Heat Stress at Reproductive Stage Disrupts Leaf Carbohydrate Metabolism, Impairs Reproductive Function, and Severely Reduces Seed Yield in Lentil

Rising temperatures or global warming will be detrimental for various crops. Moreover, because of increasing demand for lentil (Lens culinaris L.) grains, there is a need to broaden the adaptation of this crop into warmer climes. Hence, a study was conducted to evaluate the effects of high temperatures (>32/20oC) during reproductive growth on performance of lentil and to probe the mechanisms associated with reproductive failures. Three lentil genotypes, viz., LL699, LL931, and LL1122, were grown in pots at two sowing dates: (1) the normal sowing time (NS) in November so that day/night temperatures during the reproductive stage were below 32/20°C; and (2) late-sown (LS) in February so that temperatures during the reproductive stage were above 32/20°C. The plants were fully irrigated during both the sowing situations. In LS plants, the phenology was accelerated, leading to substantial reduction in biomass, flowers, and pods, accompanied by marked shortening of flowering period and podding duration, causing decreased seed yield. At the peak flowering stage (average temp. >32/23oC), the leaves of the LS plants had significantly lower relative leaf water content and lower stomatal conductance than NS plants at the same stage, indicating that the late sowing induced both water stress and heat stress. In LS plants, reproductive function was markedly reduced in all genotypes, causing increased pod abortion. The leaves of LS plants showed increased damage to membranes, chlorosis, decreased photochemical efficiency, with an associated reduction in sucrose synthesis and increase in its hydrolysis, compared with the NS plants. Heat stress, in combination with intermittent water stress during the reproductive phase in the LS plants, was extremely detrimental for all three lentil genotypes, with only minor differences among them. Controlled-environment studies, where the plants were subjected to high temperatures (33/15°C, 35/20°C) during reproductive growth, also validated the detrimental effects of heat stress on studied traits, similar to outdoor conditions.