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Screening extracts of bacterial endophytes isolated from Allophylus abyssinicus (Hochst. Radlk.) for control of bean anthracnose

¹Center for International Forestry Research and World Agroforestry (CIFOR-ICRAF), Trees Theme, Kenya
²Egerton University, Biological Sciences, Kenya
³Egerton University, Dept. of Chemistry, Kenya

Abstract

Common beans are among the major crops cultivated and consumed in large quantities worldwide due to their high protein and fiber contents. However, it is prone to fungal attacks majorly by Colletotrichum lindemuthianum causing anthracnose, leading to 90-100% yield losses. This study investigated the bioactivity of secondary metabolites of bacterial endophytes isolated from Allophylus abyssinicus against C. lindemuthianum in vitro. The endophytes were isolated from sterilized leaves, bark and roots of A. abyssinicus and cultured on nutrient agar. A total of 15 bacterial endophytes were isolated and one of the most active bacterial endophytes was identified. Most of the bacterial endophytes were active against C. lindemuthianum with the highest inhibition being 72.5% Lysinibacillus fusiformis, in the dual culture assay. Lysinibacillus fusiformis was fermented in nutrient broth and extracted using ethyl acetate and hexane to yield hexane and ethyl acetate extracts. Disc diffusion method was used to determine the antimicrobial activities (bioassay) of the extracts against C. lindemuthianum. The crude ethyl acetate extract from the Lysinibacillus fusiformis (100 mg/ml) had the highest inhibition 32.7±6.5 mm against the pathogen compared to hexane extract with an average inhibition of 22.3±5.7 mm. Minimum inhibitory concentration (MIC) was determined for all the active extracts against C. lindemuthianum and ethyl acetate extracts of Lysinibacillus fusiformis had the lowest MIC of 0.078 mg/ml. Various chemical constituents were detected in A. abyssinicus bacterial endophytes extracts including saponins, flavonoids, alkaloids and coumarins. These results show that bacterial endophytes isolated from A. abyssinicus are a source of compounds that can be used in the control of C. lindemuthianum affecting common bean in Kenya.

Keywords: Allophylus abyssinicus, Antifungal activity, bacterial endophytes, Colletotrichum lindemuthianum, secondary metabolites

Contact Address: Hellen Kariuki, Center for International Forestry Research and World Agroforestry (CIFOR-ICRAF), Trees Theme, 529-20107 njoro nakuru kenya, Nairobi, Kenya, e-mail: hgathiru2gmail.com