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Is phytophthora infestans a good taxonomist? host recognition and co-evolution in the Phytophthora/Solanum interaction

Abstract:

The oomycete plant pathogen Phytophthora infestans has been isolated from wild and cultivated Solanum hosts in the highlands of Ecuador. Previous studies identified four general groups of pathogens based on several genetic and phenotypic markers. With only a few exceptions, each pathogen group was primarily associated with one host species, or one group of closely related host species. The current study was designed to test the hypothesis that comparison of host and pathogen phylogenies would indicate co-evolutionary processes. A phylogeny of 200 pathogen isolates was derived from 12 simple sequence repeat (SSR) markers. This was compared with a published phylogeny of the host genus Solanum. Based on SSR data, pathogen isolates clustered into two major clades, one associated uniquely with four host sections and the other uniquely with three sections. Isolates from both of the major clades were associated with the host section Lasiocarpa. Overall, the two phylogenies were congruent, and the congruency between them appeared consistent with a model of host tracking co-evolution, with several exceptional cases that could be explained by host jumping.