Identity of a powdery mildew fungus occurring on Paeonia and its relationship with Erysiphe hypophylla on oak

A powdery mildew fungus found on Paeonia lutea at the Botanical Garden of Geneva (Switzerland) was identified as Erysiphe hypophylla based on morphological observations. The occurrence of E. hypophylla on Paeonia seemed curious, because host plants of this species have been restricted to a few Quercus species of the family Fagaceae. In this study, we determined the rDNA sequences of the powdery mildew specimens on Paeonia and E. hypophylla on Quercus to confirm the identity of the Paeonia fungus. The three sequences from the specimens on P. lutea were identical to one another in both ITS and 28S rDNA regions and also to the sequences of E. hypophylla on Q. robur, which supports the identification that the fungus on P. lutea is E. hypophylla. However, these sequences were also identical to the sequences of E. alphitoides on Quercus spp. and Oidium mangiferae on mango. This result suggests a possibility that E. hypophylla is conspecific to E. alphitoides. Further study is required to clarify whether E. hypophylla is a synonym of E. alphitoides or a distinct species.