Variation in carbon isotope discrimination and its relationship with harvest index in the reference collection of chickpea germplasm

Terminal drought is a major constraint to chickpea productivity. Carbon isotope discrimination (C-13), an integrator of plant behaviour influencing transpiration efficiency (TE), is an important component of yield under drought. The variation in C-13 and its association with yield was assessed in the reference collection of chickpea germplasm. Drought stress reduced shoot biomass by 36-39% and grain yield by 23%. Mean C-13 was low and the range of genetic variation was high under drought stress. Largely, high C-13 accessions were early in flowering (40-50 days), moderate in shoot biomass, high in seed yields and high in harvest index (HI). C-13 was positively correlated with seed yield in both the years under drought stress, only in 2008-09 under optimal irrigation. This positive association was very close with HI. Among the yield components, C-13 was closely associated with pod numbers per unit area and seed size under drought stress. Path coefficients showed no direct association of C-13 with grain yield but an indirect negative association through shoot biomass at maturity and a close positive association through HI. The closest association of HI or shoot biomass was seen in the maturity group of accessions that experienced the optimum terminal drought stress.