Evaluation of the effectiveness of turmeric and ginger in inhibiting the growth of the fungus, Aspergillus niger, the causal agent of black mold disease of onion

Abstract

Black mold, predominantly caused by Aspergillus niger, is a major postharvest constraint affecting onion bulb quality and storage life. The increasing need for safer alternatives to conventional fungicides has stimulated interest in plant-derived antifungal treatments. This study investigated the fungal etiology of black mold in onion bulbs and evaluated the efficacy of turmeric and ginger powders and extracts against A. niger under laboratory and storage conditions. Among the fungi isolated from diseased bulbs, A. niger was predominant (80.0%), followed by Penicillium spp. (13.3%) and Botrytis spp. (6.6%). All 12 A. niger isolates exhibited pathogenicity, with disease severity ranging from low to 80.0%; isolate No. 2 was the most virulent. In vitro assays demonstrated concentration-dependent antifungal activity of both botanical treatments. At 3%, turmeric and ginger powders produced the highest growth inhibition (79.1%), while their extracts achieved 75.0% inhibition, compared with no inhibition in the untreated control. Under storage conditions, all treatments markedly suppressed disease development relative to the untreated control, which recorded 95.48% disease severity. Ginger powder provided the greatest protection, reducing disease severity to 22.30%, followed by turmeric extract (22.90%) and turmeric powder (32.70%). These findings highlight the strong antifungal potential of readily available turmeric and ginger preparations, particularly ginger powder, for suppressing A. niger and extending the storage quality of onion bulbs. Their practical potential warrants further validation under commercial storage conditions, including optimization of dosage, application method, and treatment timing.