ABSTRACT Alkalinity is one of the main limiting factors of seed germination in alkaline soils. The aim of this study was to evaluate the effects of Na2CO3 levels (0, 5, 10, 15, 20 and 25 mM) on seed germination, seed reserve utilization and seedling vigour of three local bitter vetch cultivars (Buinzahra, Shahreza and Tarom). The results indicated that increasing Na2CO3 concentrations caused a decrease in germination percentage (GP), germination rate (GR), seedling length, seedling dry weight (SLDW) and seed reserve utilization efficiency (SRUE). The rate of reduction in shoot length in comparison with the control in different concentrations of Na2CO3 was detected from Buinzahra as 30-92%, Shahreza 39-97% and Tarom 13-83%. Decrease in root length was more than shoot length in all the cultivars at each Na2CO3 level, as compared to the control. The weight of mobilized seed reserve (WMSR) and seed reserve depletion percentage (SRDP) decreased with increasing Na2CO3 levels up to 10 mM in Buinzahra and Tarom cultivars and up to 15 mM in Shahreza. WMSR and SRDP then rapidly raised with higher alkalinity levels. These results suggest that reduction of seed germination and decline in seedling dry weight in response to alkalinity stress is a consequence of decline in seed reserve utilization efficiency.
