Potential antagonistic fungal species from Ethiopia for biological control of chocolate spot disease of Faba Bean
Chocolate spot disease (Botrytis fabae Sard) is one of most yield limiting constraints of faba bean (Vicia faba). There is promise in using biological control agents to control chocolate spot diseas`es, nevertheless, this strategy has not been fully exploited. The objective of this study was to assess the prevalence of different antagonistic fungi on phyloplane of faba bean in Ethiopia and to evaluate their antagonistic potential against the pathogen. A total of 110 isolates of Trichoderma species were obtained from faba bean leaves from 12 districts, which were grouped into 18 distinct groups differing in colony and other characters. Similarly, 26 distinct isolates belonging to species of Penicillium, Aspergillus, Fusarium and Phioalophora were identified from leaves of faba bean. In vitro and in vivo studies revealed strong antagonistic potential of many isolates. Thirteen isolates of Trichoderma produced 4 mm or more inhibition zone and reduced growth of pathogen colony, when grown in dual culture with it. Antagonistic isolates caused lysis of pathogen mycelium more than 6 mm on agar plates. The antagonists significantly reduced pathogen growth in a range of 24.5 to 0.8 mm. The efficacy of the Trichoderma isolates ranged from 47.6 to 98% and that of the other fungal isolates ranged from 13.1 to 34.5%. On detached leaves, isolates 6-1T, 18-3T and 87T of T. ovalisporum and 52-BT, 108-1T and 108-4T of T. longibrachiatum were found to reduce development of chocolate spot on four genotypes of faba bean. The outcome indicates that biocontrol agents, particularly of species Trichoderma are prevalent on faba bean leaves and can be further explored and developed into effective mycofungicides for management of chocolate spot disease of faba bean.