Management of Spot Blotch and Heat Stress in Spring Wheat Through Azoxystrobin-Mediated Redox Balance

Abstract

Application of foliar fungicides for the management of spot blotch of wheat in South Asia is needed when the weather is extremely conducive to disease progression. Field experiments were conducted during two consecutive years 2014–2015 and 2015–2016 to evaluate the effect of fungicides in late-sown wheat which suffers from the combined stress of terminal heat and spot blotch. Azoxystrobin (125 g a.i./ha) when applied twice (ZGS 50 and ZGS 60) and thrice (ZGS 40, 50 and 60) was comparable and gave the best control. In two sprays, the area under disease progress curve (AUDPC) was reduced to 161 compared to 763 under unprotected. Application of fungicide maintained the leaf area under greenness, chlorophyll content and normalized difference vegetative index (NDVI) up to physiological maturity. The canopy temperature (CT) was also reduced in fungicide-treated plots. The positive effect of fungicide on increased days to maturity (11.5 days) contributed significantly to thousand kernel weight (TKW) and grain yield. The fungicide appeared to balance the level of reactive oxygen species like hydroxyl radicals (OH−) and superoxide radicals (O2−), reducing membrane damage and increasing antioxidants like superoxide dismutase (SOD), catalase (CAT). The application of azoxystrobin appeared to manage the terminal heat stress through redox balance and reduced the spot blotch resulted in enhanced grain yield.