Virulence, inulinolytic potency and biological control of fungi associated with banana leaf blight disease

Abstract

A leaf blight disease is the widespread infection of bananas in tropical and subtropical regions. Early symptoms included irregular, tiny, necrotic lesions ranging in colour from pale grey to black-brown, mainly affecting the top three to five leaves. Necrotic and withering leaves indicated severe infection. Thirty-one fungal isolates were isolated from 30 samples of symptomatic banana leaves, collected from the field, on Potato Dextrose Agar (PDA) medium. The initial morphological identification of the isolates was confirmed using a molecular technique that involved amplifying the genes of β-tubulin for all collected isolates and cytochrome b for AspergillusNigri group. The pathogenicity test and re-isolation of the pathogen were done to confirm Koch's postulates. Light microscope and scanning electron microscopy were applied to notice the mycological infections in tested banana leaves. All collected isolates were evaluated to inulinase activity. Phytopathogenic fungi were biologically controlled by using four antagonistic fungal strains, Aspergillus flavipes, Phoma sp., Epicoccumpurpurascens and Verticilliumalbo-atrum. The results indicated that eighteen species represented by thirty-one isolates were recorded by phylogenetic analysis. Achroiostachys levigata (AEMC2 and 3) and Colletotrichum musae (AEMC16) exhibited pathogenic activity with highly virulent range (+++) and produced leaf lesions with 15–18.66 mm. Eighteen strains of banana leaf blight fungi were inulinase producers with variable proficiencies. The highest activity, 148.02667 U/ml was verified by Epicoccum nigrum (AEMC20). Phytopathogenic fungal growth was significantly suppressed by Epicoccum purpurascens and Aspergillus flavipes with maximum repression percentage of 50%. Therefore, biological control can be used to reduce the usage of chemical fungicides against leaf blight disease-caused fungi.