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 × 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.

开花后和籽粒发育阶段的热胁迫是影响小麦籽粒产量的关键非生物胁迫（Triticum aestivumL.）。在这项研究中，64 种小麦基因型在其生长末期受到连续两个生长季节延迟播种导致的两个田间温度的影响。对光合气体交换、叶绿素荧光、产量属性和籽粒产量调查结果进行组合方差分析，发现千粒重（GW）、籽粒灌浆期（GFD）、籽粒产量、气体交换参数存在显着差异，以及在正常和热应激条件 (E) 和 G × E 相互作用之间的基因型 (G) 之间的最大量子效率 PSII 光化学 (Fv/Fm)。热应激加速了生殖阶段并缩短了 GFD，导致 GW 和谷物产量降低。暴露于热应激导致净 CO ₂同化率显着下降（P _N )、气孔导度 (gs)、蒸腾速率 ( E )、iWUE、WUE、Fv/Fm 比和产量，同时它增加了亚气孔 CO ₂浓度 ( C _i )。此外，发现谷物产量与C _i、Fv/Fm 和P _N密切相关。通径系数分析和逐步多元回归表明，与正常生长条件下的育种者相比，通过提高小麦的产量和P _N性能，在C _i和 Fv/Fm方面可以实现更大的改进。