Physiological alterations due to field salinity stress in melon (Cucumis melo L.)

This study was aimed to assess physiological responses of melon (Cucumis melo L.) cultivars to salinity stress under field conditions. Seventeen melon cultivars including 16 widely distributed native and one exotic ('Galia') were subjected to 2-year (2014-2015) field salinity stress. Leaf relative water content (RWC), membrane stability index (MSI), pigments [chlorophyll a, b, total chlorophyll (TChl), carotenoid (Car) and their ratios], malondialdehyde (MDA), H2O2 content, proline content (Pro), total soluble sugar content (TSC), salinity tolerance and susceptibility indices as well as yield were evaluated. The results of combined analysis of variance showed significant genotypic variation for all the traits and significant effect of salinity stress on all the traits with the exception of Chla/Chlb and TChl/Car ratios. Overall, field salinity stress caused an increase in leaf MDA, H2O2, Chla, Chlb, TChl, Car, Pro and TSC and caused a reduction in leaf MSI and RWC as well as yield. The results of correlation coefficients showed that accumulation of osmolytes (proline and TSC) led to an increase in RWC and a decrease in MDA contents. In addition, the results of multiple regression analysis showed that leaf MDA, TSC, MSI and Chla contents were the most important predictors of yield justifying 72% total variation of yield under saline conditions. These results may highlight a dynamic interplay among biomarkers for lipid peroxidation (MDA), sugar osmolytes (TSC) and photosynthetic pigment (Chla) to maintain cell viability and cell wall integrity under salinity stress conditions in melon.