Efficacy of Exogenous Sodium Nitroprusside, Salicylic Acid and Moringa (Moringa oleifera) Leaf Extracts as Biostimulants on Growth and Physiological Attributes of Rubber (Hevea brasiliensis) under Sub-optimal Climatic Conditions

Abstract

Stress phenomena that coincide, such as drought and heat, have been shown to affect the growth of
rubber (Hevea brasiliensis) negatively under sub-optimal climatic conditions in nontraditional drier
areas of Sri Lanka. Exogenous sodium nitroprusside (SNP), salicylic acid (SA), and moringa leaf
extract (MLE) as bio-stimulants have been shown to improve the growth and physiology of crop
plants under sub-optimal climatic conditions. Therefore, the present study aimed at exploring the
effect of the above bio-stimulants on the growth and physiology of rubber under sub-optimal climatic
conditions. Rubber plants of clone RRIC 121 cultivated in Hingurana, Ampara, Dry Zone (DZ) were
spray treated with SNP at 100 and 200 µM, SA at 0.1 and 0.2 µM, and MLE at 5, 10% concentrations
at monthly intervals for six months. Physiological parameters viz. chlorophyll content (cc), stomatal
conductance (gs), and leaf water potential (Ψ) were recorded before and after three months from the
commencement of treatments while growth measurements (girth and height) were recorded at three
and ten months of treatments. Significantly higher girth values were recorded in plants treated with
SNP, SA, and MLE at all concentrations compared to control and mock treatment after ten months
from the commencement of treatments. Significantly higher chlorophyll values were recorded in
plants treated with SNP at 100 µM (50.6±1.85), 200 µM (53.4±1.24), SA at 0.1 µM (49.5±1.49),
MLE at 5% (50.1±1.98) and 10% (51.1±1.35) concentrations compared to control (41.9±1.15) and
mock treatment (44.6±1.32) respectively after ten months from the commencement of treatments.
Significantly higher leaf water potential values were recorded in plants treated with SNP, SA, and
MLE at all concentrations compared to control and mock treatments after three months of the first
treatment. Significantly lower stomatal conductance values were recorded in plants treated with SNP
at 200 µM, SA at 0.1 and 0.2 µM, and MLE at 10% concentrations compared to control and mock
treatments after three months from the first treatment. Improved growth and physiological attributes
of rubber plants could be attributed to the beneficial effect of SNP, SA, and MLE as bio-stimulants.
Therefore, exogenous application of the above bio-stimulants may be utilized for growth
improvement in Hevea sp. under sub-optimal climatic conditions.

Keywords: Bio-stimulants, Growth, Physiological parameters, Rubber, Sub-optimal climatic conditions