Heat tolerance in spring wheat. II. Grain filling

Heat stress during grain filling is a major constraint to wheat (Triticum aestivum L.) yield. This study was performed to evaluate the relationship between stem reserves as a constitutive trait and of thermotolerance to sustained wheat grain filling under heat stress. Significant variation was seen among cultivars in the reduction in grain weight per ear (RGW), kernel number, and single kernel weight under heat stress. Differences in RGW among cultivars were ascribed to variation in the reduction in both kernel number and kernel weight under heat stress. Variation in the potential capacity for using mobilized stem reserves among cultivars was ascribed to variations in both kernel number and kernel weight under defoliation and ear shading. There was a strong negative correlation across cultivars (r = - 0.96; p ≤ 0.01) between RGW and PSR. A significant positive correlation (r = 0.92; p ≤ 0.01) was found across cultivars between the rate of chlorophyll loss under heat stress and photosynthate stem reserves (PSR) indicating that a high potential capacity for utilizing stem reserves for grain filling may be linked with accelerated leaf senescence. There was a strong negative association across cultivars between RGW and cell membrane thermostability at seedling (r =- 0.98) and the flowering (r = - 0.92; p ≤ 0.01) growth stages. The results indicate that grain filling under heat stress is closely related to the capacity for stem reserve remobilization as a constitutive trait and to plant thermotolerance as expressed by CMS in heat-hardened seedlings or adult plants.