Inhibitory effects of kenaf (Hibiscus cannabinus L.) derivatives on the growth of causal pathogen of leaf blight disease of sunflower (Helianthus annuus L.)

Abstract

Sunflower (Helianthus annuus L.) is an important oilseed crop, but its productivity is significantly constrained by fungal diseases, particularly leaf blight caused by Alternaria spp. This study investigated the isolation, identification, and pathogenicity of fungi associated with leaf blight symptoms in sunflower, and evaluated the inhibitory effects of extracts derived from kenaf (Hibiscus cannabinus L.) biochar, core, and leaf on the growth of the pathogen. Diseased sunflower leaves were collected, surface sterilized, and cultured on Potato Dextrose Agar (PDA) for fungal isolation. The isolates were identified based on cultural and morphological characteristics. Pathogenicity tests were conducted to confirm the causal pathogen of leaf blight disease. The causal pathogen was subjected to molecular evaluation to ascertain its identity. The antifungal activity of kenaf-derived extracts was assessed at 1% and 5% concentrations using the poisoned food technique. Radial mycelial growth of Alternaria tenuissima was measured and compared with an untreated control. Results showed that all extracts significantly (p ≤ 0.01) reduced fungal growth compared to the control. Among the treatments, kenaf core extract at 5% concentration exhibited the highest inhibitory effect having colony diameter of 3.2 mm followed by leaf and biochar extracts, with 3.30 mm and 3.35 mm colony diameter respectively. The findings demonstrate that kenaf-derived materials possess bioactive compounds with antifungal properties capable of suppressing A. tenuissima growth. This suggests their potential as eco-friendly alternatives to synthetic fungicides. Further studies are recommended to isolate and characterize the active compounds and to validate their effectiveness under field conditions.