Physiological, Biochemical, and Molecular Responses of Potato Cultivars to Osmotic Stress Under In Vitro Shoot Culture

Drought is a major limiting factor for potato productivity. This study examined two Kazakh potato cultivars, Tokhtar and Aksor, under osmotic stress induced by polyethylene glycol (PEG)-6000 using an integrated physiological, biochemical, and molecular approach. We evaluated plant growth, total chlorophyll content, catalase activity, malondialdehyde content, and the transcript levels of six stress-associated genes (StMYB306-like, StuNAC, TRE, OST2, and EPF1, and EPF2) across increasing PEG concentrations. PEG treatment significantly inhibited growth and reduced total chlorophyll content while increasing CAT activity and MDA accumulation. The magnitude and statistical significance of the morphological and biochemical responses varied between cultivars and among PEG concentrations. Transcript levels of StMYB306-like, StuNAC, TRE, and OST2 generally increased with increasing PEG concentration, while EPF1 and EPF2 levels decreased. The absence of significant cultivar × PEG interactions for all six genes indicated that their transcriptional responses to PEG did not differ statistically between Tokhtar and Aksor. Correlation and multivariate analysis revealed contrasting associations between growth and chlorophyll-related traits and CAT activity, MDA accumulation, and stress-responsive gene expression. To our knowledge, the expression patterns of TRE, OST2, and EPF1 and EPF2 in potatoes under PEG-induced osmotic stress have not been characterized previously. Taken together, these findings characterize the coordinated morphological, biochemical, and transcriptional responses of potato plantlets to PEG-induced osmotic stress. They also identify candidate response traits for validation across genetically diverse germplasm and under soil-based and field drought conditions.