using Pearson\u0026rsquo;s correlation analysis. Data are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard error (SE).\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. Growth Performance of Grafted and Non-Grafted Tomato Plants\u003c/h2\u003e\n \u003cp\u003eThe heterografting of tomato scions onto potato rootstock induced significant and consistent modifications to the vegetative growth architecture of the tomato component. Analysis of the longitudinal dataset for plant height and total leaf number revealed a clear physiological pattern: grafted plants developed a more compact architecture while maintaining, or even enhancing, their foliar capacity compared to non-grafted controls. This dissociation between vertical extension and leaf production highlights a distinct rootstock-mediated regulation of growth.\u003c/p\u003e\n \u003cp\u003eA significant main effect of treatment was observed for final plant height (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Grafted plants exhibited a pronounced reduction in vertical growth. Non-grafted Tomato (\u003cem\u003ePadma\u003c/em\u003e) and Non-grafted Tomato (\u003cem\u003eThilina\u003c/em\u003e) controls reached average final heights of 113.03 cm and 103.16 cm, respectively. In contrast, their grafted counterparts, Granola\u003cem\u003e/Padma\u003c/em\u003e and Granola/\u003cem\u003eThilina\u003c/em\u003e, attained significantly lower average heights of 86.47 cm and 81.43 cm (Table \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This represents a substantial reduction of approximately 23.5% for grafted Granola\u003cem\u003e/Padma\u003c/em\u003e and 21.1% for grafted Granola/\u003cem\u003eThilina\u003c/em\u003e plants. The plant height curves in Fig. 1a illustrate that this suppression was not merely a final outcome but a consistent trend, with the growth trajectories of grafted plants diverging from controls early in development and maintaining a lower slope throughout.\u003c/p\u003e\n \u003cp\u003eIn stark contrast to height, the final total leaf number was not adversely affected by grafting. No significant differences (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05) were found between grafted and non-grafted \u003cem\u003ePadma\u003c/em\u003e plants, with averages of 124.8 and 124.0 leaves, respectively (Table \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Notably, grafted Granola/\u003cem\u003eThilina\u003c/em\u003e plants supported a significantly greater final leaf number (236.0) compared to non-grafted T plants (173.2). The curves showing number of leaves in Fig. 1b show that while the \u003cem\u003ePadma\u003c/em\u003e varieties maintained parallel trajectories, the grafted Granola/\u003cem\u003eThilina\u003c/em\u003e combination consistently produced more leaves than its non-grafted control from the early stages, indicating a sustained enhancement in leaf initiation or retention.\u0026nbsp;\u003c/p\u003e\n \u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eFinal growth parameters of grafted and non-grafted tomato plants at the last measurement interval\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eDescription\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003eAvg. final height (cm)\u0026thinsp;\u0026plusmn;\u0026thinsp;SE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003eAvg. final leaf no. \u0026plusmn; SE\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eNon-grafted Tomato (\u003cem\u003ePadma\u003c/em\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e113.03\u0026thinsp;\u0026plusmn;\u0026thinsp;4.24 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e124.0\u0026thinsp;\u0026plusmn;\u0026thinsp;12.7 b\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eNon-grafted Tomato (\u003cem\u003eThilina\u003c/em\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e103.16\u0026thinsp;\u0026plusmn;\u0026thinsp;3.89 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e173.2\u0026thinsp;\u0026plusmn;\u0026thinsp;15.9 c\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola/\u003cem\u003ePadma\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e86.47\u0026thinsp;\u0026plusmn;\u0026thinsp;3.21 b\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e124.8\u0026thinsp;\u0026plusmn;\u0026thinsp;13.1 b\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola/\u003cem\u003eThilina\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e81.43\u0026thinsp;\u0026plusmn;\u0026thinsp;3.05 b\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e236.0\u0026thinsp;\u0026plusmn;\u0026thinsp;18.3 a\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eMeans within a column followed by different letters are significantly different according to Fisher\u0026apos;s LSD test (p \u0026le; 0.05). SE = Standard Error. Data are from the final recorded measurement for each surviving plant (n=7\u0026ndash;10).\u003c/p\u003e\n \u003cp\u003eThe observed growth modulation, significant height reduction without a compromise in leaf number is a classic manifestation of rootstock-scion interaction, aligning with established grafting physiology (Goldschmidt \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The compact stature of grafted plants likely results from altered hormonal signaling, particularly in gibberellin pathways, which are known to be transmitted across the graft union and regulate internode elongation. This dwarfing effect is not indicative of poor vigor but rather a reallocation of resources. The maintenance or increase in leaf number, as clearly seen in the grafted Granola/\u003cem\u003eThilina\u003c/em\u003e combination, confirms that the photosynthetic source capacity is preserved or enhanced.\u003c/p\u003e\n \u003cp\u003eThis architectural change has critical agronomic implications. A plant with reduced height but undiminished leaf area represents a more efficient, compact growth habit. It can improve light distribution within the canopy, reduce mutual shading, lower the risk of lodging, and facilitate management practices in protected cultivation systems like polytunnels (Singh et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Importantly, this structure suggests an optimization where resources may be diverted from supporting excessive vegetative framework (stems) towards productive sinks namely, fruits and tubers. The robust potato rootstock (Granola), known for a vigorous root system (Wishart et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), appears to support a prolific leaf canopy while simultaneously exerting a regulatory effect on scion height, creating an ideal morphology for a dual-cropping system aimed at maximizing yield per unit area. This finding supports the potential of heterografting as a tool not just for stress resistance, but for tailored growth management (Kumar et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Obrero et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. Yield and Yield Components of Tomato Scions\u003c/h2\u003e\n \u003cp\u003eHeterografting onto potato rootstock profoundly and significantly enhanced the reproductive performance of tomato scions. The yield advantage was not only substantial in magnitude but also consistent across both scion cultivars, fundamentally altering the productivity profile compared to non-grafted controls. The data reveal that this increase was mechanistically driven by a dramatic improvement in fruit set rather than by enlarging individual fruit size. A summary of the key yield parameters for all tomato-based treatments is presented in Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The overall impact on total fruit yield, number of fruits, and individual fruit weight are visualized in Fig.\u0026nbsp;2.\u003c/p\u003e\n \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.1 Total Fruit Yield and Fruit Number\u003c/h2\u003e\n \u003cp\u003eHeterografting resulted in a transformative increase in total yield (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The Granola\u003cem\u003e/Padma\u003c/em\u003e combination was exceptionally productive, with an average yield of 891.49 g per plant. This represents a 2.8-fold increase over the non-grafted \u003cem\u003ePadma\u003c/em\u003e control, which yielded 317.71 g per plant. Similarly, the Granola\u003cem\u003e/Thilina\u003c/em\u003e graft yielded an average of 546.37 g per plant, a 3.8-fold increase over the non-grafted \u003cem\u003eThilina\u003c/em\u003e yield of 142.45 g (Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThis remarkable yield enhancement was unequivocally driven by a significant increase in the number of fruits harvested per plant. Grafted plants consistently set and matured more fruits (Fig.\u0026nbsp;2b). The average fruit number for grafted Granola\u003cem\u003e/Padma\u003c/em\u003e plants (20.2) was 2.2 times greater than for P plants (9.0). Grafted Granola/\u003cem\u003eThilina\u003c/em\u003e plants also produced more than double the fruits (14.8) of non-grafted \u003cem\u003eThilina\u003c/em\u003e plants (5.7) (Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Correlation analysis confirmed a very strong positive relationship between total fruit yield and fruit number per plant across all individuals (r\u0026thinsp;=\u0026thinsp;0.97, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.2 Individual Fruit Weight\u003c/h2\u003e\n \u003cp\u003eIn contrast to fruit number, the mean weight of individual fruits was not significantly increased by grafting (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). The average fruit weight for grafted plants (grafted Granola\u003cem\u003e/Padma\u003c/em\u003e: 43.94 g; grafted Granola/\u003cem\u003eThilina\u003c/em\u003e: 40.08 g) was statistically comparable to that of their non-grafted counterparts (P: 39.71 g; T: 36.18 g) (Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). \u0026nbsp;\u003c/p\u003e\n \u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eYield and yield components of grafted and non-grafted tomato scions\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eTreatment\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003eAvg. fruit no. per plant\u0026thinsp;\u0026plusmn;\u0026thinsp;SE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003eAvg. individual fruit weight (g)\u0026thinsp;\u0026plusmn;\u0026thinsp;SE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003eAvg. total fruit yield per plant (g)\u0026thinsp;\u0026plusmn;\u0026thinsp;SE\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eNon-grafted Tomato (\u003cem\u003eThilina\u003c/em\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e5.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8 c\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e36.18\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e142.45\u0026thinsp;\u0026plusmn;\u0026thinsp;77.1 c\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eNon-grafted Tomato (\u003cem\u003ePadma\u003c/em\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e9.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 b\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e39.71\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e317.71\u0026thinsp;\u0026plusmn;\u0026thinsp;47.2 b\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola/\u003cem\u003eThilina\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e14.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e40.08\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e546.37\u0026thinsp;\u0026plusmn;\u0026thinsp;58.9 a\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola/\u003cem\u003ePadma\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e20.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e43.94\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e891.49\u0026thinsp;\u0026plusmn;\u0026thinsp;72.4 a\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eMeans within a column followed by different letters are significantly different according to Fisher\u0026apos;s LSD test (p \u0026le; 0.05). SE = Standard Error. Data based on n=5\u0026ndash;6 plants per treatment.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.3 Phenology of Harvest\u003c/h2\u003e\n \u003cp\u003eThe timing of first harvestable fruit was slightly delayed in grafted plants. Non-grafted tomatoes reached first harvest 153 DAP. Grafted Granola/\u003cem\u003eThilina\u003c/em\u003e and Granola\u003cem\u003e/Padma\u003c/em\u003e plants were harvested at 158 DAP and 162 DAP, respectively, indicating a delay of 5\u0026ndash;9 days (Table \u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This modest delay is likely attributable to the initial resource allocation required for graft union healing and acclimation. \u0026nbsp;\u003c/p\u003e\n \u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDays from planting to first harvestable fruit\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eTreatment\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003ePlanted date\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003eGrafted date\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003eFirst harvest date\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c5\"\u003e\n \u003cp\u003eDays after planting (DAP)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eNon-grafted Tomato (\u003cem\u003eThilina\u003c/em\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\n \u003cp\u003e2025.05.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003eNot Applicable\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\n \u003cp\u003e2025.10.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\n \u003cp\u003e153\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eNon-grafted Tomato (\u003cem\u003ePadma\u003c/em\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\n \u003cp\u003e2025.05.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003eNot Applicable\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\n \u003cp\u003e2025.10.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\n \u003cp\u003e153\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola/\u003cem\u003eThilina\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\n \u003cp\u003e2025.05.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e2025.06.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\n \u003cp\u003e2025.10.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\n \u003cp\u003e158\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola/\u003cem\u003ePadma\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\n \u003cp\u003e2025.05.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e2025.06.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\n \u003cp\u003e2025.11.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\n \u003cp\u003e162\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eThe results demonstrate that tomato-potato heterografting is a highly effective strategy for yield intensification, primarily through the physiological mechanism of enhanced fruit set. The robust, perennial-like root system of the potato rootstock Granola likely provides superior and more stable access to water and nutrients during critical flowering and fruit-set stages. This mitigates abiotic stress that commonly leads to flower abortion in non-grafted plants, thereby allowing a greater proportion of flowers to develop into mature fruits (Kumar et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Savvas et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe finding that individual fruit weight remained unchanged is significant. It indicates that the yield gains were achieved without diluting resources across an excessive number of sinks, which can lead to smaller, unmarketable fruit. Instead, the potato rootstock effectively supported the increased sink demand created by the higher fruit number. This aligns with the concept of rootstock-mediated improvement in overall plant vigor and assimilate supply capacity (Goldschmidt \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The slight delay in phenology is a negligible trade-off considering the magnitude of yield increase and is common in grafted systems due to the initial recovery phase.\u003c/p\u003e\n \u003cp\u003eThe superior performance of the Granola\u003cem\u003e/Padma\u003c/em\u003e combination over Granola\u003cem\u003e/Thilina\u003c/em\u003e suggests a scion-specific interaction. The determinate growth habit of \u003cem\u003ePadma\u003c/em\u003e may synchronize better with the resource partitioning patterns induced by the potato rootstock, leading to more efficient conversion of vegetative resources into reproductive output. This underscores the importance of selecting optimal scion-rootstock combinations to maximize synergism in heterografting systems (Obrero et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Singh et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3. Yield and Yield Components of Potato Rootstocks\u003c/h2\u003e\n \u003cp\u003eThe heterografting system induced a significant and scion-dependent effect on the tuber yield of the potato (Granola) rootstock. This finding demonstrates that the presence and identity of a tomato scion directly influence the reproductive sink activity of the underground rootstock component. The potato\u0026apos;s response ranged from yield suppression to significant enhancement, highlighting a complex interplay of resource partitioning and source-sink signaling within the composite plant.\u003c/p\u003e\n \u003cp\u003eTotal Tuber Yield and Tuber Number: The total tuber yield per plant was significantly affected by the grafting treatment (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Notably, the effect was not uniform but depended entirely on the grafted tomato scion (Fig.\u0026nbsp;3a). The Granola/\u003cem\u003ePadma\u003c/em\u003e graft combination resulted in the highest average tuber yield of 324.31 g per plant, which was 1.9 times greater than the yield of the non-grafted Granola control (169.24 g) and significantly higher than all other treatments.\u003c/p\u003e\n \u003cp\u003eIn contrast, the Granola/\u003cem\u003eThilina\u003c/em\u003e combination produced an average yield of only 141.27 g per plant, which was not statistically different from the non-grafted control but represented a clear numerical reduction. This differential response was primarily driven by changes in the number of tubers set per plant (Table \u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The grafted Granola\u003cem\u003e/Padma\u003c/em\u003e plants produced an average of 8.0 tubers, a significant increase over the non-grafted G average of 7.8 tubers. The grafted Granola/\u003cem\u003eThilina\u003c/em\u003e plants, however, produced only 3.4 tubers on average, explaining their low total yield. Correlation analysis confirmed a strong positive relationship between total tuber yield and tuber number across all plants (r\u0026thinsp;=\u0026thinsp;0.88, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\n \u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eYield and yield components of non-grafted and heterografted potato rootstocks\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eTreatment\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003eAvg. tuber no. per plant\u0026thinsp;\u0026plusmn;\u0026thinsp;SE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003eAvg. individual tuber weight (g)\u0026thinsp;\u0026plusmn;\u0026thinsp;SE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003eAvg. total tuber yield per plant (g)\u0026thinsp;\u0026plusmn;\u0026thinsp;SE\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eNon-grafted Potato (Granola)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e7.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1 ab\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e37.86\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e169.24\u0026thinsp;\u0026plusmn;\u0026thinsp;21.4 b\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola/\u003cem\u003eThilina\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e3.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 c\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e42.73\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e141.27\u0026thinsp;\u0026plusmn;\u0026thinsp;24.1 b\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola/\u003cem\u003ePadma\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e8.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e41.09\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e324.31\u0026thinsp;\u0026plusmn;\u0026thinsp;47.5 a\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eMeans within a column followed by different letters are significantly different according to Fisher\u0026apos;s LSD test (p \u0026le; 0.05). SE = Standard Error. Data based on n=5 plants per treatment for yield/weight; tuber number includes n=6.\u003c/p\u003e\n \u003cp\u003eIndividual Tuber Weight: The mean weight of individual tubers was not significantly altered by heterografting (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). All treatments produced tubers of statistically equivalent size, with averages ranging from 37.86 g [Non-grafted tomato (\u003cem\u003eGranola\u003c/em\u003e)] to 42.73 g (grafted Granola/\u003cem\u003eThilina\u003c/em\u003e) (Table \u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, Fig. 3c). This indicates that the grafting treatments affected the initiation and set of tuber sinks rather than the process of tuber \u003cem\u003ebulking\u003c/em\u003e. The resources available to each established tuber remained consistent, regardless of the total number on the plant.\u003c/p\u003e\n \u003cp\u003eThe scion-specific yield outcomes for the potato rootstock represent a critical finding with important physiological implications. The enhanced tuber yield in the grafted Granola\u003cem\u003e/Padma\u003c/em\u003e combination suggests a synergistic, rather than competitive, relationship between the \u003cem\u003ePadma\u003c/em\u003e scion and the Granola rootstock. The highly productive \u003cem\u003ePadma\u003c/em\u003e canopy (as shown in Section \u003cspan refid=\"Sec11\" class=\"InternalRef\"\u003e3.2\u003c/span\u003e) likely acted as a powerful source of photo assimilates. A portion of these assimilates may have been translocated to the rootstock, stimulating stolon initiation and tuber set, thereby increasing sink number (Fernie \u0026amp; Bachem \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This aligns with the concept of graft unions facilitating bidirectional resource and signaling exchange (Goldschmidt \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eConversely, the lack of yield benefit and even a trend toward suppression, in the grafted Granola/\u003cem\u003eThilina\u003c/em\u003e combination indicates a competitive interaction. The \u003cem\u003eThilina\u003c/em\u003e scion, while more productive than its non-grafted form, may have been a stronger sink for resources or may have transmitted different hormonal signals that partially inhibited the tuberization process in the potato rootstock. The fact that individual tuber weight was maintained across all treatments suggests that once a tuber is initiated, it becomes a prioritized sink capable of drawing necessary resources, but grafting with \u003cem\u003eThilina\u003c/em\u003e severely limited the initiation event itself.\u003c/p\u003e\n \u003cp\u003eFrom an applied perspective, this underscores that successful double-cropping via heterografting requires the selection of compatible partners that establish a mutually beneficial or neutral resource-sharing relationship. The Granola/\u003cem\u003ePadma\u003c/em\u003e combination emerges as uniquely proficient, enhancing the yield of both components, tomato fruits and potato tubers, simultaneously. This synergistic effect leverages the robust root system of the potato (Wishart et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) and the high photosynthetic output of the \u003cem\u003ePadma\u003c/em\u003e scion to maximize overall land productivity, validating the core premise of this integrated cropping model (Kumar et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Obrero et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4. Phenology and Fruit Quality Parameters\u003c/h2\u003e\n \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.1. Phenological Development\u003c/h2\u003e\n \u003cp\u003eThe phenological development of the tomato scion was largely unaltered by heterografting onto potato rootstock. Analysis of key reproductive milestones revealed only minor, non-significant delays (Table \u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). For the \u003cem\u003eThilina\u003c/em\u003e varieties, the time to 50% flowering was identical at 100 DAP for both grafted (Granola/\u003cem\u003eThilina\u003c/em\u003e) and non-grafted \u003cem\u003eThilina\u003c/em\u003e plants. The subsequent 50% fruit set occurred at 111 DAP for non-grafted plants and 113 DAP for grafted plants, a negligible 2-day delay. A more pronounced but still modest delay was observed in the \u003cem\u003ePadma\u003c/em\u003e varieties, where grafting (Granola\u003cem\u003e/Padma\u003c/em\u003e) postponed 50% flowering by 5 days and 50% fruit set by 8 days compared to the non-grafted \u003cem\u003ePadma\u003c/em\u003e control. Consequently, the date of first harvestable fruit was delayed by 5 days for the grafted Granola/\u003cem\u003eThilina\u003c/em\u003e combination and 9 days for the grafted Granola\u003cem\u003e/Padma\u003c/em\u003e combination (Fig. \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e4\u003c/span\u003e). These delays are consistent with the typical resource allocation required for graft union healing and re-establishment of vascular flow, a common transient effect in vegetable grafting that does not disrupt crop cycle planning (Kumar et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Singh et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Critically, the grafting process did not induce juvenility or reset the developmental program, affirming the physiological compatibility of the heterograft system.\u0026nbsp;\u003c/p\u003e\n \u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePhenological development timeline of grafted and non-grafted tomato plants\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eTreatment\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003eDays to 50% flowering (DAP)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003eDays to 50% fruit set (DAP)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003eDays to first harvest (DAP)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eNon-grafted Tomato (\u003cem\u003eThilina)\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e111\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e153\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola\u003cem\u003e/Thilina\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e113 (+\u0026thinsp;2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e158 (+\u0026thinsp;5)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eNon-grafted Tomato (\u003cem\u003ePadma\u003c/em\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e153\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola\u003cem\u003e/Padma\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e83 (+\u0026thinsp;5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e104 (+\u0026thinsp;8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e162 (+\u0026thinsp;9)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eDAP = Days After Planting. Values in parentheses indicate delay relative to non\u0026minus;grafted control.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.2. Fruit Quality Attributes\u003c/h2\u003e\n \u003cp\u003eThe marketable quality of tomato fruits, assessed through physical dimensions, was preserved or even slightly enhanced by grafting (Table \u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). There was no significant effect of grafting on fruit diameter for either scion variety. However, a notable and positive trend was observed in fruit morphology. While the characteristic shape of each variety was maintained, \u003cem\u003eThilina\u003c/em\u003e fruits remained round and \u003cem\u003ePadma\u003c/em\u003e fruits elongated, the grafted Granola\u003cem\u003e/Padma\u003c/em\u003e fruits exhibited a non-significant increase in average length (5.28 cm) compared to their non-grafted counterparts (4.92 cm). This resulted in a preserved length-to-diameter ratio, confirming the maintenance of varietal typicity (Fig. \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The stability of fruit size alongside a dramatic increase in fruit number (Section \u003cspan refid=\"Sec11\" class=\"InternalRef\"\u003e3.2\u003c/span\u003e) indicates that the robust potato rootstock effectively supplied the necessary water and photo assimilates to support the enlarged sink demand without compromising individual fruit development. This aligns with findings that vigorous rootstocks can improve fruit quality by sustaining resource supply during critical growth phases (Gisbert et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Savvas et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e\n \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u0026nbsp;\u0026nbsp;\u003c/div\u003e\n \u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eFruit dimensional quality parameters of grafted and non-grafted tomato plants\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eTreatment\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003eAverage fruit diameter (cm)\u0026thinsp;\u0026plusmn;\u0026thinsp;SE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003eAverage fruit length (cm)\u0026thinsp;\u0026plusmn;\u0026thinsp;SE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003eLength-to-diameter ratio\u0026thinsp;\u0026plusmn;\u0026thinsp;SE\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eNon-grafted Tomato (\u003cem\u003eThilina)\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e4.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e4.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 b\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e0.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 b\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola\u003cem\u003e/Thilina\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e4.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e4.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05 b\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e0.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 b\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eNon-grafted Tomato (\u003cem\u003ePadma)\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e4.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e4.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e1.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04 a\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eGrafted\u0026nbsp;Granola\u003cem\u003e/Padma\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e4.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e5.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e1.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 a\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e*Means within a column followed by different letters are significantly different according to Fisher\u0026apos;s LSD test (p \u0026le; 0.05). SE = Standard Error.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5. Synthesis and Practical Implications\u003c/h2\u003e\n \u003cp\u003eThe collective findings of this study provide strong evidence for the agronomic viability and significant productive potential of tomato-potato heterografting as a novel double-cropping system. The results demonstrate that success is not universal but hinges on specific, compatible scion-rootstock combinations. The Granola/\u003cem\u003ePadma\u003c/em\u003e heterograft emerged as uniquely synergistic, delivering a transformative increase in total land productivity. This combination yielded 2.8 times more tomato fruit and 2.1 times more potato tubers per plant than non-grafted counterparts. This dual yield enhancement was primarily driven by a greater number of reproductive sinks, more fruits and tubers rather than an increase in their individual size. This suggests the robust potato rootstock improved the plant\u0026apos;s capacity to support reproductive development during critical setting phases, likely through enhanced resource acquisition, while the vigorous \u003cem\u003ePadma\u003c/em\u003e scion supplied ample photo assimilates that benefited both its own fruits and the rootstock\u0026apos;s tubers. Importantly, this substantial yield gain was achieved with only a minor delay in harvest phenology and no detriment to fruit quality, confirming the technique\u0026apos;s practical feasibility. From an applied perspective, this heterografting model offers a powerful strategy for vertical intensification, particularly for smallholders and home gardeners in Sri Lanka and similar regions where arable land is limited. It enables the concurrent production of two nutrient-rich crops from a single planting point, dramatically improving land-use efficiency and household food security without requiring advanced technology or compromising crop marketability.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\n \u003ch2\u003e3.6. Limitations and Future Research\u003c/h2\u003e\n \u003cp\u003eWhile this controlled-environment study provides compelling proof-of-concept for tomato-potato heterografting, several limitations must be acknowledged to contextualize the findings appropriately and guide future inquiry. The experiment was conducted under polytunnel conditions, which buffered against environmental stressors such as variable rainfall, wind, and extreme temperature fluctuations. Consequently, the performance and resilience of these heterografts under open-field conditions exposed to real-world abiotic stresses and full biotic pressure from soil-borne pathogens such as \u003cem\u003eRalstonia solanacearum\u003c/em\u003e remain to be evaluated. The controlled environment may have optimized conditions for graft establishment and resource partitioning, potentially overestimating the performance achievable under typical smallholder cultivation conditions. Furthermore, this study examined only two tomato scion varieties (\u003cem\u003eThilina\u003c/em\u003e and \u003cem\u003ePadma\u003c/em\u003e) and a single potato rootstock (Granola). While this limited scope allowed detailed characterization, it precludes broad generalization. The starkly contrasting outcomes between the two scion varieties synergistic with \u003cem\u003ePadma\u003c/em\u003e versus neutral/competitive with \u003cem\u003eThilina\u003c/em\u003e, underscore that scion-rootstock compatibility is highly specific, and without screening additional cultivars, the optimal combinations for this system remain largely unknown.\u003c/p\u003e\n \u003cp\u003eThe experimental design also contained constraints that limit mechanistic interpretation. The absence of key experimental controls, specifically self-grafted (homograft) controls (tomato-on-tomato, potato-on-potato) and reciprocal grafts (potato scions onto tomato rootstocks), makes it impossible to distinguish effects specifically attributable to heterografting from general responses to the grafting process itself or to understand directionality in scion-rootstock interactions. Additionally, this study quantified phenotypic outcomes but did not measure underlying physiological processes. Interpretations regarding hormonal signaling such as gibberellin-mediated height suppression, enhanced resource acquisition, or source-sink dynamics remain speculative without supporting data on nutrient and water uptake efficiency, hormone profiles across the graft union, photosynthetic rates and assimilate partitioning, root system architecture, and tuberization signaling pathways. The study also did not evaluate whether potato rootstock confers disease resistance to the tomato scion or whether the composite plant shows altered susceptibility to pathogens affecting either component. Finally, although graft success rates were not systematically reported, variable replication numbers (ranging from 5 to 10 across measurements) suggest possible differential survival or sample loss that could influence results, and this omission limits assessment of the technique\u0026apos;s practical reliability.\u003c/p\u003e\n \u003cp\u003eTo address these limitations and advance this promising technique toward practical application, several research priorities are identified. Field validation trials across diverse agro-ecological zones in Sri Lanka are essential to assess environmental robustness, economic viability, and performance under real-world pest and disease pressure, and these should include both protected cultivation and open-field comparisons. Systematic evaluation of a broader portfolio of tomato scion varieties and potato rootstocks is needed to identify compatibility rules and discover optimally synergistic combinations. Investigations into physiological mechanisms using isotope tracing for assimilate partitioning, hormone quantification across the graft union, and root system characterization are necessary to understand the mechanistic basis of synergistic versus competitive interactions. Explicit challenge trials with major soil-borne pathogens would quantify whether potato rootstocks confer resistance benefits to tomato scions, which represents a key potential advantage for smallholder adoption. Systematic investigation of factors affecting graft success would improve technique reliability for extension dissemination, while cost-benefit analysis comparing heterografting to conventional separate cultivation is essential to determine economic viability for smallholder farmers. Finally, studies extending beyond single-season evaluations to assess perennial performance or ratoon cropping potential would determine whether heterografted plants offer multi-season productivity benefits.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions and Recommendations","content":"\u003cp\u003eThis study provides evidence that heterografting tomato scions onto potato rootstocks is a technically feasible approach for integrated crop production under controlled environmental conditions. The cleft grafting method successfully produced functional composite plants capable of yielding both tomato fruits and potato tubers simultaneously. The most significant finding is the scion-dependent nature of system productivity. The Granola/Padma combination demonstrated synergistic potential, with substantial increases in both tomato fruit yield (approximately 2.8-fold) and potato tuber yield (approximately 2.1-fold) compared to non-grafted controls under the conditions tested. This yield enhancement was primarily driven by increased number of reproductive sinks (fruits and tubers) rather than increased individual organ size, and these productivity gains were achieved without compromising fruit quality and with only minor delays in harvest timing of five to nine days.\u003c/p\u003e \u003cp\u003eHowever, these promising results must be interpreted within the study's limitations. The contrasting performance of the Granola/\u003cem\u003eThilina\u003c/em\u003e combination, which showed enhanced tomato yield but suppressed tuber production, demonstrates that positive outcomes are not universal but require specific scion-rootstock compatibility. Furthermore, as a single-season controlled-environment study with a limited genetic sample and without critical experimental controls including self-grafted plants and reciprocal grafts, these findings should be considered a proof-of-concept requiring validation under diverse field conditions before widespread recommendation. Therefore, tomato-potato heterografting represents a promising model for vertical intensification that merits further investigation. The technique offers a potential pathway to enhance land-use efficiency in space-constrained agricultural systems, but its translation from research concept to practical application depends on addressing the knowledge gaps identified above.\u003c/p\u003e \u003cp\u003eFor researchers, it is recommended that future work prioritize field validation trials across multiple agro-ecological zones to establish environmental robustness, conduct mechanistic studies to elucidate hormonal and assimilate partitioning dynamics underlying scion-rootstock interactions, expand genetic screening to identify optimally compatible combinations and establish predictive compatibility criteria, and include appropriate controls such as self-grafted plants in future experimental designs. For agricultural extension services, it is advisable to monitor field validation outcomes before developing training materials, establish demonstration plots only after multi-location field data confirm consistent performance, and develop clear guidelines for graft success optimization based on systematic protocol research. For growers and smallholders, heterografting should be approached as an experimental technique requiring careful evaluation under local conditions, beginning with small-scale trials using the Granola/Padma combination which showed promise in this study, while maintaining realistic expectations regarding variability and the need for skill development in grafting technique and documenting local experiences to contribute to the collective knowledge base. For policymakers and research funders, support should be directed toward the priority research areas identified, particularly field validation and physiological mechanism studies, with recognition of heterografting as a long-term research and development investment rather than an immediately deployable technology, while facilitating collaboration between research institutions and extension services to ensure science-based technology transfer. In summary, this study establishes a foundation for understanding tomato-potato heterografting as a potential intensification strategy, and realizing this potential will require sustained, systematic research to transform these preliminary findings into reliable, science-based recommendations for agricultural practice.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003e \u003cb\u003eCompeting interests\u003c/b\u003e:\u003c/strong\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThe authors did not receive support from any organization for the submitted work.\u003c/p\u003e\u003ch2\u003eAuthor Contributions:\u003c/h2\u003e \u003cp\u003eConceptualization: K.M.R.D. Abhayapala; Methodology: K.M.R.D. Abhayapala and P.D. Abeythilakarathe; Formal analysis and investigation: K.M.R.D. Abhayapala, A.A.L.C. Perera, and P.N.M.S. Piyarathne; Writing - original draft preparation: K.M.R.D. Abhayapala, A.A.L.C. Perera, and P.N.M.S. Piyarathne; Writing - review and editing: K.M.R.D. Abhayapala; Supervision: K.M.R.D. Abhayapala and P.D. Abeythilakarathe\u003c/p\u003e\u003ch2\u003eData Availability:\u003c/h2\u003e \u003cp\u003eAll data are presented in the manuscript in summarized form. Raw data are available upon request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAsseng S, Cammarano D, Basso B, Chung U, Alderman PD, Sonder K, Reynolds M, Lobell DB (2017) Hot spots of wheat yield decline with rising temperatures. Glob Change Biol 23:2464\u0026ndash;2472. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/gcb.13530\u003c/span\u003e\u003cspan address=\"10.1111/gcb.13530\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChandrasena DPN, Wathugala DL, Prematilake VA (2020) Evaluation of potato (\u003cem\u003eSolanum tuberosum\u003c/em\u003e L.) genotypes for resistance to bacterial wilt (\u003cem\u003eRalstonia solanacearum\u003c/em\u003e) in the upcountry of Sri Lanka. Potato Res 63:439\u0026ndash;453. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11540-020-09450-4\u003c/span\u003e\u003cspan address=\"10.1007/s11540-020-09450-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFAO (2017) The future of food and agriculture \u0026ndash; Trends and challenges. Food and Agriculture Organization of the United Nations, Rome\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFernie AR, Bachem CWB (2021) Metabolomics of potato\u0026ndash;plant development and its response to stress. Potato Res 64:301\u0026ndash;304. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11540-021-09515-w\u003c/span\u003e\u003cspan address=\"10.1007/s11540-021-09515-w\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGamelin FX, Baquet G, Berthoin S, Thevenet D, Nourry C, Nottin S, Bosquet L (2009) Effect of high intensity intermittent training on heart rate variability in prepubescent children. Eur J Appl Physiol 105:731\u0026ndash;738. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00421-008-0955-8\u003c/span\u003e\u003cspan address=\"10.1007/s00421-008-0955-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGisbert C, Prohens J, Raig\u0026oacute;n MD, Stommel JR, Nuez F (2011) Eggplant relatives as sources of variation for developing new rootstocks: effects of grafting on eggplant yield and fruit apparent quality and composition. Sci Hortic 128:14\u0026ndash;22. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scienta.2010.12.007\u003c/span\u003e\u003cspan address=\"10.1016/j.scienta.2010.12.007\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGoldschmidt EE (2014) Plant grafting: new mechanisms, evolutionary implications. Front Plant Sci 5:727. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3389/fpls.2014.00727\u003c/span\u003e\u003cspan address=\"10.3389/fpls.2014.00727\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKumar P, Lucini L, Rouphael Y, Cardarelli M, Kalunke RM, Colla G (2015) Insight into the role of grafting and arbuscular mycorrhiza on cadmium stress tolerance in tomato. Front Plant Sci 6:477. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3389/fpls.2015.00477\u003c/span\u003e\u003cspan address=\"10.3389/fpls.2015.00477\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKumar P, Lucini L, Rouphael Y, Cardarelli M, Kalunke RM, Colla G (2015) Insight into the role of grafting and arbuscular mycorrhiza on cadmium stress tolerance in tomato. Front Plant Sci 6:477. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3389/fpls.2015.00477\u003c/span\u003e\u003cspan address=\"10.3389/fpls.2015.00477\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKumar P, Pandey SK, Singh BP, Singh S, Singh D (2017) Heterografting in potato and tomato: A sustainable technology for enhancing productivity. Indian J Agric Sci 87:303\u0026ndash;311\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKyriacou MC, Rouphael Y, Di Gioia F, Kyratzis A, Serio F, Renna M, De Pascale S, Santamaria P (2017) Micro-scale vegetable production and the rise of microgreens. Trends Food Sci Technol 57:103\u0026ndash;115. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.tifs.2016.09.005\u003c/span\u003e\u003cspan address=\"10.1016/j.tifs.2016.09.005\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eObrero \u0026Aacute;, Lopera CS, Garc\u0026iacute;a MC (2020) The potential of interspecific grafting in horticulture: a review. Agronomy 10(11):1738. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/agronomy10111738\u003c/span\u003e\u003cspan address=\"10.3390/agronomy10111738\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePandey SK, Singh D, Singh BP (2017) Challenges and strategies for enhancing potato production in tropical and subtropical regions. In: Chakrabarti SK, Xie C, Tiwari JK (eds) The Potato Genome. Springer, Cham, pp 257\u0026ndash;272. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/978-3-319-66135-3_16\u003c/span\u003e\u003cspan address=\"10.1007/978-3-319-66135-3_16\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePrematilake VA, Gajanayake J, Bandaranayake PC (2018) Impact of root-knot nematode (\u003cem\u003eMeloidogyne incognita\u003c/em\u003e) on the growth and yield of tomato (\u003cem\u003eSolanum lycopersicum\u003c/em\u003e L.) in Sri Lanka. J Nat Sci Found Sri 46(4):429\u0026ndash;438. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.4038/jnsfsr.v46i4.8635\u003c/span\u003e\u003cspan address=\"10.4038/jnsfsr.v46i4.8635\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSavvas D, Colla G, Rouphael Y, Schwarz D (2010) Amelioration of heavy metal and nutrient stress in fruit vegetables by grafting. Sci Hortic 127:156\u0026ndash;161. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scienta.2010.09.011\u003c/span\u003e\u003cspan address=\"10.1016/j.scienta.2010.09.011\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSingh H, Kumar P, Chaudhari S, Edelstein M (2017) Tomato grafting: A global perspective. HortScience 52(10):1328\u0026ndash;1336. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.21273/HORTSCI11996-17\u003c/span\u003e\u003cspan address=\"10.21273/HORTSCI11996-17\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSlifka MK, Whitton JL (2000) Clinical implications of dysregulated cytokine production. J Mol Med. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s001090000086\u003c/span\u003e\u003cspan address=\"10.1007/s001090000086\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWishart J, George TS, Brown LK, Ramsay G, Bradshaw JE, White PJ, Gregory PJ (2013) Measuring variation in potato roots in both field and glasshouse: the search for useful yield predictors and a simple screen for root traits. Potato Res 56:245\u0026ndash;261. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11540-013-9240-2\u003c/span\u003e\u003cspan address=\"10.1007/s11540-013-9240-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"potato-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"potr","sideBox":"Learn more about [Potato Research](http://link.springer.com/journal/11540)","snPcode":"11540","submissionUrl":"https://www.editorialmanager.com/potr/default2.aspx","title":"Potato Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Double-cropping, Heterografting, Land-use efficiency, Protected cultivation, Solanum lycopersicum, Solanum tuberosum","lastPublishedDoi":"10.21203/rs.3.rs-9199706/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9199706/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study systematically evaluated the agronomic viability of a novel double-cropping system through heterografting between tomato (\u003cem\u003eSolanum lycopersicum\u003c/em\u003e L.) and potato (\u003cem\u003eSolanum tuberosum\u003c/em\u003e L.). Using cleft grafting, two determinate tomato scions (\u003cem\u003eThilin\u003c/em\u003ea and \u003cem\u003ePadma\u003c/em\u003e) were grafted onto the vigorous potato rootstock Granola under protected cultivation in Sri Lanka's up-country region. Results demonstrated a critical scion-specific interaction governing system productivity. The Granola/\u003cem\u003ePadma\u003c/em\u003e combination exhibited a greater compatibility, increasing tomato fruit yield by 2.8-fold and potato tuber yield by 2.1-fold per plant compared to non-grafted controls. Yield enhancement was exclusively mediated through a significant increase in the number of fruits and tubers, not their individual size. In contrast, the Granola/\u003cem\u003eThilina\u003c/em\u003e graft increased tomato yield but suppressed tuber initiation, highlighting a competitive interaction. Heterografting modified plant architecture, reducing height by 21\u0026ndash;24% while maintaining or enhancing leaf area, and caused only minor, agronomically insignificant delays in phenology with no detriment to fruit quality. These findings confirm that interspecific grafting within Solanaceae is a functionally viable intensification strategy. The synergistic Granola/\u003cem\u003ePadma\u003c/em\u003e graft establishes a scientifically validated model for dramatic land-use efficiency gains, leveraging complementary resource partitioning and source-sink balance to optimize productivity from a single plant, with direct applicability for smallholder systems.\u003c/p\u003e","manuscriptTitle":"Evaluating Tomato-Potato Heterografting for Enhanced Crop Performance in Sri Lanka","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-21 16:43:57","doi":"10.21203/rs.3.rs-9199706/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2026-04-19T05:25:17+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-14T10:35:56+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Potato Research","date":"2026-03-25T09:39:30+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-25T04:31:50+00:00","index":"","fulltext":""},{"type":"submitted","content":"Potato Research","date":"2026-03-24T12:22:25+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"potato-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"potr","sideBox":"Learn more about [Potato Research](http://link.springer.com/journal/11540)","snPcode":"11540","submissionUrl":"https://www.editorialmanager.com/potr/default2.aspx","title":"Potato Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e96d55e6-0668-4ddd-8ae9-d10da7cad1b7","owner":[],"postedDate":"April 21st, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-21T16:43:57+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-21 16:43:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9199706","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9199706","identity":"rs-9199706","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}