Moringa oleifera leaf extract as a biostimulant on growth and other physio-chemical attributes of rubber (Hevea brasiliesnsis) under drought and heat stress conditions

Drought and high temperature are the major impediments limiting growth of Hevea. We studied the efficacy of foliar applied Moringa (Moringa oleifera) leaf extract (MLE) as a biostimulant on the response of Hevea to sub-optimal climatic conditions. Rubber plants of clone RRISL 203 cultivated in the Intermediate Zone (IZ) and Dry Zone (DZ) were spray treated with water (mock treatment), MLE at 5, 10 and 15% concentrations for IZ and 3 and 5% for DZ. Physiological parameters viz. net photosynthesis (Pr), chlorophyll content (Cc), stomatal conductance (gs) and leaf water potential (Ψ) were recorded after three months from the commencement of treatments whilst girth measurements were recorded at three and twelve months after treatments in the IZ. Total phenolic content (TPC) and antioxidant activities, employing FRAP (ferric reducing assay power) and ABTS (2,2’-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid) techniques, were estimated after three months from first spraying in the DZ. Significantly higher Pr, Cc and gs values were recorded from plants treated with MLE at all three concentrations as compared to control. Significantly higher TPC values (17.17 and 15.90 mg of gallic acid equivalent/ g of leaf sample), and FRAP values (14.79 and 14.70 mg of trolox equivalent/g of leaf sample) and ABTS values (70.26 and 59.43 mg of TE/g of leaf sample) were recorded in plants treated with MLE at both concentrations (3 and 5%) as compared to control (12.50 mg of GAE/g of leaf sample, 10.68 mg of TE/g of leaf sample and 49.96 mg of TE/g of leaf sample), respectively. A significantly higher girth (11.5 cm) was recorded in plants treated with MLE at 5% as compared to control (9.66 cm) after 12 months of treatments. Improved growth and physio-chemical attributes of rubber plants could be attributed to the beneficial effect of MLE as a biostimulant and therefore, exogenous application of MLE could effectively be utilized as an environmental friendly and inexpensive strategy for growth improvement in Hevea under sub-optimal climatic conditions.