Genetic Variation and the Relationships Among Growth, Morphological, and Physiological Traits in Pterocarpus macrocarpus: Implications for Early Selection and Conservation

Understanding genetic variation in commercially vital tree species is critical for optimizing breeding and conservation strategies. This study evaluates genetic variation, heritability, and trait correlations in Pterocarpus macrocarpus, a high-value hardwood central to Thailand’s reforestation efforts. We assessed growth (height, diameter), morphological (biomass dry weight, specific leaf weight), and physiological traits (net photosynthesis [A], transpiration rate [E], water-use efficiency [WUE]) across 112 open-pollinated families from six natural populations under controlled nursery conditions over 30 weeks. Using a randomized complete block design, variance and covariance analyses were conducted to estimate genetic parameters. Seedling survival reached 95%, confirming favorable conditions for genetic expression. Populations and families within populations exhibited significant divergence in growth and biomass traits, while physiological traits showed pronounced family-level variation (A, E, WUE) and population effects for WUE only. Residual variance dominated across traits, highlighting substantial within-family variation. Growth and biomass traits demonstrated moderate to high heritability (individual: 0.386–1.000; family: 0.614–0.895), whereas specific leaf weight and shoot-to-root ratio displayed lower individual heritability. Physiological traits exhibited low to moderate heritability (individual: 0.256–0.428; family: 0.473–0.615), with maternal effects (via seed weight) significantly influencing early growth. Height heritability declined over time, contrasting with stable diameter heritability. Strong genetic correlations among growth and biomass traits suggest potential for simultaneous selection gains. Physiological traits, however, exhibit weak or no correlation with growth, highlighting their independent genetic regulation. Population-level variation in growth and WUE may illustrate adaptive responses to seed-source environments. Our findings support nursery-based screening as a cost-effective tool for the early selection of superior families. WUE serves as a promising target for breeding programs focused on drought-prone sites. This study provides foundational insights for advancing P. macrocarpus genetic improvement and conservation, emphasizing the integration of physiological traits into breeding and conservation strategies.