Understanding the effect of heat stress during seed filling on nutritional composition and seed yield in chickpea (Cicer arietinum L.)

Increasing temperature affects all food crops, thereby reducing their yield potential. Chickpea is a cool-season food legume vital for its nutritive value, but it is sensitive to high temperatures (> 32/20 °C maximum/minimum) during its reproductive and seed-filling stages. This study evaluated the effects of heat stress on yield and qualitative traits of chickpea seeds in a controlled environment. Chickpea genotypes differing in heat sensitivity [two heat-tolerant (HT) and two heat-sensitive (HS)] were raised in pots, initially in an outdoor environment (average 23.5/9.9 °C maximum/minimum), until the beginning of pod set (107-110 days after sowing). At this stage, the plants were moved to a controlled environment in the growth chamber to impose heat stress (32/20 °C) at the seed-filling stage, while maintaining a set of control plants at 25/15 °C. The leaves of heat-stressed plants of the HT and HS genotypes showed considerable membrane damage, altered stomatal conductance, and reduced leaf water content, chlorophyll content, chlorophyll fluorescence, and photosynthetic ability (RuBisCo, sucrose phosphate synthase, and sucrose activities) relative to their corresponding controls. Seed filling duration and seed rate drastically decreased in heat-stressed plants of the HT and HS genotypes, severely reducing seed weight plant^-1 and single seed weight, especially in the HS genotypes. Yield-related traits, such as pod number, seed number, and harvest index, noticeably decreased in heat-stressed plants and more so in the HS genotypes. Seed components, such as starch, proteins, fats, minerals (Ca, P, and Fe), and storage proteins (albumin, globulins, glutelin, and prolamins), drastically declined, resulting in poor-quality seeds, particularly in the HS genotypes. These findings revealed that heat stress significantly reduced leaf sucrose production, affecting the accumulation of various seed constituents, and leading to poor nutritional quality. The HT genotypes were less affected than the HS genotypes because of the greater stability of their leaf water status and photosynthetic ability, contributing to better yield and seed quality traits in a heat-stressed environment.