The effect of NaCl on the germination and early seedling growth of white clover (Trifolium repens L.) populations selected for high and low salinity tolerance

Abstract

Salt tolerance at germination and seedling emergence was examined in three populations of white clover (Trifolium repens L.) (cv. Haifa and two lines derived from cv. Haifa, ('Low Cl S2' and 'High Cl S2')) which differed significantly in salt tolerance as mature plants. For all three populations, germination decreased significantly (p < 0.001) with increasing NaCI concentrations between 60 to 200 mol m -3 NaCl, but there were no differences in relative germination between the three populations at any salinity level. Percentage germination began to decrease at 60 mol m -3 NaCl, was reduced to 50% of the viable seeds at 145 mol m -3 NaCl and less than 20% of the seeds that germinated at 0 mol m -3 NaCl germinated at 200 mol m -3 NaCl. Rates (or time taken to achieve 50% germination) increased significantly (p < 0.001) with increasing NaCI concentration and there were significant differences (p<0.05) between populations. Seedling emergence was significantly more sensitive to NaCI than was germination. The threshold concentration for a reduction in seedling emergence was 10 mol m -3 NaCl, and seedling emergence was reduced by 50% at 60 mol m -3 NaCl. Although there were no differences between populations in percentage emergence, populations did differ (p < 0.05) in the rate of scedling emergence, which, like germination, was significantly slower (p<0.001) with increasing NaCI concentrations. No seedlings in any population produced a trifoliolate leaf at concentrations greater than 60 mol m -3 NaCl. Individual seedling dry weights decreased significantly (p < 0.001) at concentrations greater than 10 mol m -3 NaCl, but there were no differences between populations. Concentrations of Na and Cl in the shoots did not differ between populations however, there were significant differences (p < 0.05) in concentrations of Na, but not Cl, between salinity levels. This study indicates that, in T. repens, there is not necessarily a close correlation between salt tolerance at one growth stage compared with another and that this should be considered when choosing plant selection criteria for salt tolerance.