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Not just Botrytis: multiple fungal pathogens cause leaf spots on peony in the United States
A. R. GARFINKEL (1), G. A. Chastagner (1). (1) Washington State University, Puyallup, WA, U.S.A.

The herbaceous peony (<i>Paeonia lactiflora</i>) is grown as a high-value cut flower crop and landscape plant worldwide. Through interactions with peony growers, we found that many perceive Botrytis gray mold as a significant production and post-harvest issue at their farms. In a survey to determine the cause of leaf spots on peony, we acquired infected foliage from commercial growers and through visual scouting of peony plantings throughout the United States with an emphasis on Washington, Oregon, and Alaska. Using morphological and molecular methods, we identified multiple fungal pathogens never before reported on peony in the United States in addition to the commonly-reported pathogens, <i>Botrytis</i>, <i>Cladosporium</i>, and <i>Alternaria</i>. The discoveries of one of these pathogens, <i>Mycocentrospora acerina</i>, in Washington and Alaska represent only the second and third reports of this pathogen infecting peony in the world. The detection of <i>Pilidium concavum</i> in North Carolina is the first report of this pathogen on peonies outside of East Asia. We also identified a complex of <i>Botrytis</i> species infecting peony, of which at least one species is undescribed and appears to be unique to Alaska peony production. Clearly, a wider range of fungal pathogens, including multiple species of <i>Botrytis</i>, infect peony than is indicated in the common literature, such as extension bulletins and growers’ guides. These diseases are going misdiagnosed by growers, potentially hindering disease management.

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