First report of flower anthracnose caused by Colletotrichum karstii in white Phalaenopsis orchids in the United States.
In October 2010, a Colletotrichum species was isolated from white Phalaenopsis flowers growing in a greenhouse in San Francisco, California, USA. The white petals showed anthracnose-like lesions where necrotic tissue is surrounded by a ring of green tissue. The green halo tissues around the necrotic tissue contain functional chloroplasts. The causal pathogen was identified as C. karstii based on cultural, morphological, genetic (ITS) and pathogenicity analyses. This is thought to be the first report of infection and green island formation caused by C. karstii on orchid flower in the USA.