Pythiogeton manoomin, a new species causing root and basal stalk rot of wild rice in the United States

Hung K Doan,R Michael Davis

doi:10.1080/21501203.2019.1635216

Abstract

ABSTRACTA new species of Pythiogeton isolated from wild rice exhibiting rot and dieback of roots and stalks in California is described. Pythiogeton manoomin sp. nov. is characterized by coenocytic hyphae, club-like appressorium, and terminal or intercalary sporangia, which are often a short distance from the end of supporting hyphae. The protoplasm is discharged through a discharge tube into an elongate transient vesicle, which soon disappears, leaving the naked protoplasm to differentiate into reniform zoospores. Pythiogeton manoomin also produces thick-walled pigmented chlamydospores, not found in other Pythiogeton species. In greenhouse trials, Pg. manoomin did not infect economically important crops such as rice, bean, chard, corn, carrot, lettuce, oat, radish, sweet pepper, tomato, or wheat. Phylogenetic analysis based on ITS data supports the conclusion that this organism is a new species that is most closely related to Pg. ramosum. In this paper, we describe morphological characteristics, temperature–growth relationships, pathogenicity, and phylogenetic relationships that support the description of this taxon as a new species, Pythiogeton manoomin sp. nov.urn:lsid:zoobank.org:pub:4C63AAA4-4D4A-4679-A344-79B75121A5C6

Highlights

The genus Pythiogeton (Pg.), together with Pythium and Phytophthora, belongs to the family Pythiaceae of the Oomycota
We describe morphological characteristics, temperature–growth relationships, pathogenicity, and phylogenetic relationships that support the description of this taxon as a new species, Pythiogeton manoomin sp. nov
Pythiogeton species are characterized by production of zoospores outside of sporangia from a naked mass of protoplasm, not from a vesicle, which is characteristic of Pythium species

Summary

Introduction

The genus Pythiogeton (Pg.), together with Pythium and Phytophthora, belongs to the family Pythiaceae of the Oomycota. The Pythiogeton genus encompasses 15 recognized species: Pythiogeton utriforme (Minden 1916), Pg. ramosum (Minden 1916), Pg. transversum (Minden 1916), Pg. autossytum (Drechsler 1932), Pg. uniforme (Lund 1934), Pg. dichotomum (Ito and Tokunaga 1935), Pg. nigrescens (Batko 1971), Pg. zeae (Jee et al 2000), Pg. zizaniae (Ann et al 2006), Pg. abundans (Huang et al 2012), Pg. microzoosporum (Huang et al 2012), Pg. oblongilobum (Huang et al 2012), Pg. paucisporum (Huang et al 2012), Pg. proliferatum (Huang et al 2012), and Pg. puliensis (Huang et al 2012). Most described Pythiogeton species are saprophytic, with only three species, Pg. zeae, Pg. zizaniae, and Pg. ramosum known to be pathogenic to corn, water bamboo, and ginger, respectively (Jee et al 2000; Ann et al 2006; Le et al 2014)

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