Effects of Fertilization and Irrigation on Abiotic Stress and Antioxidant Markers in Leaves of Field-Grown Cucurbita maxima, C. moschata, and C. pepo

The main aim of this study was to evaluate the impact of contrasting irrigation and fertilization conditions on the most commonly tested markers of abiotic stresses: lipid peroxidation intensity (LP), proline (Pro), reduced glutathione (GSH) content, and total phenolics (TP) content in leaves of 25 genotypes of three Cucurbita species grown in an open field experiment. The experiment included unfertilized and non-irrigated, fertilized and non-irrigated, unfertilized and irrigated, and fertilized and irrigated treatments. Contrary to irrigated treatments, the intensity of LP was markedly higher in samples that were not irrigated (36.1–52.5%). For all C. moschata genotypes and most of the C. maxima and C. pepo genotypes, accumulation of Pro (0.7–3.0 mg/g) was higher in non-irrigated treatments, while GSH values were mostly higher in fertilized plants. The content of TP was higher in plants that were both irrigated and fertilized (8.6–38.4 mg/g GAE), reaching the highest values in C. pepo genotypes. The results indicate that irrigation has a greater impact on analyzed biochemical markers than fertilization in the early flowering phase of tested genotypes.