Distribution and characterization of fusarium species causing common bean root rot in Uganda
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Fusarium root rot of common bean is an economically important disease in Central America, South America and Africa. Yield losses due to Fusarium root rot of common beans can reach up to 86%. A disease survey was conducted in six agroecologies of Uganda to determine the incidence and prevalence of Fusarium root rot of common beans in Uganda. Some of the samples from each field were collected for pathogen isolation to conduct morphological, pathogenic and molecular characterization using PCR amplification of Inter Simple Sequence Repeat markers and PCR amplification and sequencing of Translation Elongation factor alpha gene region. The incidence and prevalence of root rot varied across agroecologies. The highest prevalence and incidence were observed in the Karamoja Pastoral zone and lowest values were observed in the West Nile Farming system zone. The isolates differed in colony color, growth rate and shape of microscopic structures. Four pathogenicity experiments were conducted and all isolates evaluated were pathogenic on common bean and caused root rot and wilting of seedlings. PCR amplification of Inter Simple Sequence Repeats produced a phylogenetic tree in which the isolates formed nine clusters. BLASTn following sequencing of Translation Elongation factor 1 alpha (TEF 1 α) gene region of the isolates yielded closest relationships with Fusarium species such as F. solani, F. falciforme, F. incarnatum, F. brachygibbosum, F. duofalcatisporum, F. equiseti, F. Delphinoides, F. fredkrugeri, Fusarium strain 15 Ar047 and Fusarium oxysporum. Fusarium species causing common bean root rot in Uganda are diverse and all the market varieties encountered during the surveys were susceptible to the disease. Yield losses due to Fusarium root rot need to be studied so that more breeding efforts are directed towards identifying and incorporating Fusarium root rot and wilt resistance in popular bean varieties.