Comparison of ITS sequences from UK and North American sugar-beet powdery mildews and the designation of Erysiphe betae

New Records of Powdery Mildews from Taiwan: Erysiphe ipomoeae comb. nov., E. aff. betae on Buckwheat, and E. neolycopersici comb. nov. on Cardiospermum halicacabum

Erysiphe is the largest genus of powdery mildews (PMs), a group of obligate plant pathogenic fungi. Exploration of biodiversity generally relies on regional surveys and our aim is to investigate the PMs in Taiwan. Collections of the fungi on five plant species around agricultural environments were subjected to morphological and molecular characterization, using both internal transcribed spacer (ITS) and β-tubulin gene (TUB2) regions for the phylogenetic analyses. Erysipheipomoeae comb. nov., a species able to infect Ipomoea obscura and I. aquatica demonstrated by pathogenicity tests, has been neotypified. The two buckwheat species, Fagopyrum esculentum and F. tataricum, are found to be hosts of E. aff. betae. These results suggest that hosts in some plant families can be infected by more than one Erysiphe pathogen, e.g., Convolvulaceae by E. ipomoeae and E. convolvuli and Polygonaceae by E. polygoni and E. aff. betae, respectively. In addition, phylogenetic analyses of PMs on Cardiospermum halicacabum and tomato belonging to the E. aquilegiae complex are allocated under E. neolycopersici comb. nov. This extends the potential host range of E. aquilegiae complex to the plant family Sapindaceae. We conclude that awareness of the host associations of PMs can potentially benefit crop disease management.

Oidium longipes, A New Powdery Mildew Fungus on Petunia in the USA: A Potential Threat to Ornamental and Vegetable Solanaceous Crops

This is the first North American report of Oidium longipes, an anamorphic powdery mildew species described recently in Europe. It was found on vegetatively propagated petunia grown in a commercial greenhouse in New Jersey, USA, where it caused a rapidly spreading disease. The pathogen might have originated offshore and may have already been distributed in the United States through horticultural trade. During field surveys in Europe, it was found on petunia in Hungary and Austria as well; this is the first report of O. longipes from these two countries. A detailed light microscopy study of American and European specimens of O. longipes, including freshly collected samples and authentic herbarium specimens, revealed that its conidiophore morphology is more variable than illustrated in the original species description or in subsequent works. Microcycle conidiation, a process not yet known to occur in powdery mildews, was repeatedly observed in O. longipes. The rDNA internal transcribed spacer (ITS) sequences were identical in colonies containing different conidiophore types as well as in a total of five specimens collected from petunia in the United States, Austria, Hungary, Germany, and Switzerland. A phylogenetic analysis of the ITS sequences revealed that the closest known relative of O. longipes is O. lycopersici, known to infect tomato only in Australia. Cross-inoculation tests showed that O. longipes from petunia heavily infected tobacco cv. Xanthi, while the tomato and eggplant cultivars tested were moderately susceptible to this pathogen. These results indicate that its spread represents a potential danger to a number of solanaceous crops. Our ad hoc field surveys conducted in 2006 and 2007 did not detect it outside New Jersey in the United States; all the other powdery mildew-infected petunias, collected in New York and Indiana, were infected by Podosphaera xanthii. In Europe, most of the powdery mildew-infected petunias examined in this study were infected by P. xanthii or Golovinomyces orontii. Our multiple inoculation tests revealed that the same petunia plants and even the same leaves can be infected concomitantly by O. longipes, O. neolycopersici, G. orontii, and P. xanthii. Thus, it is at present unclear to what extent O. longipes contributes to the powdery mildew epidemics that develop year after year on solanaceous plants in many parts of the world.