Exogenous abscisic acid mitigates drought stress in pigeon pea by modulating morpho-physiological traits, biochemical responses and gene regulation via ABA dependent and independent pathways

Drought stress is a major constraint to pigeon pea production in rainfed agro-ecosystems. This study evaluates the effectiveness of exogenous abscisic acid (ABA) application in mitigating drought stress through changes in morpho-physiological, biochemical responses, and gene regulation in ABA-dependent and independent pathways in two contrasting pigeon pea varieties PRG 158 and Bahar. An optimal concentration of 100 µM ABA, applied through soil drenching, was identified as effective during the vegetative stage. Physiological and biochemical analyses revealed that ABA pretreatment improved osmotic adjustment and reduced oxidative stress, even under longer duration of water deficit conditions. In PRG 158, exogenous ABA upregulated key drought-responsive genes PYL9 and SnRK2A , indicating a strong ABA-dependent response. Conversely, Bahar exhibited a mixed response, with limited physiological changes despite gene upregulation, suggesting a reliance on ABA-dependent and independent mechanisms. The qRT PCR study also revealed the over expression of drought responsive genes PYL9 and SnRK2A in ABA treated plant as compared to non-treated. Root system architecture and recovery responses also varied between varieties, emphasizing differential adaptation strategies. Overall, the findings demonstrate that exogenous ABA application can modulate drought tolerance in a variety-specific manner by engaging distinct physiological and molecular mechanisms. Soil drenching with 100 µM ABA during early vegetative growth, coupled with minimal irrigation, is proposed as a viable strategy to enhance drought resilience in pigeon pea.