Taxonomic Review of the Genus Pythium (Oomycota), with Description of New Species

Taxonomic Review of the Genus Pythium (Oomycota), with Description of New Species

Bora Nam and Young-Joon Choi*

Department of Biological Science, Kunsan National University, Gunsan 54150, South Korea

Center for Convergent Agrobioengineering, Kunsan National University, Gunsan 54150, South Korea

*Email: yjchoi@kunsan.ac.kr

Recent phylogenetic studies suggested splitting up the genus of Pythium Pringsheim (nom. cons.) sensu lato (s.l.) into five distinct genera, namely Elongisporangium, Globisporangium, Phytopythium (= Ovatisporangium), Pilasporangium, and Pythium sensu stricto (s.s.). The division of Pythium s.l. was validated by cox1 phylogenetic tree, in which clades A–D of Pythium s.l. have merged into Pythium s.s. Members of this group are characterized by filamentous sporangia and are often associated with aquatic habitats. During an oomycetes survey from 2016 to 2021 in Korea, numerous isolates of Pythium s.s. were found in aquatic ecosystems, with the highest abundance and species diversity, among different oomycete genera. Morphological, physiological, and phylogenetic analyses of ITS, cox1, and cox2 datasets allowed to distinguish a total of ten taxa of Pythium s.s. as previously unrecorded in Korea and six novel taxa. In the present study, these taxa were described using morphological and phylogenetic data, and compared with already known species of Pythium s.s. Moreover, we characterized the congeners of Pythium s.s. by differentiating them based on morphology, phylogeny, and ecology from the new genera split from Pythium s.l. Our findings contribute valuable information, expanding the current understanding of the taxonomy of Pythium s.s. and establishing a fundamental information for future research.