Water scarcity is a major constraint limiting grain legume production particularly in the arid and semi-arid tropics. Different climate models have predicted changes in rainfall distribution and frequent drought spells for the future. Although drought impedes the productivity of grain legumes at all growth stages, its occurrence during reproductive and grain development stages (terminal drought) is more critical and usually results in significant loss in grain yield. However, the extent of yield loss depends on the duration and intensity of the stress. A reduction in the rate of net photosynthesis, and poor grain set and grain development are the principal reasons for terminal drought-induced loss in grain yield. Insight into the impact and resistance mechanism of terminal drought is required for effective crop improvement programmes aiming to improve resistance to terminal drought in grain legumes. In this article, the impact of terminal drought on leaf development and senescence, light harvesting and carbon fixation, and grain development and grain composition is discussed. The mechanisms of resistance, management options, and innovative breeding and functional genomics strategies to improve resistance to terminal drought in grain legumes are also discussed.

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Drought is one of the most important abiotic stresses constraining crop productivity worldwide. The objective of the present study was to investigate the differences in drought tolerance at leaf and stomatal level of black gram (genotypes: T9, KU 301, PU 19, USJD 113) and green gram (genotypes: Pratap, SG 21–5, SGC 16, TMB 37). Drought was applied for fifteen consecutive days at flowering stage (35 days after sowing). Mid-day leaf water potential (ΨL), leaf area, photosynthesis rate (PN), leaf chlorophyll, stomatal conductance (gs) and seed yield of drought- treated plants were calculated relative to those of well watered plants. Stomatal characteristics were observed in terms of stomatal frequency (SF) and stomatal aperture size (SA). Among the studied genotypes, T9 (black gram) and Pratap (green gram) proved their better tolerance capacity to drought by maintaining higher leaf area, ΨL, PN, leaf chlorophyll, gs and SA which contributed to better seed yield. Between the two crops, green gram appeared to be affected to a greater extent, as it experienced higher reduction in yield than black gram. A highly significant positive correlation (level 0.01) of seed yield was obtained with leaf area, ΨL, PN, leaf chlorophyll, gs and SA, whereas SF was found to be poorly correlated with seed yield.

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