Submitted to: North American Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2013
Publication Date: 1/3/2013
Citation: Dugan, F.M. 2013. Golovinomyces spadaceus causing powdery mildew on Coreopsis hybrid 'Full Moon' (Heliantheae, Asteraceae) in Washington State. North American Fungi. 8(1):1-3.
Interpretive Summary: Coreopsis cultivars are popular ornamentals. Powdery mildew is a troublesome disease of these flowering plants. However, current references to powdery mildew of Coreopsis do not specify species or use obsolete taxonomy, thereby obscuring knowledge of host range and epidemiology of the pathogen. To facilitate management, and to bring taxonomy and nomenclature up to date, this note is issued regarding the identity and current nomenclature for the powdery mildew Golovinomyces spadiceus on the cultivar 'Full Moon.'
Technical Abstract: Symptoms of powdery mildew were observed on a Coreopsis cultivar in the Horticulture and Landscape Architecture Garden on the Washington State University campus, Pullman, Whitman County, Washington. White to off-white sporulating mycelial areas were ~5mm in diam to confluent and confined to adaxial surfaces of leaves. Hyaline, short-cylindrical to ovoid conidia, 24-40 x 13-19 µm and lacking fibrosin bodies were formed in chains. Conidiophores were ~65-100(-125) with foot cells ~30-70 x 10-13 µm and usually with 2-3 cells between the foot cell and the basal conidium. Appressoria were papillate, ~4-5 µm in diam. Conidial germination was of the Euoidium type, apical to sub-apical, with germ tubes ending in club-shaped or swollen appressoria. Chasmothecia were not seen. The host was documented as Coreopsis ‘Full Moon’'a cross between C. rosea Nutt. and an interspecific hybrid of unspecified parentage. The specimen keyed to Golovinomyces sect. Golovinomyces and the conidial state matched the description of Golovinomyces spadiceus. This note is issued to report occurrence of G. spadiceus on Coreopsis ‘Full Moon,’ to advise diagnosticians and others of the desirability of applying the name G. spadiceus to isolates from Coreopsis previously considered G. cichoracearum, and to provide clear photomicrographs of diagnostic characters distinguishing G. spadiceus from Leveillula, Podosphaera and other species of Golovinomyces with hosts in the Heliantheae.