Influence of Drought Stress and Foliar Application of Salicylic Acid on Early Vegetative Stage of Cacao

Abstract

Cacao (Theobroma cacao L.) is noted to have a low tolerance to drought and is, therefore, not resilient to prolonged dry periods. The study sought to evaluate the morpho-anatomical and physiological responses of two clonal seedlings of cacao BR25 and K9 under drought stress and to explore the potential alleviating effects of salicylic acid (SA) at concentrations of 0.5 and 1.0 mM on the early vegetative stage. Eleven-month-old BR25 and K9 cacao were pre-treated with foliar application of 0.5 and 1.0-mM SA for 2 wk before the onset of drought conditions. Well-watered and drought seedlings with no pre-treatments served as the control. Water was withheld for 20 d, after which rewatering resumed for 3 mo. Results revealed that after 20 d of drought, both clonal varieties experienced a significant decline in relative water content (RWC) and increased ascorbate peroxidase (APX) and catalase activity. Changes in stem diameter were observed after a rewatering period of 3 mo. K9 exhibited a noticeable reduction in root and shoot dry weight and stomatal aperture after 20 d of drought, whereas BR25 showed a decrease in total chlorophyll content and chlorophylls a and b. Furthermore, the results of the study suggest that 0.5-mM SA has the potential to mitigate the drastic effects during drought in BR25 and K9 cacao by improving RWC, stomatal length, and width. On the other hand, 1.0- mM SA has the potential to alleviate the effects of drought experienced earlier on by improving root dry weight and APX activities of the seedlings.