gate biotrophs(Blair et al. 2008 ; Runge et al.
2011a).
Recently,Phytophthoraclades were reana-
lysed by Runge et al. (2011a) with respect to
their relationship to the downy mildews
(Fig.3.5b; Runge et al.2011a). In their analy-
sis, the monophyletic downy mildew clade
form a sister clade to a group of four species
that included Ph. palmivoraand Ph. mega-
karya, which together were sister toPh. quer-
cina. These in turn form the sister clade to a
group of about a dozen papillate, generally
foliage pathogens, which includePh. infestans
(the type species), Ph. nicotianae, and Ph.
cactorumand which the researchers proposed
as representative of thePhytophthoras. str.
clade(Runge et al. 2011a). Therefore, it is
likely that the genusPhytophthorahas a high
degree of paraphyly with respect to the mono-
phyletic downy mildews. Rather than the
impractical solution of renaming all downy
mildews andPhytophthora spp. asPeronos-
poraspp., because this is the oldest available
genus name for the group, Runge et al. (2011a)
suggest that several new genera should be
described withinPhytophthora to restore the
monophyly of this diverse genus. However, in
a recent phylogenetic analysis based on whole
genomes, albeit of the very restricted number
of five taxa, Seidl et al. ( 2012 ) found that the
downy mildews (represented byHyaloperonos-
pora) were sister to the Phytophthora clade
rather than embedded within it, with the
non-papillate/semi-papillatePh. sojaeandPh.
ramorum species forming a clade that was
sister to the papillateP. infestansas in the
analysis of Runge et al. (2011a).
(vi) Part 3: Downy Mildew Clades
Thedowny mildews(Fig.3.15l–s) are a rapidly
evolving,hyperdiversegroup consisting of 19
genera of obligate biotrophic pathogens of
flowering plants (Table3.5). They typically pro-
duce deciduousconidiosporangiathat are usu-
ally borne on bifurcating persistent aerial
sporangiophores(Fig.3.15k, l, n, o). Downy
mildew oospores are thick-walled, usually
plerotic, and often have verrucose ornamenta-
tion (Fig. 3.15r, s) (Dick 2001a; Sparrow
1973c). They are by far the largest and
most diverse group of oomycetes, estimated to
contain over 800 species, accounting for
more than half of all currently known oomycete
species (Thines and Kamoun 2010 ). As with the
other important plant-pathogenic peronospor-
omycete lineages, the downy mildews have
been extensively sequenced over the past
decade (Garcı ́a-Bla ́zquez et al. 2008 ;Go ̈ker
et al. 2003 , 2004 , 2007 ; Riethmu ̈ller et al. 2002 ;
Runge et al.2011a; Telle and Thines 2012 ; Telle
et al. 2011 ; Thines et al. 2006 , 2007 , 2008 ,2009b;
Voglmayr 2003 ; Voglmayr and Constantinescu
2008 ; Voglmayr et al. 2004 ). An overview of
their taxonomy and phylogeny was recently
given by Thines et al. (2009c). Four major
monophyletic subclades have been recognized
within the downy mildews (Go ̈ker et al. 2007 ;
Thines et al.2009c), which are named on the
basis of morphological characteristics or host
preference (Table3.5).
The earliest diverging group (Thines et al.
2008 ,2009c) in the monophyletic downy mil-
dew clade (Hudspeth et al. 2003 ; Riethmu ̈ller
et al. 2002 ; Thines et al. 2008 ; Telle and Thines
2012 ; Telle et al. 2011 ) seems to be theGDMs
(Fig.3.15k). There is no support for placing
them in their own Sclerosporales order
(Table3.4) introduced by Dick et al. ( 1984 ),
and this order has been rejected in our revised
classification (Table3.5). Among the GDMs are
a monophyletic group of rare monotypic
genera,Graminivora,Poakatesthia, andVien-
notia, all of which have persistent sporangio-
phores (Go ̈ker et al. 2003 ; Thines et al. 2006 ,
2007 ).PoakatesthiaandViennotiaexhibit mor-
phological characteristics that are intermediate
betweenPhytopththoraand the downy mildews
s. str. and have been suggested as being inter-
mediate between the two (Thines 2009 ). Thines
( 2009 ) suggested that the diversification of the
downy mildews might have started from these
Phytophthora-like grass parasites. The second
GDM group has evanescent sporangiophores
and includes the generaEraphthora(Telle and
Thines 2012 ), Peronosclerospora(Fig.3.15k),
Sclerophthora, and Sclerospora (Telle et al.Systematics of the Straminipila: Labyrinthulomycota, Hyphochytriomycota, and Oomycota 75