Abstract
The influence of water deficit on water content (WC), total soluble solids (TSS), osmotic potential (OP), sugar content and osmotic adjustment (OA) of expanded and partly expanded leaves of Brassica oilseeds was examined. Nine canola (B. napus) cultivars (Karoo, Monty, Pinnacle, Hyden, Mystic, Rainbow, Surpass 300, Surpass 400, Surpass 501), two doubled haploids, one from Karoo (KDH) and the other from Monty (MDH) and one line of Indian mustard (B. juncea, PI-81792) were grown under glasshouse and net-house conditions. Expanded wilted leaves of Karoo and Monty absorbed excessive amounts of water per dry weight upon in vitro rehydration compared with control non-stressed leaves, resulting in underestimation of OA calculated on the basis of the relative water content (RWC). Hence, estimation of OA based on water weight per leaf dry weight (WC) was preferred. Young expanding leaves maintained visual turgor for 6-7 d after withholding irrigation, while expanded leaves on the same plants ceased to regain turgor overnight. The young expanding leaves exhibited greater accumulation of TSS and, consequently, more negative OPs compared with expanded leaves. Maintenance of OA after irrigation and turgor recovery was evident in both expanded and expanding leaves. Although OA under drought and upon turgor recovery varied within cultivars in different experiments, outstanding OA capacity, in terms of both magnitude and stability, was identified in the cultivar Hyden and in the doubled haploid of Monty, indicating the potential to select for this trait as well as to exploit variability for OA through haploidization. Key words: Brassica oilseeds, drought stress, osmotic adjustment, haploid lines
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