Aquaperonospora taiwanensis gen. et sp nov in Peronophythoraceae of Peronosporales

Abstract

Twelve isolates of a Pythium-like organism capable of producing Peronospora-like sporangiophores were isolated by baiting from an irrigation ditch in central Taiwan. This organism is described herein as a new genus and species, Aquaperonospora taiwanensis, in Peronophythoraceae of Peronosporales. Low sequence identities in both the ITS and 28S rDNA sequences between A. taiwanensis and representative species of other genera in Peronosporales supported the validity of the establishment of Aquaperonspora as a new genus. The groupings of A. taiwanensis and Pythium ostracodes, and Peronophythora litchii and Phytophthora infestans in both ITS and 28S phytogenetic trees were consistent with the suggestions that Aquasponospora and Peronophythora are transitional genera between Pythium and Peronospora, and Phythophthora and Peronospora, respectively. Based on this study and those reported by others, the determinate growth of sporangiophores is no longer a tenable distinguishing characteristic of Peronosporaceae or Peronophythoraceae. A new key to the families of Peronosporales is, therefore, presented.