Photosynthetic and yield performance of wheat (Triticum aestivum L.) under sowing in hot environment

Heat stress during the post-flowering and grain development stages is a key abiotic stress influencing grain yield in wheat (Triticum aestivum L.). In this study, 64 wheat genotypes, in their terminal growth stage, were subjected to two field temperatures caused by delayed sowing in two consecutive growing seasons. Results of photosynthetic gas exchange, chlorophyll fluorescence, yield attributes, and grain yield investigations were subjected to combined analysis of variance, which revealed significant differences in the 1000 grain weight (GW), grain filling duration (GFD), grain yield, gas exchange parameters, and maximum quantum efficiency PSII photochemistry (Fv/Fm) among the genotypes (G) between the normal and heat stress conditions (E) and G x E interactions. Heat stress accelerated reproductive phases and shortened GFD leading to lower GW and grain yield. Exposure to heat stress resulted in significant decreases in net CO2 assimilation rate (P-N), stomatal conductance (gs), transpiration rate (E), iWUE, WUE, Fv/Fm ratio, and yield, while it increased sub-stomatal CO2 concentration (C-i). Moreover, grain yield was found to be strongly correlated with C-i, Fv/Fm, and P-N. Path coefficient analysis and stepwise multiple regression revealed that greater improvements will be achieved in C-i and Fv/Fm by increasing yield and P-N performance when wheat is bred for tolerance to heat stress than those achieved by breeders under normal growing conditions.