Growth and physiological responses of cucumber (Cucumis sativus L.) to sodium chloride stress under solid hydroponics

Abstract

NaCl induced salinity stress has been studied for several years. However, development of salt tolerant cucumber has remained elusive partly due to lack of suitable screening system. Four cucumber genotypes (11411S and 11432S as salt tolerant whereas 11439S and HH1-8-57 as salt sensitive) were subjected to two levels of salinity (0 and 80 mM NaCl) under greenhouse conditions to determine the effect of salinity on growth, leaf gas exchange characteristics and cell membrane stability. The pre-germinated seeds of each genotype were sown in 1.6 L plastic pots filled vermiculite and peat in the ratio 2:1 (v/v). The pots were arranged in randomized complete block design with 15 seedlings per treatment replicated three times. The data on growth, survival, gas exchange characteristics was taken at the end of 21 days from the start of the experiment. Two cucumber genotypes, 11411S (salt tolerant) and 11439S (salt sensitive) were selected for the germination experiment. The germination was assessed at 5 salinity levels (0, 40, 60, 80,100 mM NaCl) and replicated five times. The germination percentage (GP), mean germination rate (MR) and mean germination time (MT) was recorded every 24 hours for 8 days. The data collected was subjected to standard analysis of variance using SAS statistical software and means separated by Dancun’s multiple range tests at P < 0.05. The results indicated that salt stress significantly reduced growth and survival rates of all cucumber genotypes but reduction in survival rate was severe in salt sensitive genotypes. Salinity significantly reduced photosynthetic rate, stomatal conductance, carboxylation efficiency, water use efficiency and transpiration rate of all genotypes but the decrease was higher in salt sensitive than tolerant cucumber genotypes. salinity did not affect the germination percentage but increased mean germination time especially of the salt sensitive genotype. We conclude that survival rate, photosynthetic rate and cell membrane stability can be used to assess salt tolerance in cucumber.