Effect of individual and combination of heat and drought stress in maize at reproductive and grain filling stage

Increased occurrences and severity of heatwaves and drought events due to climate change are posing significant threat to crop productivity worldwide. Maize is one of the most important cereal crops used as food and animal feed. Heat and drought stress are major constraints for maize production. However, interaction effect of these two stresses in the field level is poorly understood. In this study, we have used a set of 20 maize genotypes with varying yield and biomass traits, which were exposed to heat and drought stress under field condition at reproductive and critical grain filling stage. Both heat and drought stress significantly reduced chlorophyll content (20-55%), relative water content (25-40%) and photosynthesis (34-48%) across the genotypes, with an additive effect observed under heat + drought combination. While both heat and drought stress significantly reduced biomass and cob weight, a combination of heat + drought resulted in significantly higher decline in yield (32 to 64%) across the genotypes. Interestingly, genotype VL-108,722-B-14-1-BB showed resilience of stress, by maintaining a robust root system, higher assimilation, that eventually resulted in higher biomass and yield under stress. Indeed, yield showed a significant positive correlation with root length (r = 0.77), root surface area and root volume (r = 0.66). Our study demonstrates that simultaneous occurrence of heat and drought stress is deleterious to maize growth and yield. Further studies at the molecular level would explain mechanistic basis of heat and drought stress resilience mechanism in maize.