To investigate the effects of exogenous triacontanol （TA） on the growth and physiological characteristics of sainfoin （Onobrychis viciifolia） seedlings under drought stress， three materials （‘Gansu’ sainfoin， new line P1， and 2049） were subjected to -1.0 MPa polyethylene glycol 6000 （T₁） simulated drought stress using a nutrient solution sand culture method. Foliar sprays of TA at 0（CK）， 2.5（T₂）， 5.0（T₃）， 7.5（T₄）， 10.0（T₅）， and 12.5（T₆） μmol·L^-1 were applied， and 21 morphological and physiological indicators were measured to identify the optimal TA concentration. Results demonstrated that all TA concentrations alleviated drought stress， with 10.0 μmol·L^-1 TA （T₅） exhibiting the greatest efficacy. Under T₅ treatment， shoot height， biomass， and photosynthetic parameters increased by 19%-454% compared to T₁， while root-shoot ratio， osmoregulatory substances， and antioxidant enzyme activities decreased by 15%-89%. Principal component analysis identified stomatal conductance， chlorophyll a， and carotenoids as key regulatory indicators. Comprehensive drought resistance evaluation ranked treatments as T₅ > T₆ > T₄ > T₃ > T₂ > T₁， with varietal responsiveness ordered as GS > P1 > 2049. These findings indicated that TA enhanced sainfoin drought resistance by modulating physio-biochemical traits， with 10.0 μmol·L^-1 （T₅） being the optimal treatment， providing a theoretical basis for TA application in drought management during sainfoin cultivation.

Triacontanol  /  Sainfoin  /  Drought Stress  /  Physiological indicators  /  Photosynthetic parameters