Plant Growth and Mineral Element Content of Different Gourd Species and Watermelon under Salinity Stress

The watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] cultivar Crimson Tide and 7 different gourd genotypes [Cucurbita maxima, C. moschata, Luffa cylindrica, Benincasa hispida, Lagenaria siceraria landraces (Skp and Birecik), and L. siceraria hybrid (FRGold)] with rootstock potential for watermelon were grown under saline conditions (0, 4, 8, 12, and 16 dS m-1) to investigate the responses of the gourd genotypes and watermelon to 30 days of salt stress. Plant main stem length, shoot dry weight, root dry weight, reduction in shoot dry weight, concentration of Na+, Ca2+, and K+ in the leaves of the genotypes, and Ca2+/Na+ and K+/Na+ ratios were investigated. Plant length, and shoot and root dry weight of the plants significantly decreased as salinity stress increased. Gourd genotypes responded significantly differently to all investigated parameters under saline conditions. All genotypes had better growth performance than watermelon, except for L. cylindrica and B. hispida. The gourd genotypes and watermelon showed significant differences under saline conditions, with respect to ion regulation. Sodium concentration in the leaves of all the genotypes increased in response to salt application. There was a remarkable increase in Na+ concentration in the leaves of L. cylindrica, whereas the lowest Na+ concentration was observed in Birecik, and C. maxima, B. hispida, and L. cylindrica accumulated more Na+ than watermelon and the other gourd genotypes did under saline conditions. Ca2+/Na+ and K+/Na+ ratios were significantly reduced by salt treatment and the degree of decrease was dependent on genotype. Genotypes with higher Ca2+/Na+ and K+/Na+ ratios produced more dry weight. Significant positive correlations were observed between plant biomass parameters, and Ca2+/Na+ and K+/Na+ ratios, whereas strong negative correlations were observed between Na+ concentrations and shoot and root dry weight of the genotypes. Cucurbita and Lagenaria species were more tolerant to salinity stress than L. cylindrica, B. hispida, and watermelon.