Assessment of watermelon accessions for salt tolerance using stress tolerance indices

Abstract

Salt stress is the most significant constraint for agricultural production in arid and semi-arid regions. Thus, genetically improved stresstolerant varieties are needed for the future. The identification of salt-tolerant genotypes is the starting point for such breeding studies. This study was conducted to determine and assess the tolerance of different watermelon genotypes under saline conditions. Twenty-two watermelon genotypes and accessions were grown in pots with 3 kg of soil in four saline stress conditions (0 mmol kg(-1) as the control, 25, 50 and 100 mmol kg(-1) NaCl). The detrimental effects of salt stress on the plants were evident with increasing doses of NaCl. Stress indices calculated over the plant dry weights under the 100 mmol kg(-1) salinity level were used to assess the salt tolerance of the genotypes. Stress intensity was calculated as 0.76. Such a value indicated that the highest dose of salt exerted severe stress on the plants. The G04, G14 and G21 genotypes were considered to be salt tolerant, since these genotypes showed the highest values of K/Na and Ca/Na ratios in the plant tissue. The losses in dry mass at severe salt stress reached 75.48%. In principal component analyses, the genotypes had positive correlations with stress tolerance indices of MP (mean productivity), GMP (geometric mean productivity) and STI (stress tolerance index). The GMP and STI indices indicated that G04 (a member of Citrullus colocynthis), G14 and G21 could be prominent sources to develop salt tolerance.