Stress physiology of onion genotypes: Insights into waterlogging tolerance and susceptibility

Waterlogging is a major abiotic stress that significantly impairs onion (Allium cepa L.) productivity, particularly during critical growth stages such as seedling establishment, vegetative growth (including leaf and bulb development) and bulbing (bulb formation). This study evaluated the physiological and yield responses of multiple onion genotypes under waterlogging conditions. Various genotypes viz. Bhima Dark Red, Accession 1666, Accession 1630, W-355, Bhima Super, Bhima Shubhra, Bhima Red and Phule Samarth were evaluated. The genotypes Bhima Dark Red, Acc. 1666 demonstrated high tolerance capacity as evident through parameters such as plant height, leaf retention, chlorophyll content, Membrane Stability Index (MSI) and bulb yield under stress. In contrast, cultivars like Bhima Shubhra and Bhima Super, exhibited susceptibility via pronounced reductions in growth and yield parameters. In contrast, susceptible genotypes suffered from oxidative damage, metabolic disruption, showed poor assimilate allocation, resulting in significant yield reduction. The findings highlight the importance of genotype selection and targeted agronomic interventions for mitigating waterlogging-induced yield losses in flood-prone regions. These insights provide a foundation for breeding programs with an aim of enhancing waterlogging tolerance in onion, thereby supporting sustainable production in the context of increasing climate variability.