Response of Citrus to Exogenously Applied Salicylate Compounds during Abiotic and Biotic Stress
Citrus is exposed to a number of abiotic and biotic stresses that limit its productivity. Exogenous application of salicylic acid (SA) can induce plant defense mechanisms against environmental stresses. We investigated the effect of exogenously applied SA in alleviating stress damage in citrus during heat, cold, and disease stresses. Sodium salicylate (Na-SA) reduced the electrolyte leakage percentage (ELP) in both heat (up to 84%) and cold (up to 20%) stressed plants and maintained cell integrity of citrus leaves. However, the protective effect of Na-SA was concentration dependent with lower (<0.08 mM) and higher (>0.20 mM) concentrations failing to induce heat or cold tolerance. A narrow concentration range of 0.10 to 0.16 mM was most effective in protecting citrus from heat and cold stresses. Application of 0.14 to 0.18 mM Na-SA to Huanglongbing (HLB) -infected citrus trees increased plant pH from 6.1 to 6.5 compared to the untreated control. Salicylic acid applied to HLB-infected citrus trees also induced new foliage growth and flowering. Collectively, our results suggest that SA applied at appropriate concentrations can alleviate heat, cold, and disease stresses in citrus. In addition, appropriate concentrations of SA can be used to regulate the young foliage emergence and flowering in HLB infected citrus trees to compensate for the severe defoliation and regulate plant metabolic processes. Abbreviations: ELP Electrolyte leakage percentage; HLB Huanglongbing; K-SA Potassium Salicylate; Na-SA Sodium Salicylate; SA Salicylic acid.