Tolerance and Osmoregulation of Pumpkin Cultivars Exposed to Water Deficit

Pumpkin (Cucurbita spp.) is a vegetable of great socioeconomic importance for the Brazilian semi-arid region, but its production faces challenges due to adverse edaphoclimatic conditions. Environmental stresses, such as water deficit, are limiting factors during seed germination and plant establishment. Therefore, this study aimed to select pumpkin cultivars that are more resistant when subjected to water deficit. The experiment was conducted in a completely randomized design, with four replicates of 25 seeds, in a 3 × 6 factorial scheme, combining three levels of water deficit (0.0, -0.15, and -0.3 MPa of polyethylene glycol, PEG 6000) and six Cucurbita spp. cultivars, including five pumpkin cultivars (“Tetsukabuto”, “Soberana”, “Kin”, “Bahiana Tropical”, and “Sergipana”) and one zucchini cultivar (“Adele”). The evaluated variables included germination, germination speed index, shoot and root length, shoot and root dry mass, total free amino acids, proline, total soluble sugars, and citrulline. The data were analyzed and subjected to cluster analysis and variance analysis compared by the Scott-Knott test (P ≤ 0.05). Water deficits of -0.15 and -0.3 MPa affect the initial growth of pumpkin cultivars, with negative impacts on germination, growth, biomass accumulation, and cellular osmotic homeostasis. The “Adele” cultivar stands out as the most tolerant to the -0.15 MPa water deficit, while “Tetsukabuto” is the most sensitive. Water deficit tolerance in pumpkins is related to the ability to accumulate metabolites such as proline, soluble sugars, and amino acids.