Phytophthora asiatica sp nov., a new species causing leaf and stem blight of kudzu in Japan

A slow growing, nonpapillate, homothallic Phytophthora species was isolated from leaf and stem blights of kudzu (Pueraria lobata) in the Toyama and Ishikawa districts of Japan. The isolates could not be assigned to an existing taxon and were characterized in a morphological study and a phylogenetic analysis. They were found to differ from related Phytophthora species by their characteristic obturbinate, often distorted sporangia with external proliferation, moderately large oogonia with aplerotic oospores, predominantly amphigynous but occasionally paragynous and intercalary antheridia, the presence of catenulate hyphal swellings, their high optimum temperatures for growth, and their relatively slow radial growth rates. An unusual characteristic was the germination of zoospores within the sporangia. In the phylogenetic analyses involving sequences from seven nuclear and two mitochondrial genes, the isolates formed a distinct monophyletic group within Phytophthora clade 7 with strong bootstrap support. On the basis of their unique combination of characters, the isolates are considered to be a new species and are formally described as Phytophthora asiatica sp. nov.