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Abstract

This study aimed to evaluate the effects of drought stress and salicylic acid (SA) on the growth parameters and secondary metabolites of Rhaponticoides schmidii Wagenitz, a critically endangered medicinal species. The treatments consisted of three irrigation regimes (control: 80% field capacity; moderate stress: 60% FC; and severe stress: 40% FC) combined with three SA concentrations (0, 0.05, and 1 mM). The results revealed that both drought and SA treatments, and their interaction, significantly affected physiological, biochemical, phenological, and yield-related traits. Severe drought stress (40% FC) decreased chlorophyll a, chlorophyll b, total chlorophyll content, and soluble protein by 51, 33, 46, and 28%, respectively, and shortened phenological stages by about eight days. Yield components, including the number of cypselae/plant, percentage of healthy seeds/plant, seed weight, and total number of seeds/plant by 44%, 43%, 35% and 32%, respectively, compared with the control. In particular, the treatment with 1 mM SA significantly enhanced the activities of ascorbate peroxidase (APX) and peroxidase (POD), as well as DPPH radical scavenging capacity, by 31%, 21%, and 52%, respectively, in plants under severe drought stress. This treatment also produced the highest levels of flavonoids (Scutellarin, Visinin, Rutin, Quercetin, Kaempferol, Apigenin, and Luteolin) and phenolic compounds, while the lowest values occurred under well-watered (80% FC) conditions without SA. Overall, salicylic acid effectively mitigated the adverse impacts of drought stress, enhanced antioxidant activity, secondary metabolite accumulation, and yield potential in the critically endangered plant, Rhaponticoides schmidii Wagenitz

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