Identification of cold tolerant French marigold genotypes using morpho-biochemical parameters

French marigold (Tagetes patula L.) is a widely cultivated ornamental species, valued for its vibrant blooms and adaptability. However, low winter temperatures in northern India can adversely impact its vegetative growth and floral development, particularly during the early growth stages that coincide with peak winter. To assess cold stress tolerance, twenty French marigold genotypes were evaluated under natural winter conditions (November 2022–February 2023) in New Delhi. Various morphological traits (plant height, leaf length, and width), floral traits (days to visible flower bud colour, number of petals, petal dimensions, flower longevity), and biochemical parameters (chlorophyll a and b content) were studied. A significant genotypic variability was observed across all traits. Gulzafri Yellow (GY) and Gulzafri Orange (GO) recorded maximum plant heights (25.86 cm and 23.76 cm at 50 DAT, respectively), while ‘IIHR-MO-4’ showed the largest leaves (14.66 cm and 7.70 cm in length and width respectively). ‘Fr. /R-5’ exhibited the highest petal count (180.58), chlorophyll a content (9.78 mg g⁻¹ FW), and longest flower longevity (17.81 days). Principal Component Analysis (PCA) revealed that leaf size, plant height, petal number, and chlorophyll a were key contributors to cold tolerance, explaining 74.18% of the total variation. Correlation analysis confirmed strong associations between vegetative vigour, chlorophyll retention, and floral traits. The study involved meticulous evaluation during the winter season to accurately record genotypic responses to cold stress under natural conditions, leading to the identification of promising cold-tolerant French marigold genotypes. It established a robust morpho-biochemical framework for genotype selection, highlighting that a combination of morphological, floral, and biochemical traits can serve as reliable indicators for screening cold-tolerant lines. Notably, ‘Gulzafri Yellow’ (GY), ‘Gulzafri Orange’ (GO), ‘IIHR-MO-4’, and ‘Fr./R-5’ emerged as potential candidates for winter breeding programs.