Differential Responses of Onion Genotypes in Plant Growth, Physiological and Biochemical Traits, and Bulb Yield Under Waterlogging Stress

Waterlogging significantly affects plant growth, yield, and quality of due to their shallow roots. We previously identified four waterlogging-tolerant onion genotypes in a pot experiment, which were subsequently evaluated under field conditions along with four sensitive genotypes. This field experiment assessed plant growth, physiological and biochemical traits, and bulb yield under waterlogged conditions with three replications. Accession 1666 exhibited minimal growth reduction, while Bhima Dark Red selection (BDR) selection showed moderate declines of 17.1%, 10.6%, and 11.7% in plant height, leaf number, and total leaf area, respectively, compared to control plots. Both tolerant genotypes maintained higher membrane stability index (MSI), relative water content (RWC), antioxidant enzyme activities, pyruvic acid, and chlorophyll concentrations under stress. Accession 1666 and BDR selection exhibited reductions in bulb yield of 29.7% and 28.8%, respectively, compared to the respective controls. Conversely, sensitive genotypes experienced greater declines in MSI, RWC, and biochemical traits, with total bulb yield reductions ranging from 46.2% (Bhima Raj) to 53.3% (Bhima Shubra). Field performance revealed that Accession 1630 and W-355, previously classified as tolerant, showed higher mortality and lower yields than Accession 1666 and BDR selection. The findings confirmed that Accession 1666 and BDR selection exhibit waterlogging tolerance, making them well-suited for cultivation during the monsoon season. Furthermore, adopting raised bed and furrow planting methods can enhance drainage of excess water, thereby contributing to increased onion yield.