Determining the Soilborne Pathogens Associated with Root Rot Disease Complex of Dry Bean in Michigan

Abstract

In Michigan, yield reduction as a result of diminished plant vigor owing to root rot is a major constraint associated with dry bean production and is exacerbated when fields have a history of short crop rotations. Replanting can be necessary when flooding, poor seed germination, or cool soil temperatures result in poor plant establishment, which may be compounded by increased disease pressure. To identify which soilborne pathogens are associated with root rot disease complex on dry bean and to determine their prevalence, a survey was conducted from 2014 to 2018. Dry beans with root rot symptoms were obtained from 39 field locations in 10 counties in Michigan. Rotted roots were washed, potential pathogens were cultured, and isolates were putatively identified into the major pathogen groups based on morphology. Additional identification was conducted with sequencing of the internal transcribed spacer of rDNA for oomycetes and Rhizoctonia and the translation elongation factor 1-α gene for Fusarium isolates. Among the 1,034 isolates obtained, Fusarium (54%) was recovered at the highest prevalence, and oomycetes and Rhizoctonia exhibited a consistent presence, ranging across years from 11 to 30.2% and from 9.3 to 41.8%, respectively. This survey provided baseline information on the prevalence of critical soilborne pathogens of dry bean in Michigan. In the future, additional genetic markers will be utilized to further identify organisms, a species characterization will be conducted to assess pathogenicity and virulence, and dry bean germplasm will be screened for resistance.