Detection of onion responses to water stress using physiological and biochemical parameters

Onion, an important vegetable crop valued for its culinary and medicinal properties, is highly sensitive to water stress, which significantly affects its growth, yield, and quality. In this study, the response of two onion genotypes to water stress was evaluated using a combination of physiological and biochemical parameters, including thermal imaging. The plants were maintained at five different field capacity levels by gradually achieving the desired stress conditions using a gravimetric approach. The results indicated that water stress caused a marked decline in growth parameters, relative water content, and chlorophyll content, whereas, it induced an increase in malondialdehyde content, proline content and the canopy temperature of leaf tissue in both the genotypes. However, ‘Bhima Shakti’ performed better under water stress than ‘Bhima Shweta’. Drought stress at 60% field capacity caused a significant reduction in relative water content (54.03%), along with increased lipid peroxidation (56.1 nanomoles/g) and a higher canopy temperature (38.0°C) in the susceptible genotype ‘Bhima Shweta’. In contrast, the drought-tolerant genotype ‘Bhima Shakti’ exhibited resilience, maintaining higher relative water content (62.25%), lower lipid peroxidation (42.1 nanomoles/g), and a cooler canopy temperature (36.5°C) under the same level of stress. These findings suggest that relative water content, lipid peroxidation, and canopy temperature could be useful screening tools for assessing water stress tolerance in onion.