Determination of salinity tolerance threshold in two rapeseed (Brassica napus L.) cultivars

Salinity effects on grain yield and some physiological characteristics of two rapeseed (Brassica napus L.) cultivars (Esteghlal and Talaye) were studied under saline conditions. Grain yield of cultivars was compared in a semi-controlled tested plots for two years. Six salinity levels were imposed on a silty loam soil using saline irrigation water. Electrical conductivity of irrigation water was 0.7, 6, 8, 10, 12 and 14 dS.m-1. Grain yield, yield components, harvest index (HI), relative water content (RWC), membrane instability (MIS), and leaf K:Na ratio reduced and leaf Na and Cl significantly (P< 0.01) increased in salinity treatments. Leaf K concentration showed a slight change with increasing salinity and the uptake antagonism between Na and K was not observed. Grain yield of Esteghlal severely decreased in salinity treatments. Relative salinity tolerance of these cultivars significantly correlated with plant height, branch number, siliques per plant, grain number.silique-1, leaf Na and leaf K:Na ratio. Results of this study revealed the relationship between leaf K:Na ratio, leaf sodium and relative salinity tolerance in these cultivarss. Relative grain yield of the cultivars were unaffected by soil salinity 4.8 dS.m-1 (ECe) in Talaye and Esteghlal. Each unit increase in salinity above the thresholds reduced the grain yield by 8.8% and 10.4% in Talaye and Esteghlal, respectively. Results of this experiment classified these two rapeseed cultivars in the moderately salt tolerant category.