New Disease Reports
New Disease Reports (2006) 13, 3.
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First report of Neoerysiphe galeopsidis on Acanthus spinosus in the UK

R.T.A. Cook 1*, B. Henricot 2 and P. Beales 3

*rtacook@hotmail.com

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Accepted: 10 Feb 2006

In 2005 powdery mildew severely infected Acanthus spinosus, spiny bear's-breech, in the Royal Horticultural Society's Garden (Wisley, Surrey). Initially discrete white patches appeared, mainly on under surfaces of young leaves. By October a dense woolly lawn of conidiophores, bearing very long entangled chains of conidia almost covered these surfaces, the upper surfaces becoming discoloured. Having conidia maturing in chains (Fig. 1) on a herbaceous dicotyledon, the pathogen could be one of three genera. Lobed or kidney-shaped rather than nipple-shaped appressoria on superficial hyphae (Fig. 2) ruled out Golovinomyces (syn. Erysiphe) orontii previously recorded on this host in Britain (Braun, 1995). This, and lack of fibrosin bodies, excluded Podosphaera (syn. Sphaerotheca) and thus suggested Neoerysiphe; this was confirmed by scanning electron microscope images of conidia with structural striations (Fig. 3), leading to longitudinal wrinkling (Fig. 4) typical of the Oidium subgen. Striatoidium anamorph (Cook et al., 1997). Elliptical conidia, 24-43 ´ 13-21.5 µm, and foot cells, 24-50 ´ 7.5-12 µm, straight, cylindrical or often narrowed at the base, fitted N. (syn. Erysiphe) galeopsidis (Braun, 1995).

In the absence of chasmothecia, DNA analysis confirmed the epithet's identity. The ITS region, was amplified using primer sets ITS5/p3 and ITS1/p3, and sequenced as described by Cook et al (in press). The ITS sequence (Genbank DQ350136) was identical to that of N. galeopsidis ex Catalpa spp. (Cook et al., in press) and also to a N. galeopsidis sequence in Genbank (Accession No. AF011300; ex Stachys spp., Lamiaceae).

Braun (1995) confined N. galeopsidis to the Lamiaceae, despite a doubtful record on Geraniaceae, but its host range is clearly broader. Liu et al. (2005) found its chasmothecia on Althaea rosea (Malvaceae) and Cook et al. (1997) reported Oidium spp. with striated conidia on A. mollis (Acanthaceae) and Jaborosa integrifolia (Solanaceae), but without confirming their identity. Recently, Cook et al (in press) confirmed N. galeopsidis on Catalpa spp. (Bignoniaceae). This is its first confirmed record on Acanthus.

Figure1+
Figure 1: Scanning electron microscope image of lawn of conidiophores with catenate conidia. (Bar = 200 µm)
Figure 1: Scanning electron microscope image of lawn of conidiophores with catenate conidia. (Bar = 200 µm)
Figure2+
Figure 2: SEM image of lobed appressoria. (Bar = 20 µm)
Figure 2: SEM image of lobed appressoria. (Bar = 20 µm)
Figure3+
Figure 3: SEM image showing structural striations on penultimate conidium of chain typical of Oidium subgen. Striatoidium anamorph of Neoerysiphe (Bar = 5 µm)
Figure 3: SEM image showing structural striations on penultimate conidium of chain typical of Oidium subgen. Striatoidium anamorph of Neoerysiphe (Bar = 5 µm)
Figure4+
Figure 4: SEM image showing typical longitudinal wrinkling pattern reflecting structural striations (Bar = 10 µm)
Figure 4: SEM image showing typical longitudinal wrinkling pattern reflecting structural striations (Bar = 10 µm)

References

  1. Braun U, 1995. The Powdery Mildews (Erysiphales) of Europe. Jena, Germany: Gustav. Fischer Verlag.
  2. Cook RTA, Inman AJ, Billings C, 1997. Identification of anamorphs of powdery mildews using morphological and host range data. Mycological Research 101: 975-1002.
  3. Cook RTA, Henricot B, Henrici A, Beales P, In Press. Morphological and phylogenetic comparisons amongst powdery mildews on Catalpa in UK. Mycological Research
  4. Liu SY, Takamatsu S, Yang LL, Wang XM, Lu D, Luo L, 2005. First report of Neoerysiphe galeopsidis on Althaea rosea. New Disease Reports [http://www.bspp.org.uk/ndr/] Volume 11.
This report was formally published in Plant Pathology

©2006 The Authors