Higher flower and seed number leads to higher yield under water stress conditions imposed during reproduction in chickpea

The reproductive phase of chickpea (Cicer arietinum L.) is more sensitive to water deficits than the vegetative phase. The characteristics that confer drought tolerance to genotypes at the reproductive stage are not well understood; especially which characteristics are responsible for differences in seed yield under water stress. In two consecutive years, 10 genotypes with contrasting yields under terminal drought stress in the field were exposed to a gradual, but similar, water stress in the glasshouse. Flower number, flower+pod+seed abortion percentage, pod number, pod weight, seed number, seed yield, 100-seed weight (seed size), stem+leaf weight and harvest index (HI) were recorded in well watered plants (WW) and in water-stressed plants (WS) when the level of deficit was mild (phase I), and when the stress was severe (phase II). The WS treatment reduced seed yield, seed and pod number, but not flower+pod+seed abortion percentage or 100-seed weight. Although there were significant differences in total seed yield among the genotypes, the ranking of the seed yield in the glasshouse differed from the ranking in the field, indicating large genotype×environment interaction. Genetic variation for seed yield and seed yield components was observed in the WW treatment, which also showed differences across years, as well as in the WS treatment in both the years, so that the relative seed yield and relative yield components (ratio of values under WS to those under WW) were used as measures of drought tolerance. Relative total seed yield was positively associated with relative total flower number (R2=0.23 in year 2) and relative total seed number (R2=0.83, R2=0.79 in years 1 and 2 respectively). In phase I (mild stress), relative yield of seed produced in that phase was found to be associated with the flower number in both the years (R2=0.69, R2=0.76 respectively). Therefore, the controlled drought imposition that was used, where daily water loss from the soil was made equal for all plants, revealed genotypic differences in the sensitivity of the reproductive process to drought. Under these conditions, the seed yield differences in chickpea were largely related to the capacity to produce a large number of flowers and to set seeds, especially in the early phase of drought stress when the degree of water deficit was mild.