Improving the Biochemical and Physiological Wheat Processes by Foliar Application of Fulvic Acid Under Natural and Heat Stress Conditions

Abstract

Terminal heat stress under varying climatic conditions induces a significant reduction in yield by impacting the fertilization and grain filling. The use of biostimulants would be useful to boost terminal heat stress in the wheat crop. The research attempts to modulate the effect of heat stress on wheat by foliar application of fulvic acid. The wheat crop was exposed to high-temperature stress (3-5°C higher than ambient temperature) during booting and grain initiation under field conditions by staggering heat stress in the main plot. Various amounts of fulvic acid, i.e. water spray, 1,25, 2,50 and 3,75 mg L-1, were added under natural and heat stress conditions at booting and grain initiation stages of wheat crop. Heat stress during booting and grain filling phases significantly reduced chlorophyll a activity up to 32.58% and 25.44%, Chl b activity up to 31.48% and 20.37%, grain filling duration up to 42.43% and 20.81% and grain yield up to 45.47% and 36.79% but improved antioxidants viz Superoxide dismutase activity up to 31.74% and 22.29%, Total soluble protein activity up to 6.63% and 11.77%, Catalase activity up to 114.73% and 55.03%, Peroxidase activity up to 63.61% and 39.39%. The impact at the booting stage was more pronounced than at the grain-filling stage.  Application of fulvic acid @ 3.75 mg L^-1 and 2.50 mg L-1 during heat stress during booting and grain filling processes greatly increased chlorophyll, antioxidants, and grain yield relative to water spray and 1.25 mg L^-1 fulvic acid. The results suggest that foliar application of fulvic acid during heat stress induces thermotolerance in wheat positively impacting the physiology and biochemical processes.