Identification of the Pathogen of Powdery Mildew Disease on Dandelions

Powdery mildew diseases are widespread and the group of causal pathogens has a broad host range. Many powdery mildew diseases are caused by pathogens in the Erysiphaceae which consists of 16 genera and approximately 650 species. Powdery mildew was observed on common dandelion (Taraxacum officinale), collected in Fayetteville, AR, and was identified using morphology and ITS DNA sequences. Chasmothecia were observed on the leaf surface and were subglobose, 30-35 µm in diameter, and scattered in patches. Asci were oblong, 12-16 µm long, 8- 10 µm wide, and enclosed in chasmothecia with ascospores inside. For sequence analysis, three primers were used:  (1) the primer ITS1/4 amplifying 563 bp DNA fragment including partial 18 S ribosomal RNA gene and complete sequence of ITS1 the 5.8 S ribosomal RNA gene, ITS2, and partial sequence of the 28 S ribosomal RNA gene; (2) the powdery mildew specific primer PMITS1/2 amplifying 696 bp DNA fragment including full sequence of 563 bp DNA fragment amplified by ITS1/4; and (3) the primer ctw13/tw14 amplifying 280 bp DNA fragment including partial sequence of 28 S ribosomal RNA. The sequences were blasted in GenBank. All three sequences from dandelion powdery mildew had 100% similarity to Podosphaera erigerontis-canadensis (GenBank: AB525916) which was identified from dandelion (T. officinale) in Japan. Phylogenetic analysis was performed by using ITS sequences of other powdery mildew fungi from different plants.