Biochemical markers in the assessment of abiotic stress tolerance in Cucurbita plants

The purpose of this study was to compare biochemical stress markers in leaves of Cucurbita maxima (14), C. moschata (11), and C. pepo (11) accessions grown in stressed (drought) and non-stressed conditions (optimal irrigation). The expected intra- and interspecific variability may suggest the potential of these markers as tools for pre-breeding Cucurbita plants for improved abiotic stress tolerance. The proposed biochemical markers of stress, analyzed in the leaves of open-field grown plants (at the generative phase of the development), included lipid peroxidation intensity (LP, a proposed marker of oxidative stress and membrane integrity), proline content (Pro, a proposed marker of drought stress), reduced glutathione content (GSH, a proposed marker of abiotic stress tolerance), total phenolic compounds content (TP), and activity of an antioxidant enzyme - superoxide dismutase (SOD). There was a significant variability in foliar contents of Pro (0.5-8.7 mg/g dry weight) and GSH (1.7-5.7 mg/g fresh weight), as well as LP (38.0-155.7 nmol/g f.w.), among the tested species and accessions. C. maxima accessions had a lower change in Pro content between control and stressed plants, contrary to C. moschata accessions, which also had higher LP in both control and stressed plants when compared to the other two species. SOD activity was invariable in all investigated plants (0.5-0.7 U/mg f.w.). Almost all accessions accumulated lower content of TP (10.5-22.9 mg/g d.w.) in leaves of stressed plants compared to respective controls (up to 1.8-fold lower). The results suggest that tested biochemical stress markers, except SOD, might be used to investigate abiotic stress tolerance in Cucurbita plants. Bearing in mind that the number of publications that report similar experiments in Cucurbita species grown in open field conditions are rather scarce, as well as the fact that the improved varieties require multi-year experimental data, the presented findings could provide a preliminary contribution to research focused on mitigating the effects of abiotic stress in these vegetables.