Evening primrose (Oenothera biennis L.) plants under drought stress and jasmonic acid application

Abstract Evening primrose ( Oenothera biennis L.) is a high-value medicinal and oilseed crop whose productivity is increasingly constrained by drought in arid and semi-arid regions. Improving its drought tolerance is therefore of both physiological and agronomic importance. Jasmonic acid (JA) is a key phytohormone involved in stress signaling and antioxidant regulation, yet its role in enhancing drought resilience of O. biennis has not previously been explored. This study aimed to evaluate whether exogenous JA can improve yield, growth, and stress tolerance of evening primrose under water-limited conditions. A bifactorial experiment based on a Randomized Complete Block Design (RCBD) was conducted with three irrigation levels (100, 70, and 40% field capacity, FC) and three JA concentrations (0, 10, and 30 µM), with three replications. Plants were foliar-sprayed with JA three times at two-week intervals. Drought stress substantially reduced biomass production, seed yield, chlorophyll content, stomatal conductance, and relative water content, while stimulating proline accumulation, antioxidant enzymes, phenolic compounds, and membrane damage. Under full irrigation, 30 µM JA significantly increased shoot and root biomass, seed weight, and chlorophyll content. Under moderate and severe drought, JA markedly enhanced root development, improved chlorophyll retention, and strengthened antioxidant defense through higher SOD and CAT activities and greater antioxidant capacity. These physiological adjustments were associated with partial recovery of seed yield under drought with application of 10 or 30 µM JA. Multivariate analyses confirmed that yield and growth traits clustered with well-watered and JA-treated plants, whereas antioxidant and stress markers were dominant under drought. In conclusion, exogenous jasmonic acid improves yield stability of O. biennis by enhancing antioxidant defense, osmotic adjustment, and root growth. JA application represents a practical, low-cost strategy to support evening primrose production under water-limited conditions.