Abstract
Response of four onion (Allium cepa L.) cultivars, viz., Arka Kalyan, Arka Niketan, Arka Pragathi, and PBR to water stress at 30 and 45 days after transplantation (DAT) was studied under pot culture conditions. Water stress treatments led to decline in leaf relative water content (RWC) and chlorophyll content in cv. PBR followed by Arka Pragathi. The electrolyte leakage under stress was high in cv. Arka Pragathi. The cv. Arka Kalyan exhibited stability in leaf RWC, electrolyte leakage, and chlorophyll levels under stress conditions at both growth stages. The changes in these parameters under stress were more evident at 30 DAT. Water stress led to an enhancement in abscisic acid (ABA) and decline in cytokinins, t-zeatin riboside (t-ZR) and dihydrozeatin riboside (DHZR) in the cultivars. The leaves of cv. Arka Kalyan followed by cv. Arka Niketan showed greater ABA accumulation under stress. Minimum ABA accumulation was recorded in the stressed plants of cv. PBR. Cytokinins t-ZR and DHZR contents in the stressed leaves were high in cvs Arka Kalyan and Arka Niketan compared to the other cultivars. The stress-induced changes in ABA were more apparent at 45 DAT and in cytokinins at 30 DAT. The bulb fresh and dry weights in the stressed plants were low in cvs PBR and Arka Pragathi, and high in cv. Arka Kalyan. The cultivar with higher ABA accumulation and lesser decline in cytokinins (t-ZR and DHZR) and chlorophyll contents together with lesser changes in electrolyte leakage under water stress would be relatively drought tolerant.
