First Report of Sphaeropsis tumefaciens on an Endangered St. John's-Wort in Florida

Edison's St. John's-Wort (Hypericum edisonianum (Small) Adams & Robson) is a state-endangered, clonal, endemic shrub found in seasonal ponds in DeSoto, Glades, Highlands, and Polk counties in Florida. In 1998, a population of H. edisonianum with large (2 to 6 cm long), abnormal growths on stems was observed. Initial gall symptoms were rounded swellings beneath undisturbed bark. With age, these galls became irregular in shape, and the bark became fissured with occasional witches' broom. Galls were collected, and surface-sterilized fragments were cultured on acidified potato dextrose agar. Cultures were uniformly black with pycnidia and oblong, nonseptate, or one-septate, hyaline conidia. The fungus was identified as Sphaeropsis tumefaciens Hedges. Shallow stem cuts were made in plants with a sterile scalpel, and small pieces of the fungal culture were inserted and wrapped with Parafilm. Small swellings at the wound site were observed within 8 weeks on fungus-inoculated plants. Maximum growth of stem galls was 1 cm in length on stems after 1 year. S. tumefaciens was consistently reisolated from galls. There were seven replicate plants (with controls) in each of three experiments with similar results. To our knowledge, this is a new host record for S. tumefaciens, a widespread fungal pathogen in Florida. Under the drought conditions of 2000, wild plant populations without infection had as much as 48% mortality, while the population infected with S. tumefaciens had 83% mortality.