Mitigating helminthosporium leaf spot disease in sesame: evaluating the efficacy of castor essential oil and sodium bicarbonate on disease management and crop yield enhancement

Helminthosporium leaf spot disease caused by Helminthosporium sesami is one of the most serious foliar diseases of sesame (Sesamum indicum L.), which causes a significant loss in yield and oil percentage. This study aims to investigate the effect of castor (Ricinus communis L.) essential oil and sodium bicarbonate (SBC) on the causal pathogen of leaf spot disease as well as the growth and yield of sesame. A gas chromatography-mass spectrometry (GC-MS) analysis of castor essential oil identified a number of bioactive components. Ricinoleic acid (19.15%) and squalene (9.82%) are two of the most bioactive components in castor oil. In laboratory experiments, castor oil at different concentrations (100, 250, 500, 750 and 1000 µl/L) and SBC at concentrations of 20, 40, 60, 80 and 100 mM were assessed on the mycelium growth of H. sesami. Castor oil at a concentration of 1000 µl/L resulted in the greatest reduction in pathogen mycelial growth (66.67%), while SBC at a concentration of 100 mM gave a high percentage of inhibition (82.96%). Data also show that foliar applications of castor oil and SBC reduced the disease severity of Helminthosporium leaf spot disease of sesame in both greenhouse and field experiments, with SBC being the most effective in reducing the disease severity compared to the control. The agronomic traits of sesame, such as plant height, capsules plant^− 1, weight of 1000 seeds (g), quantity of seeds produced per feddan (kg), and oil % in seeds, were also improved by the treatments.