Pythium, Pythiogeton and prov. name Phytopythium: The current status for the species in the genera

Traditionally, genera and species in Oomycetes have been distinguished and defined based on morphological characteristics. The genus Pythium is characterized by its well developed hyaline mycelial thallus and the way zoospores are developed and discharged: the sporangium forms a discharge tube throu...

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Bibliographic Details
Published in:Phytopathology 2010-06, Vol.100 (6), p.S150-S150
Main Authors: De Cock, AW, Robideau, G P, Bala, K, Coffey, MD, Abad, Z G, Levesque, CA
Format: Article
Language:English
Subjects:
Lagenidium
Oomycetes
Phytophthora
Pythium
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Summary:Traditionally, genera and species in Oomycetes have been distinguished and defined based on morphological characteristics. The genus Pythium is characterized by its well developed hyaline mycelial thallus and the way zoospores are developed and discharged: the sporangium forms a discharge tube through which the contents move out and form a vesicle at the tip with an undifferentiated mass of protoplasm. This mass then differentiates into biflagellate zoospores. Although this way of zoospore discharge is shared by all Pythium species, the genus is heterogeneous with regard to morphological characters like e.g. the sporangium shape. The genera Pythiogeton and Lagenidium display a way of zoospore discharge similar to that in Pythium, though they are considered different genera based on other characteristics. DNA sequence analyses allow an evaluation of the morphological classification over a phylogenetic framework. Analysis of ribosomal DNA regions and the mitochondrial COI showed that a clade within Pythium is actually more closely related to Phytophthora than to Pythium; this clade is provisionally named Phytopythium. Moreover, molecular analyses revealed the close relationship of Pythiogeton and some Lagenidium species to Pythium. The phylogenetic results will be discussed with regard to morphology.
ISSN:0031-949X