Six new Phytophthora species from ITS Clade 7a including two sexually functional heterothallic hybrid species detected in natural ecosystems in Taiwan

During a survey of Phytophthora diversity in natural ecosystems in Taiwan a swarm of six new species was detected. Multigene phylogeny demonstrated that they belong to ITS Clade 7a with P. alni, P. cambivora, P. europaea, P. fragariae and P. rubi being their closest relatives. Despite sharing general morphological characters all six new species differed from related species and from each other by a unique combination of characters including the breeding system, oogonial abortion rates, the proportion of ornamented oogonia, ratios of paragynous and amphigynous antheridia, size of sporangia and oogonia, cardinal temperatures and growth rates. Three homothallic species, TW sp.01, TW sp.02 and TW sp. 05, were isolated from rhizosphere soil of Quercus glandulifera, Q. tarokoensis, Castanopsis carlesii, Chamaecyparis formosensis and Araucaria cunninghamii in different forest stands using leaves of Quercus variabilis and Castanopsis indica as baits. The other three species, TWsp.04, TWsp.08 and TWsp.09, which were exclusively detected in three rivers using leaves of Citrus sinensis and Q. variabilis as in-situ baits, were heterothallic. All TWsp.08 and TWsp.09 isolates belonged to the A2 mating type while isolates of TWsp.04 represented both mating types. Abortion rates of oogonia from extensive mating tests were consistently according to Mendelian ratios (4-33%) which was unexpected as the highly polymorphic sequences of the nuclear ß-tubulin, HSP, TRP, ASF and RAS genes demonstrate that two heterothallic species are hybrids. Phylogenetic analyses of ß-tubulin, HSP, TRP, ASF and RAS clones and of cox1 and NADH gene sequences were performed to elucidate the nature of the parental species and clarify whether or not the hybrids might have been involved in the hybridizations that created P. alni ssp. multiformis and P. alni ssp. alni. Pathogenicity trials on Quercus suber seedlings indicate that all six new species might be a potential threat to European forests