Strigolactone and Abscisic Acid Positively Regulate Morphophysiological Traits and Gene Expression in Locally Grown Sorghum bicolor L under Drought Conditions

Drought stress markedly constrains plant growth and productivity by disrupting physiological and biochemical homeostasis.Sorghum bicolor L., a drought-tolerant C4 crop, is an appropriate model for investigating hormone-mediated stress responses.This study evaluated the morphological, physiological, biochemical, and gene expression responses of local S. bicolor genotypes under polyethylene glycol (PEG)-induced drought stress, combined with exogenous abscisic acid (ABA) and strigolactone (SL) treatments, including a post-stress recovery phase.PEG stress significantly reduced shoot and root length and root number (up to 48%), particularly in plants without hormonal application.In contrast, SL substantially improved shoot and root growth during both stress and recovery.The chlorophyll ratio decreased by 72% under PEG stress but was restored by SL and ABA+SL treatments, indicating improved photosynthetic resilience.PEG stress increased proline (45%), malondialdehyde (MDA; 55%), and hydrogen peroxide (HO; 10%) levels, consistent with drought stress and oxidative damage.Exogenous ABA and SL reduced lipid peroxidation and reactive oxygen species (ROS) accumulation, with SL showing greater efficacy in the local S. bicolor genotypes.Antioxidant enzyme activities (CAT, POD, and APX) increased under stress, with relatively higher activities observed under ABA treatment.Gene expression analyses revealed differential regulation of SbCAT, SbAPX, and SbSLAC1.Both ABA and SL strongly induced SbCAT and SbAPX, whereas SbSLAC1 was primarily upregulated under PEG stress combined with ABA.Overall, ABA and SL enhance drought tolerance in sorghum through coordinated activation of antioxidant defenses, drought adjustment, and stress-responsive gene expression, with SL playing a prominent role in promoting morphological recovery and maintaining redox balance during post-stress adaptation.