Abstract
Response of twenty-four onion (Allium cepa L.) genotypes to drought stress at thirty and fifty days after transplanting (DAT) was studied. Observations were recorded on relative water content (RWC), leaf osmotic potential (PSIos), gas exchange parameters, water use efficiency (WUE), carbon isotope discrimination, abscisic acid (ABA), leaf area and bulb yield. Significant differences were observed among the genotypes for all the parameters. The effect of drought stress was more critical at early stage of growth. Genotypes AK-649, AFLR and hybrid H-1 maintained the highest levels of RWC, PSIos, and leaf area under stress. Under stress bulb yield was highest in AK-649 at both stages of growth, while genotypes AN-650 and Sel-11 recorded lowest yield. AFLR showed the highest photosynthetic rate, followed by AK-649 and the lowest was recorded in Sel-11. Instantaneous and intrinsic WUE was highest in AK-649 and lowest in Sel-11. Carbon isotope discrimination values decreased under the influence of stress, AK-649 recorded the lowest under stress followed by S.Local. There was a marked increase in ABA content in AK-649, AFLR and hybrid H-1. The genotype with higher plant water status, higher ABA accumulation, and better WUE together with higher yield under stress are expected to be the most drought tolerant.
