Hosta petiole rot (caused by the fungusSclerotium rolfsii var. delphinii) appeared in the northern U.S. within the past decade. Petiole rot is very difficult to control once it appears in a production field or garden, and sclerotia of the pathogen may persist for long periods. Research in our lab by PhD candidate Zhihan Xu seeks to: 1) develop a rapid bioassay to assess cultivar resistance; 2) understand why S. rolsii var.delphinii apparently occurs primarily in the northern U.S. whereas a closely related fungus, Sclerotium rolfsii, occurs primarily in the southern U.S.; and 3) clarify genetic relatedness among phytopathogenic species of the genus Sclerotium.
A previous M.S. student in our lab, Brooke Edmunds, showed that there was a wide range of resistance to the pathogen in 18 popular hosta cultivars (2003,HortTechnology 13:302-305), documented overwinter survival of S. rolfsii var. delphiniisclerotia in Iowa (2003, Plant Health Progress doi:10.1094/PHP-2003-1201-01-RS), and found that the popular herbaceous perennial Pulmonaria is also a host of the pathogen (2003, Plant Disease 87:15). She also conducted field studies testing the effects of type and placement of organic mulch on spread of the disease.