Pathology of oak-wisteria powdery mildew.

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.

Phytophthora niederhauserii sp. nov., a polyphagous species associated with ornamentals, fruit trees and native plants in 13 countries.

A non-papillate, heterothallic Phytophthora species first isolated in 2001 and subsequently from symptomatic roots, crowns and stems of 33 plant species in 25 unrelated botanical families from 13 countries is formally described here as a new species. Symptoms on various hosts included crown and stem rot, chlorosis, wilting, leaf blight, cankers and gumming. This species was isolated from Australia, Hungary, Israel, Italy, Japan, the Netherlands, Norway, South Africa, Spain, Taiwan, Turkey, the United Kingdom and United States in association with shrubs and herbaceous ornamentals grown mainly in greenhouses. The most prevalent hosts are English ivy (Hedera helix) and Cistus (Cistus salvifolius). The association of the species with acorn banksia (Banksia prionotes) plants in natural ecosystems in Australia, in affected vineyards (Vitis vinifera) in South Africa and almond (Prunus dulcis) trees in Spain and Turkey in addition to infection of shrubs and herbaceous ornamentals in a broad range of unrelated families are a sign of a wide ecological adaptation of the species and its potential threat to agricultural and natural ecosystems. The morphology of the persistent non-papillate ellipsoid sporangia, unique toruloid lobate hyphal swellings and amphigynous antheridia does not match any of the described species. Phylogenetic analysis based on sequences of the ITS rDNA, EF-1α, and ß-tub supported that this organism is a hitherto unknown species. It is closely related to species in ITS clade 7b with the most closely related species being P. sojae. The name Phytophthora niederhauserii has been used in previous studies without the formal description of the holotype. This name is validated in this manuscript with the formal description of Phytophthora niederhauserii Z.G. Abad et J.A. Abad, sp. nov. The name is coined to honor Dr John S. Niederhauser, a notable plant pathologist and the 1990 World Food Prize laureate.