Abstract

Common bean is consumed in large quantities globally but it is highly susceptible to Colletotrichum lindemuthianum, leading to 90 to 100% yield losses. This study investigated the bioactivity of secondary metabolites from Allophylus abyssinicus fungal endophytes against C. lindemuthianum, causing bean anthracnose. A total of 37 fungal endophytes were isolated from the leaves, bark and roots of A. abyssinicus and 20% identified by ITS-rDNA sequence analysis as Aspergillus hancockii, Penicillium christenseniae, Penicillium atrosanguineum and Penicillium manginii. Thirty-three of the endophytes were active against C. lindemuthianum in the dual culture assay with the highest inhibition being 82.6% (A. hancockii). Two of the most active endophytes (A. hancockii and P. christenseniae) were fermented on rice media and their methanol extracts partitioned between ethyl acetate and hexane. Aspergillus hancockii crude hexane extract had the highest inhibition (19.0±1.7mm at 100 mg/ml) against the pathogen under the bioassay screening and 6.3±3.8 mm at 6.25% against C. lindemuthianum under the minimum inhibitory concentration (0.625 mg/ml) screening. Chemical screening of the extracts revealed presence of alkaloids in A. hancockii and P. christenseniae; sterols, triterpenes and coumarins in A. hancockii. These results indicated that fungal endophytes from A. abyssinicus are a source of active compounds that can be used to control C. lindemuthianum affecting common bean.

Key words: Allophylus abyssinicus, Antifungal activity, Colletotrichum lindemuthianum, fungal endophytes, secondary metabolites.