Powdery mildew taxonomy

The year 2000 saw a major revision of the taxonomy of the powdery mildews originally proposed by Braun (1987). The new monograph saw the recognition of the five major lineages of the Erysiphales therefore establishing the five ‘tribes’ (table 1).

Table 1. Taxonomy of the Erysiphales based on Braun (1999) and Braun and Takamatsu (2000) in comparison with Braun (1987), Braun (1995) (from Braun et al., 2002)

Based on molecular analyses of the gene regions (the ITS region, as well as 18S and 28S rDNA) and superficial analyses of conidial surface patterns, discovered by Cook et al. (1997) under the SEM, these new systematics seem to reflect the diversity of powdery mildews.

Figure 1: Carpinus betulus in the Harris Garden, UoR, with the characteristic white coating of a powdery mildew. The Phyllactinia guttata infecting this common hedgerow plant is partly endoparasitic: producing well-developed superficial hyphae as well as internal hyphae. These develop from hyphae that penetrate through stomata on the leaves’ underside and produce haustoria in mesophyll cells, but do not further elongate into the intercellular spaces. (Photos by Oliver Ellingham)

Importantly, distinguishing characteristics of the Erysiphales seem to comply with this new classification. With all but three of the genera infecting their respective host plants ectoparasitically (fig. 1), those with an endoparasitic (or partially endoparasitic) nature are grouped together within the Phyllactinieae (the Leveillula, Phyllactinia and Pleochaeta).

Figure 1: Types of mycelial parasitism, from left to right showing ectoparasitic, partly endoparasitic and endoparasitic forms of powdery mildew mycelia. (From Takamatsu, 2013)

Figure 2: Molecular phylogenetic tree of the powdery mildews inferred from the combined data set of the 18S, 28S and 5.8S rDNA sequences. White and black branches indicate ectoparasitic and endoparasitic species, respectively. (From Takamatsu, 2013)

Next we will see how other features such as appendage morphology, number of asci per chasmothecium and conidiogenesis type also fit into this updated taxonomy.

References:

BRAUN, U. 1987. A monograph of the Erysiphales powdery mildews.

COOK, R. T. A., INMAN, A. J. & BILLINGS, C. 1997. Identification and classification of powdery mildew anamorphs using light and scanning electron microscopy and host range data. Mycological Research, 101, 975-1002.

TAKAMATSU, S. 2013. Molecular phylogeny reveals phenotypic evolution of powdery mildews (Erysiphales, Ascomycota). Journal of General Plant Pathology (2013): 1-9.