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

Abstract

During a survey of <i>Phytophthora</i> diversity in natural ecosystems in Taiwan six new species were detected. Multigene phylogeny based on the nuclear ITS, ß-tubulin and <i>HSP90</i> and the mitochondrial <i>cox1</i> and <i>NADH1</i> gene sequences demonstrated that they belong to ITS Clade 7a with <i>P. europaea</i>, <i>P. uniformis</i>, <i>P. rubi</i> and <i>P. cambivora</i> being their closest relatives. All six new species differed from each other and from related species by a unique combination of morphological characters, the breeding system, cardinal temperatures and growth rates. Four homothallic species, <i>P. attenuata</i>, <i>P. flexuosa</i>, <i>P. formosa</i> and <i>P. intricata</i>, were isolated from rhizosphere soil of healthy forests of <i>Fagus hayatae</i>, <i>Quercus glandulifera</i>, <i>Q. tarokoensis</i>, <i>Castanopsis carlesii</i>, <i>Chamaecyparis formosensis</i> and <i>Araucaria cunninghamii</i>. Two heterothallic species, <i>P.</i> x<i>heterohybrida</i> and <i>P.</i> x<i>incrassata</i>, were exclusively detected in three forest streams. All <i>P.</i> x<i>incrassata</i> isolates belonged to the A2 mating type while isolates of <i>P.</i> x<i>heterohybrida</i> represented both mating types with oospore abortion rates according to Mendelian ratios (4-33 %). Multiple heterozygous positions in their ITS, ß-tubulin and <i>HSP90</i> gene sequences indicate that <i>P.</i> x<i>heterohybrida</i>, <i>P.</i> x<i>incrassata</i> and <i>P. cambivora</i> are interspecific hybrids. Consequently, <i>P. cambivora</i> is re-described as <i>P.</i> x<i>cambivora</i> without nomenclatural act. Pathogenicity trials on seedlings of <i>Castanea sativa</i>, <i>Fagus sylvatica</i> and <i>Q. suber</i> indicate that all six new species might pose a potential threat to European forests.