APS Abstracts of Presentations

Identification and characterization of Phytophthora capsici on bean in Michigan
A. J. GEVENS (1), R. S. Donahoo (2), K. H. Lamour (2), M. K. Hausbeck (1)
(1) Michigan State University, East Lansing, MI 48824, USA; (2) University of Tennessee, Knoxville, TN 37996, USA
Phytopathology 96:S39

Commercial snap and wax bean fields exhibited water-soaked foliage, stem necrosis, and plant decline along the surface water drainage pattern in Oceana, Cass, and Van Buren counties, Michigan. All fields have a history of Phytophthora capsici infestation and were sampled in 2003 to 2005. Diseased tissue from stems, petioles, leaves, and pods yielded 680 P. capsici isolates. No isolates were recovered from roots. Koch’s Postulates confirmed P. capsici as the pathogen. Representative isolates were also pathogenic on cucumber fruit. Most isolates (75%) were intermediately or fully sensitive to the fungicide mefenoxam and more than half were of the A1 compatibility type. Under laboratory conditions, 6 select isolates were all pathogenic on 12 bean types, including soybean, causing water-soaked lesions, necrosis, and wilting. Isolates (131) from 2003 and 2004 were subjected to amplified fragment length polymorphism analysis to investigate genetic diversity among bean and cucurbit isolates, bean tissues, and among geographical locations. Results indicated that there is no pathogen population subdivision based on host or bean tissue. Isolates exhibited similarity based on geographical location. This is the first documentation of P. capsici on snap and wax beans in Michigan.

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