First, second, and third authors: Department of Plant Pathology, North Carolina State University, Raleigh 27695.
The evolutionary history of Phytophthora cryptogea and P. drechsleri isolates previously collected from floriculture crops in North Carolina commercial greenhouses was explored with coalescent- and parsimony-based analyses. Initially, 68 isolates representing 13 location–host groups were sequenced at multiple loci. Sequences of all isolates within a group were identical. A subset of isolates were selected, cloned to resolve heterozygous sites, and analyzed with SNAP Workbench. The internal transcribed spacer (ITS) region of the ribosomal DNA and cytochrome oxidase II gene genealogies were congruent and indicated that P. cryptogea and P. drechsleri are sister species diverged from a common ancestor with no evidence of gene flow. In contrast, genealogies inferred from β-tubulin (β-tub) and translation elongation factor 1α (EF-1α) genes were in conflict with these loci. Coalescent analysis based on a nonrecombining partition in β-tub and EF-1α showed an initial (older) split between P. cryptogea and P. drechsleri, with a later (recent) event separating the remaining P. cryptogea haplotypes from P. drechsleri. A parsimony-based minimal ancestral recombination graph inferred recombination between P. cryptogea and P. drechsleri isolates in the ITS region and β-tub, suggesting genetic exchange between species. Also, putative recombination between A1 and A2 mating types of P. cryptogea suggests that sexual reproduction has occurred in the history of these P. cryptogea isolates.