Physiological and biochemical determinants of drought tolerance in tetraploid vs diploid sour orange citrus rootstock

Citrus plants face various abiotic stresses like drought during their life span which significantly affect their active growth and development. Tetraploid (4x) plants are more adaptable to environmental constraints than diploid (2x) plants by inducing critical physiological and biochemical processes. In this study, tetraploid and their corresponding diploid sour orange rootstocks were subjected to drought stress for 12 days. Results revealed that drought stress significantly affected plant physiology by reducing photosynthesis rate, stomatal conductance, transpiration rate, and leaf colour, which was prominent in diploid plants compared to tetraploid plants. In diploid plants, phenotypic differences (i.e. wilting and rolling of leaves) were also significant. Diploids with more accumulation of malondialdehyde and hydrogen peroxide in their leaves and roots exhibited more oxidative damage. It was observed that tetraploid plants had higher activities of peroxidase and catalase enzymes, while lower superoxide dismutase was recorded in the leaves and roots of plants. Higher glycine betaine, proline, total soluble protein, total phenolic content, and antioxidant activities were also observed in the leaves and roots of tetraploids. Overall, results suggest that tetraploids in citrus can have better defence mechanisms that help them to sustain under water deficit scenarios.