Exploring the genetic diversity of Phytopythium vexans through ISSR markers

Phytopythium vexans is a widespread and harmful species in oomycetes. It infects the roots and crowns of various plants, including crops, ornamentals, and greenhouse products. In recent years phylogenetic analysis of nuclear and mitochondrial gene regions has shown that Pp. vexans has intraspecies diversity and at least three distinct lineages within this species. This study used ISSR markers to analyze the genetic diversity of 118 isolates of Pp. vexans from Australia, Iran, the Czech Republic, and the USA. The Unweighted Pair Group Method with Arithmetic Mean (UPGMA) analysis of ISSR data categorized the isolates into four distinct clusters. Our results suggest a correlation between the cluster grouping and the geographical origin of the isolates. This study shows that the level of gene flow is low among populations. The observed genetic variation in the total isolate collections was 38.8% due to variation between populations. Considering the high genetic diversity among the populations, the low level of gene flow, the high coefficient of genetic diversity, and also based on the PCoA analysis that showed clear boundaries between the four investigated populations, it can be suggested that Pp. vexans is a complex of species and requires taxonomic revision.