Osmotic adjustment, production, and post-harvest quality of mini watermelon genotypes differing in salt tolerance

The mini watermelon is a crop with high yield potential in the Brazilian semiarid region; however, some problems, such as the salinity of irrigation water, can cause physiological and biochemical changes in the species, compromising production and post-harvest quality of the fruits. In the present study, two genotypes of mini watermelon (Citrullus lanatus L.) cultivated in a hydroponic system were evaluated for the effects of nutrient solution salinity on yield, fruit quality, and solutes content. The experimental design used was completely randomized, in a factorial scheme (5 × 2), with four replicates, each consisting of three plants. The mini watermelon genotypes ‘Champagne’ (CP) and ‘Fancy’ (FY) were cultivated in nutrient solutions with different electrical conductivity levels - ECsol (2.5 - control, 3.5, 4.5, 5.5, and 6.5 dS m⁻¹). Production components, post-harvest variables of fruit quality and the contents of organic and inorganic solutes were evaluated. The increase in ECsol reduced the production variables, with the emphasis on the CP genotype, which stood out for comparatively mall production losses (45% - fruit mass); being considered tolerant to salt stress when compared to FY (57% - fruit mass). Fruit production showed a linear decrease, with a salinity threshold at 2.5 dS m⁻¹ in both genotypes. The salinity increased the contents of total soluble solids (TSS) in both genotypes: for 9.5 to 10.6 °Brix (11.6%) in the CP genotype and from 9.7 to 12.1° Brix (24.7%) in the FY. Contents of organic and inorganic solutes, except proline, can act as indicator for the selection of salinity-tolerant mini watermelon genotypes. Despite the changes induced by salt stress in the physicochemical characteristics, the fruits remained within acceptable commercial standards for both genotypes. The FY genotype, though salt-sensitive is more suitable for hydroponic cultivation up to ECsol of 4.5 dS m⁻¹, and both the genotypes can be used in systems up to with ECsol 6.5 dS m⁻¹.