Oomycetes found in wild and cultivated areas of Vietnam

To determine the diversity of oomycetes in Vietnam, particularly in the presumed center of origin of most <i>Phytophthora</i> taxa, isolates were collected from rivers, agricultural soils, and forested areas. Species identification was performed using sequences from the internal transcribed spacer (ITS) and cytochrome 2 oxidase (<i>cox2</i>) regions of the genome. Of the 245 isolates included in this study, the majority (66.5%) were identified as <i>Phytopythium</i> spp., followed by <i>Phytophthora</i> spp. (31%) and <i>Pythium</i> spp. (2.4%). The most prevalent species were <i>Phytopythium vexans</i> and <i>Phytophthora cinnamomi</i>, accounting for 51.8 and 24.5%, respectively, of all isolates obtained. A total of 17 isolates were identified as belonging to multiple undescribed species. From agricultural soils, only one isolate each of <i>Phytophthora</i> and <i>Pythium</i> was obtained, with the remaining 93% belonging to the genus <i>Phytopythium</i>. This study shows that natural and agricultural areas in Vietnam harbor a wide diversity of oomycetes, including several undescribed species. The identification of oomycete species in a center of origin will help identify potential emerging pathogens that can become a threat to U.S. agriculture.