Unraveling drought tolerance in spray chrysanthemum through multivariate analysis under hydroponic and pot culture conditions

Drought affects chrysanthemum growth and yield, highlighting the need for reliable indicators of tolerance. This study evaluated 68 genetically diverse genotypes under hydroponics and pot culture using a completely randomized design to identify key physiological, biochemical and morphological traits linked to drought adaptation. Stress was imposed with 10 % polyethylene glycol (PEG) in hydroponics at the seedling stage and 60 kPa soil moisture tension in pots for 10 days at the vegetative stage based on our preliminary studies. Traits measured included chlorophyll content, carotenoids, relative water content (RWC), membrane stability index (MSI), canopy temperature depression (CTD), chlorophyll fluorescence, biomass and reproductive parameters. Correlation analysis revealed strong positive associations among chlorophyll content, RWC, MSI, CTD and fluorescence, suggesting coordinated mechanisms that preserve photosynthetic efficiency and cellular stability. Principal component analysis (PCA) identified chlorophyll b, fluorescence, biomass and reproductive traits as major contributors to phenotypic variation. The first few PCs explained 71.0 % variation in hydroponic control, 75.5 % in hydroponic stress, 61.6 % in pot control and 77.9 % in pot stress, indicating context-dependent adaptive strategies. Under hydroponic stress, chlorophyll a, total chlorophyll, biomass, chlorophyll b and carotenoids contributed strongly to both PC1 and PC2, with Punjab Singar, Violet, Gulmohar, Garden Beauty and Shwet excelling in these traits, while Autumn Joy and Naughty White were distinguished by flowers per plant and chlorophyll a/b. In contrast, under pot stress, no trait contributed simultaneously to both PCs. Overall, chlorophyll content, RWC, MSI, CTD, chlorophyll fluorescence and reproductive traits emerged as robust indicators for breeding drought-resilient chrysanthemum cultivars.