Morphological and molecular characterization of Podosphaera minor on Spiraea in Iran

Powdery mildew is a common disease of Spiraea spp. worldwide; however, there are no reports of this destructive disease in Spiraea species from Iran.  In recent years, severe powdery mildew symptoms have been observed in Spiraea spp. throughout the Guilan Province. In this study, we collected infected plant specimens and used morphological and molecular approaches to identify the powdery mildew fungus involved in this disease. We did not observe the teleomorphic state of the fungus in this area, and it appears that the fungus occurred only in the anamorphic state. At least six species of Podosphaera occur worldwide, and there is a considerable overlap between the anamorphic characteristics of some species. Hence, the ITS sequence was used to identify common powdery mildew species occurring in Spiraea in the Guilan Province. The results showed that the ITS sequence is useful for Podosphaera species in Spiraea. Podosphaera minor Howe. was identified as the causal agent of powdery mildew disease in this plant. To our knowledge, this is the first report of Podosphaera minor as a fungus in Iran.