Identification of Elsinoë phaseoli causing bean scab in Kenya and evaluation of sporulation using five adapted techniques

Abstract

This research addresses the presence of Elsinoë phaseoli in Kenya, where information on the biology of this pathogen remains scarce. Employing a multifaceted approach, the study demonstrates the steps taken to isolate, identify, and characterize E. phaseoli as the pathogen responsible for scab on common bean. Field observations confirmed scab symptoms, particularly the prominent pod lesions. Elsinoë phaseoli was isolated from common bean using a targeted streaking method on older acervulus-bearing lesions. Morphological examinations revealed a notable diversity within E. phaseoli colonies, consistent with the characteristics of the genus. Molecular identification through ITS-rDNA sequencing confirmed isolate AscoSK1 obtained in this study as belonging to E. phaseoli, offering a robust species differentiation method. Assessing conidium production required the implementation of five different culture methods. An adaptation of the Scheper et al. (2013) method yielded the highest quantity of conidia from 25 colonies spaced at 1 cm apart, with a conidial yield of 5.0 × 10⁶ conidia per 9-cm-diameter Petri dish. A higher conidial yield was attained after the colonies were pre-incubated on potato dextrose agar in the dark at room temperature for 28 days, followed by a transfer to corn meal agar for an additional 2 days at 20°C. This emphasizes the pivotal influence of incubation duration and pre-culture conditions on the process. This research provides insights into the biology of E. phaseoli and introduces an improved method for enhancing in vitro sporulation of the pathogen, setting groundwork for future research and handling.