Molecular identification of anamorphic powdery mildews (Erysiphales)

The powdery mildew fungi (Erysiphales) are a common group of obligate plant pathogens that can be extremely difficult to identify, depending on the reproductive stage encountered. The ribosomal DNA Internal Transcribed Spacer ( ITS) region was assessed for its usefulness to link anamorphic Erysiphales with their respective teleomorphs. PCR primers for the rDNA ITS region were designed and found to have enhanced specificity for the 12 genera tested, even in the presence of contaminating fungi. Recent herbarium specimens of both anamorphic and teleomorphic material yielded sufficient DNA for amplification using a Chelex-based extraction method. The ITS regions from 25 anamorphic specimens were sequenced and compared with the ITS sequences of their suspected teleomorphs. In most cases, an ITS region sequence similarity of above 99% indicated that a correct match had been made, although a specimen on Phlox could not be identified and a somewhat unexpected match was made between a specimen on Convolvulus and the celery powdery mildew (Erysiphe heraclei). Although this technique will not always unambiguously identify an anamorphic specimen, it will provide valuable information to use in conjunction with morphological and host range data to aid in the final identification.