Physiological Variation of Brassica Cultivars/Landraces during Seed Germination and Early Seedling Growth under Salt Stress

摘要

Physiological variations of fifteen Brassica juncea cultivars/landraces and a Brassica rapa landrace during germination and early seedling growth under salt stress were investigated. Percent germination, rate, vigour and threshold were evaluated. Salinity decreased the percent germination, rate, and vigour of two Brassica species, with considerable variation among cultivars/landraces. Relatively high thresholds, between 300 to 250 mM NaCl for inhibition of total germination were observed in B. junceacultivars of Indian origin i.e. 'RH 30', 'RH 8606', 'RH 9021', 'RH 9011' and 'Prakash'. The lowest thresholds were recorded in 'Common green', 'Ndakupuka' and 'Sani'. From the germination study, a relatively salt-tolerant B. juncea cv. 'Prakash', two B.juncea landraces 'Common green' and 'Ndakupuka' and a relatively salt-sensitive B. rapa landrace 'Sani' were selected for salinity tolerance assessment at the seedling stage. The growth of 'Common green', 'Ndakupuka', 'Prakash', and 'Sani' was retardedwith increasing salinity reducing the leaf area of all tested cultivars. Salinity caused an accumulation of Na~+ ions and a decrease of K~+, Ca~(++) and Mg~(++) ions in the shoots of the tested cultivars. Na~+ accumulation was highest in 'Sani' and lowest in 'Common green' at 175 mM NaCl. The K~+ content of the shoots in 'Sani' was lowest in treated and control samples. Likewise, the Ca~(++) content of shoots of 'Sani' seedlings treated with NaCl was low but higher than "Common green". The effect of NaCl on Mg~(++) was similar to that on Ca~(++). The results suggest that the higher relative growth reduction of 'Sani' may be correlated with higher Na~+ accumulation and lower K~+, Ca~(++) and Mg~(++) uptake under a saline environment. A physiological explanation is provided for salt stress tolerance in all tested cultivars and landraces.