Intensity and frequency of abiotic stresses in plants are increasing globally under present changing climatic scenario. The recent decades increasing frequent and severe flooding events due to erratic and unseasonal rainfall pattern negatively impacted the overall agriculture productivity globally. Onion is one of the most water logging sensitive crops as severity of depleting oxygen and light supply to the developing roots are very high, thereby affecting the gas exchange process and inducing anaerobic fermentation pathways ultimately affecting plants normal metabolic pathways in waterlogged soil. Therefore, the present investigation was conducted at ICAR- Directorate of Onion and Garlic Research, Rajgurunagar, Pune, Maharashtra, kharif, 2018-19, to examine the impact of water logging stress in onion. The experiment was conducted in pot condition to provide appropriate artificial water logging condition. The experimental materials comprises of 17 onion entries including red and white onion entries. The seedlings of each entry were raised from seeds in nursery for 45 days with recommended cultural practices and after that transplanted in pot experiment. Thereafter, an artificial water logging condition was imposed to one set for 120 hours and one set was kept as control. Results obtained from experiments indicated that water logging condition significantly affected most of the morpho-physiological parameters in onion genotypes and also it led to enhance defense mechanisms under water logging condition. The percent reduction in leaves and related parameters were recorded lowest in RGP 5 and Acc 1664, whereas it was highest in W 344 and W 448 among the studied onion genotypes under excess moisture condition when compared with control. Though, the percent reduction in survival counts was recorded highest in Bhima Red (99.48) and Bhima Super (99.39), whereas it was lowest in Acc 1630 (80.05) and Bhima Shweta (90.08). Moreover, the percent reduction of recovery was observed highest in Acc 1664 (90.15) and RGP 5 (89.83), whereas it was lowest in W 344 (22.83) and Bhima Dark Red (30.16) among the studied onion genotypes under excess moisture condition when compared with control. The concentrations of antioxidants, secondary metabolites such as phenols and flavonoids which are part of efficient plant defense mechanism, are also found better in RGP 5 and Acc 1664, whereas it was lower in W 344 and W 448 onion genotypes among the studied onion genotypes under excess moisture condition. The percent reduction in single bulb weight was recorded lowest in RGP 5 (1.47) followed by Acc 1664 (19.04) and Bhima Red (21.73), whereas it was highest in W 344 (76.94) followed by W 361 (73.57) and W 448 (65.61) among the studied onion genotypes under excess moisture condition when compared with control. The genotypes which are survived and recovered from the apprehensive stress, it is not necessary that it yields better. The source-sink relationship of individual genotypes defined the ultimate yield potential under various exposures to stress conditions. There is meager work on impact of water logging in onion has been done so far, our study abridge the research gap and strengthening the research material with respect to response of onion under water logging stress.

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