Physiological and biochemical responses of the waterlogging-tolerant pumpkin resources to waterlogging stress.

• Both membership function classification method and principal component analysis comprehensive evaluation method can be used to evaluate the waterlogging tolerance of pumpkin resources. • Of the 27 pumpkin germplasm, 20 were evaluated as MWT, 4 as WT, and 1 each as HWT, WS, and HWS. • The water-resistant pumpkin can maintain the balance of reactive oxygen synthesis and removal, the membrane peroxidation degree is low, and more chlorophyll can be synthesized to resist stress. This study used 27 Chinese pumpkin resources for the waterlogging treatment and analyzed 16 growth and physiological indicators, including plant height and stem diameter. The waterlogging-tolerant and waterlogging-sensitive pumpkin resources were selected using the membership function grading method and principal component analysis. The changes in the biochemical indicators of pumpkins under waterlogging stress were also studied. The results showed that among the 27 pumpkin resources, five were waterlogging-tolerant materials ('013-2′, 'Changyi', 'Universal female parent', '450′, and 'Changer'), two were waterlogging-sensitive materials ('063-2′ and '367-2′), and the remaining were moderately tolerant to waterlogging. Waterlogging stress increased the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) and the contents of proline and pyruvate in pumpkins, which were higher in waterlogging-tolerant pumpkins than in waterlogging-sensitive ones. The malondialdehyde content of the waterlogging-tolerant pumpkins was lower than that of the waterlogging-sensitive ones. The alcohol dehydrogenase (ADH) and pyruvate dehydrogenase complex (PDC) activities in the root of waterlogging-tolerant pumpkins showed an upward trend, while the lactate dehydrogenase (LDH) activity showed an initial downward trend and then upward trend. The ADH, PDC, and LDH enzyme activities of the waterlogging-sensitive pumpkins increased initially and then decreased. The contents of chlorophyll a, chlorophyll b , total chlorophyll, and carotenoids in the waterlogging-sensitive pumpkins decreased, while those of the waterlogging-tolerant pumpkins increased. Additionally, waterlogging-tolerant pumpkins could maintain a good balance between the synthesis and clearance of reactive oxygen species, with a low degree of membrane lipid peroxidation, and synthesize more chlorophyll to resist waterlogging stress. The waterlogging-tolerant pumpkins mainly underwent ethanol fermentation in the early stages of waterlogging stress, followed by combined ethanol and lactic acid fermentation. However, the waterlogging-sensitive pumpkins mainly underwent lactic acid fermentation in the early stages of waterlogging stress. These findings provide a basis for the research on the waterlogging tolerance mechanism of pumpkins and the selection of the rootstock varieties of edible waterlogging-tolerant pumpkins. [ABSTRACT FROM AUTHOR]