Foliar silicon modulates structural and biochemical responses of buckwheat to water deficit

Drought is a major abiotic stressor that limits crop growth and is often associated with oxidative stress. We evaluated whether foliar silicon (Si) application affects primary root anatomy, plant height, and phenolic metabolism in three common buckwheat (Fagopyrum esculentum) cultivars (La Harpe, Panda, and Smuga) exposed to water deficit. Plants were grown under controlled conditions in four treatments: control; drought; control + Si, and drought + Si. Qualitative anatomical assessment revealed that Si promoted more advanced development of the primary root central cylinder, most notably in La Harpe under drought conditions, where a continuous ring of secondary xylem and a well-developed pith were observed. Drought significantly reduced plant height in all cultivars; Si partially alleviated this reduction in La Harpe and Panda, but not in Smuga. Drought generally increased total phenolic content (TPC) and phenolic acid content (PAC) in both leaves and roots, and Si further enhanced these responses, with the highest values under drought + Si. Overall, the results indicate cultivar-dependent effectiveness of foliar silicon (Si) and suggest that Si contributes to coordinated structural and biochemical adjustments under water deficit conditions. To assess the transferability of these responses, further verification across a broader range of genotypes and under different intensities and durations of drought is warranted.