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York, United Kingdom

Cook R.T.A.,30 Galtres Avenue | Denton J.O.,Royal Horticultural Societys Garden | Denton G.,Royal Horticultural Societys Garden
Fungal Biology | Year: 2015

The relationship between oak and wisteria powdery mildew, the reason artificial infection of Wisteria sinensis was difficult, and the identity of the pathogen were investigated. Inoculations of detached leaves of Quercus robur with Erysiphe alphitoides from either W. sinensis or Q. robur were successful. Wisteria floribunda was completely and W. sinensis partially resistant. Isolates from wisteria and oak had similar pathogenicities and matching DNA profiles and hence not separable into formae speciales. Instead, oak mildew now includes wisteria and possibly Sorbaria as hosts. On non-host Brassica and cellulose acetate, conidial germ tube development ceased after formation of terminal appressoria. Only Q. robur supported visible lesions. W. sinensis supported fewer colony forming hyphae (CFH) per conidium and smaller hyphal appressoria. Failure to form visible lesions was due to prevention or termination of CFH and not to inhibition of conidial germination or to a host's hypersensitive reaction. Absorption of antifungal compounds via appressoria from maturing host tissue is discussed. The pathogen's DNA ITS region indicated an identification of Erysiphe alphitoides sensu lato, since some isolates did not completely match E. alphitoides sensu stricto. To rapidly indicate susceptibility, a microscopic examination of young leaves 48 h post inoculation is recommended. © 2015 The British Mycological Society. Source


Kiss L.,Hungarian Academy of Sciences | Pintye A.,Hungarian Academy of Sciences | Zseli G.Z.,Hungarian Academy of Sciences | Jankovics T.,Hungarian Academy of Sciences | And 4 more authors.
European Journal of Plant Pathology | Year: 2010

Microcyclic conidiogenesis (MC), a process defined as the production of conidia on a spore without any, or only a minimal, involvement of hyphal growth, has recently been reported in a little known powdery mildew species, Oidium longipes. To investigate whether this was an isolated case or it is a more general phenomenon in powdery mildew fungi, germinating conidia of eight species of the Erysiphales were examined using light microscopy. The following species were included in this work: Erysiphe necator on grapevine, Blumeria graminis f. sp. hordei on barley, Podosphaera xanthii on cucumber, Erysiphe sp. on Ligustrum vulgare, O. longipes on Petunia x grandiflora, O. neolycopersici on tomato, Golovinomyces cichoracearum on Rudbeckia laciniata and Sawadaea sp. on Acer negundo. In all these species, up to 4% of the germinated conidia exhibited MC. Moreover, when colonies of E. necator and O. neolycopersici, on detached grapevine and tomato leaves, respectively, were treated with a conidial suspension of Ampelomyces, the intracellular pycnidia of these mycoparasites appeared in microcyclic conidiophores. This represents a yet undescribed method of accelerating asexual reproduction in this mycoparasite. In the life cycle of powdery mildews, the importance of MC is still not clear but it should be taken into consideration when conidial germination is studied on the host surface for purposes such as epidemiology or species identification. © KNPV 2009. Source


Cook R.T.A.,30 Galtres Avenue | Braun U.,Martin Luther University of Halle Wittenberg | Beales P.A.,Fera
Mycoscience | Year: 2011

Modes of branching of appressoria on conidial germ tubes of 36 Erysiphe spp. were studied. Only unlobed appressoria, termed alobatus pattern, were seen in E. lonicerae, E. magnifica and E. symphoricarpi. Viewed from above with light or scanning electron microscopes, other species had ± irregular lobing, but from below in the plane of contact with the substrate successive dichotomous branchings at 120° were seen to produce a five-lobed appressorium within 6 h. Each division produced a temporarily dormant outward-facing lobe and an inward limb that continued growth and division to form the axis of curved, hooked, single- or double-headed symmetrical or asymmetrical structures in a helicoid cyme-like pattern. Outlines of extracellular material after removal of germinated conidia confirmed this manner of branching. After 36 h some lobes re-divided forming botryose or jigsaw patterns even extending with extra appressoria to form candelabra-like structures. Conidia developed only one true germ tube; rarely secondary unswollen tubes emerged from spare shoulders or ends. The same true germ tubes developed initially on host surfaces, where secondary tubes and/or extensions from appressorial lobes grew into colony-forming hyphae. Lobed appressoria of Neoerysphe and Phyllactinia also branched at 120°. Podosphaera xanthii exhibited a simpler branching pattern. © 2010 The Mycological Society of Japan and Springer. Source

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