Comprehensive evaluation of drought resistance of Melon (Cucumis melo L.) based on morphological and physiological...

Drought stress significantly inhibits melon seedling growth and ultimately reduces fruit yield. Consequently, identifying drought-resistant germplasms, elucidating the physiological and biochemical mechanisms underlying plant drought responses, and establishing reliable drought resistance evaluation indices are critical objectives for advancing drought-resistant breeding of melon.

This study measured 30 growth, physiological, and biochemical indices of melon seedlings under drought conditions. By integrating correlation analysis, cluster analysis, and regression analysis, the drought resistance of 15 melon germplasm resources were evaluated, and key drought resistance indices were identified. The results demonstrated that drought stress significantly reduced the dry and fresh weight, total root length, root surface area, root volume, root tips, and forks of melon seedlings, but significantly increased the root-shoot ratio of plants. Additionally, drought stress significantly reduced leaf relative water content (RWC), increased pigment content (chlorophyll a, chlorophyll b, carotene, and total pigment) and regulatory substance content (soluble sugar and γ-aminobutyric acid, GABA). Furthermore, drought stress elevated the levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and oxidized glutathione (GSSG), while reducing superoxide anion (O₂^·--) and GSH/GSSG, indicating oxidative stress in melon seedlings. Using D-value cluster analysis, the 15 melon germplasms were classified into 5 categories: strongly drought-resistant group (17Y1 and 17Y11), drought-resistant group (GT3, 23G36, YJM, 23G33 and 23G37), moderately drought-resistant group (GT4, 22P8 and GT1), drought-sensitive group (YD, TN and LB946), and highly drought-sensitive group (22P7 and 22G40). Stepwise regression analysis identified the following indices as objective evaluation criteria for melon seedling drought resistance: drought injury index (DI), chlorophyll a content, relative electrical conductivity (REC), and betaine content.

Taken together, this study screened 2 strongly drought-resistant melon materials, 5 drought-resistant materials, 3 moderately drought-resistant materials, 3 drought-sensitive materials and 2 highly drought-sensitive materials. At the same time, drought injury index (DI), chlorophyll a content, relative electrical conductivity (REC), and betaine content were selected as the drought resistance indices of melon. These findings lay a theoretical foundation for melon drought resistance breeding.