Fertilization Regimes in Huanglongbing-Infected Citrus latifolia Tan., and Its Physiological andHormonal Responses

Huanglongbing disease (HLB), caused by Candidatus Liberibacter asiaticus (CLas), affects all commercial citrus species. Persian lime (Citrus latifolia Tanaka), a crop of global economic importance, has shown tolerance to such disease. Efforts are therefore focused on prolonging the productive life of diseased trees through agronomic management. The objective of this study was to compare between healthy and HLB-affected Persian lime plants the effects of low (Ma-1), medium (Ma-2), and high (Ma-3) doses of macronutrients, in combination with treatments without the addition of micronutrients (Mi-1), using soil (Mi-2) or foliar (Mi-3) application. Treatments were applied every 18 days for one year. Even C. latifolia showed tolerance, HLB reduced its growth, chlorophyll content, and photosynthetic efficiency. In addition, it increased stem diameter of vascular bundles, reflectance in the visible spectrum, and the concentration of glucose, sucrose, starch, trans-cinnamic acid, benzoic acid, and salicylic acid in diseased plants. The hormonal response showed higher levels of benzoic acid and lower levels of salicylic acid than those reported in susceptible citrus. Those plants treated with low doses of macronutrients in combination with applying micronutrients to the soil (Ma-1+Mi-2) showed less effect of HLB with higher growth, chlorophyll concentration, and less starch accumulation. These results sug-gest that fractioning fertilizer application throughout the year might improve the efficiency of the agronomic HLB management and allow the reduction of the annual dose of fertilizers.