The purpose of this study was to identify the primary pathogen(s) associated with root/crown rot (RCR) in dry bean samples collected at breeder nursery sites and farmer fields in Mozambique using molecular sequencing and culture-based methods.
Dry edible beans are a vital food source in Mozambique, East Africa—one that alleviates hunger and malnutrition and adds value to the economy. In recent years, root/crown rot (RCR) pathogens have emerged as limiting constraints in dry bean production. Not much has been characterized concerning the causal agents of RCR in Mozambique. In the current study, sequencing revealed, not surprisingly, an increased diversity of fungal/oomycete operational taxonomic units when compared to culture-based methods oof diversity. Species of Fusarium, mainly F. oxysporum, were the dominant taxa detected in RCR dry beans through sequencing the ITS rDNA region and partial EF-1α gene. Collectively, 333 fungi and/or Oomycetes were isolated in culture during the 2014–2015 growing seasons and tested for pathogenicity on healthy bean seedlings. Fusarium species were identified by both morphological and molecular characters. At least 60 percent of the isolates inoculated on common bean were recognized as potentially pathogenic. From both isolation frequency and pathogenicity testing, F. oxysporum and related species play an important role in the bean RCR complex. Similar results were found from dry beans grown in the two main bean-growing regions of Mozambique. These findings will enable breeders to screen for resistance to F. oxysporum in greenhouse-grown bean plants, as well as within field-grown bean cultivars. (publisher abstract modified)