Changes in ion (K, Ca and Na) regulation, antioxidant enzyme activity and photosynthetic pigment content in melon genotypes subjected to salt stress - a mixture modeling analysis

The present study aimed to identify the response of melon accessions and cultivars to salt stress in terms of ion exchange, enzyme activity, lipid peroxidation and photosynthetic pigment contents by mixture modelling. In mixture modeling, it is expected that the data set demonstrates a heterogeneous structure. This heterogeneity is characterized as unobservable heterogeneity. The data set’s heterogeneity produces severe deviations in the parameter assessments and the standard deviations. Heterogeneity is overcome when the data set separates itself into homogeneous sub-populations. Mixture modeling was performed using the Mclust mixture cluster program of the statistical software package R 5.2.3. Sub-populations were constructed by evaluating genotypes according to studied traits and correlation analysis was performed using the SPSS software package. The seedlings of 13 melon genotypes were harvested two weeks after salt application (0 mM or 50 mM NaCl) when symptoms of salt stress were observed. Nutrient contents and ratios (K, Ca, Na, K : Na and Ca : Na); superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities malondialdehyde (MDA) chlorophyll a, chlorophyll b, total chlorophyll and carotenoid contents were measured. Mixture modeling and correlation analysis were used in evaluating the experimental data sets. Differences in responses to salt application were observed among genotypes. While all genotypes exhibited negative responses in terms of K : Na ratio, which is an important parameter of salt tolerance, the smallest decreases in K : Na ratios were observed in the YYU-11 (–57.09%) and YYU-4 (–58.78%) genotypes, indicating them to be the most tolerant to salt stress. In general, enzyme activity decreased in response to salt application, although the responses varied among genotypes, especially with regard to CAT and APX activity. The YYU-29 genotype was notable as the genotype with the highest K : Na ratio (1.79) as well as the smallest change in MDA content under salt stress.