D. Systematics of Oomycota
The phylum Oomycota (Figs.3.7,3.8,3.9,3.10,
3.11,3.12,3.13,3.14, and3.15, Tables3.3,3.4,
and3.5) represents the largest group of osmo-
trophic stramenopiles, with well over 1,000 spe-
cies, encompassing marine, freshwater, and
terrestrial species (Dick2001a,b). They are
ubiquitoussaprotrophsin freshwater and soil
ecosystems (Sparrow 1960 ), and their ecology
and roles have been extensively discussed (e.g.
Dick 1976 , 1990 ,2001a,b; Sparrow 1960 ). Many
oomycetes are opportunistic necrotrophic
pathogens, and others are more specialized
hemibiotrophic and obligate biotrophic
pathogens of plants and animals. Many seem
to be extremely versatile in their ability to
exploit varied niches. For instance,Pythium
insidiosumhas been isolated from both plant
and invertebrate material and is also an oppor-
tunistic pathogen of mammals, including
humans (Mendoza 2009 ). Recent genomic stud-
ies on pathogenic species in genera such as
Aphanomyces (Gaulin et al. 2008 ; Krajaejun
et al. 2011 ),Saprolegnia(Torto-Alalibo et al.
2005 ; Wavra et al. 2012 ), andPythium(Le ́v-
esque et al. 2010 ) have shown they possess a
formidable array ofglucanase- and proteinase-
encoding genes,which have enabled them to so
successfully exploit a wide range of plant and
animal hosts (Jiang and Tyler 2012 ; Jiang et al.
2013 ). Genomic studies have also revealed a
startling array ofpathogenicity factors and effec-
tor molecules, which presumably have enabled
Phytophthoraspecies (Lamour et al. 2007 ; Mor-
gan and Kamoun 2007 ; Qutob et al. 2002 ), downy
mildew species (Baxter et al. 2010 ), and white
blister rusts (Kemen et al. 2011 ; Links et al.
2011 ) to become such successful plant
pathogens.
Sparrow ( 1960 ,1973b, 1976 ) provided the
taxonomic framework for the oomycetes that
was used throughout most of the second half of
the twentieth century (Table3.3). Traditionally,
the oomycetes were divided into four orders:
the Saprolegniales, Peronosporales, Lagen-Table 3.3Taxonomic summary of Oomycota from Sparrow ( 1960 , 1976 )
Saprolegnialean galaxy
Order: Saprolegniales
Family: Saprolegniaceae Achlya,Aphanodictyon,Aphanomyces,Aplanes,Brevilegnia,Calyptralegnia,
Dictyuchus,Geolegnia,Isoachlya,Leptolegnia,Plectospira,Protoachlya,
Pythiopsis,Saprolegnia,Sommerstorffia,Thraustotheca
Family: Leptolegniellaceae Aphanomycopsis,Brevilegniella,Leptolegniella
Family:Ectrogellaceae Ectrogella,Pythiella
Order: Leptomitales
Family: Leptomitaceae Apodachya,Apodachyella,Leptomitus
Order Eurychasmales
Family: Atkinsiellaceae Atkinsiella
Family: Eurychasmaceae Eurychasma,Eurychasmidium
Peronosporalean Galaxy
Order Peronosporales
Family: Peronosporaceae Basidiophora,Bremia,Plasmopara, Peronospora,Peronoplasmopara,
Sclerospora
Family: Albuginaceae Albugo
Family: Pythiaceae Diasporangium,Phytophthora,Pythium,Pythiogeton
Order Lagenidiales
Family: Lagenidiaceae Lagena,Lagenidium,Myzocytium
Family: Olpidiopsidaceae Olpidiopsis,Petersenia,Pseudosphaerita,Rozellopsis
Family: Sirolpidiacae Haliphthoros,Pontisma,Lagenidium,Sirolpidium
Order Rhipidiales
Family:Rhipidiaceae Araiospora,Aqualinderella,Mindeniella,Rhipidium,Sapromyces
Systematics of the Straminipila: Labyrinthulomycota, Hyphochytriomycota, and Oomycota 49