Investigating the spatiotemporal genetic structure of Phytophthora capsiciin Michigan

Phytophthora capsici isolates were recovered from pepper and cucurbit hosts at seven locations in Michigan from 1998 to 2000. Isolates were characteri zed for compatibility type (CT), mefenoxam sensitivity (MS), and amplified fragment length polymorphism (AFLP) marker profiles. In total, 94 AFLP band s were resolved. Individual populations were highly variable. Within popula tions, 39 to 49% of the AFLP bands were polymorphic and estimated heterozyg osities ranged from 0.16 to 0.19. Of the 646 isolates fingerprinted, 70% (4 54) had unique AFLP profiles. No clones were recovered between years or loc ations. Pairwise F statistics (Phi (ST)) between populations from different locations ranged from 0.18 to 0.40. A tree based on unweighted pair-group method with arithmetic average cluster analysis indicates discrete clusters based on location. Isolates from the same location showed no clustering ba sed on the year of sampling. Analysis of molecular variance partitioned var iability among (40%) and within populations (60%). The overall estimated Ph i (ST) was 0.34 (SD = 0.03). A1/A2 CT ratios were approximate to1:1, and MS frequencies were similar between years for the two locations sampled over time. These data suggest that P. capsici persists in discrete outcrossing p opulations and that gene flow among locations in Michigan is infrequent.