Sclerotinia minor Jagger is a major pathogen of peanut (Arachis hypogaea L.) in North Carolina, Virginia, Oklahoma, and Texas. Economic crops that are hosts to S. minor are seldom grown in rotation with peanut, and the pathogenicity of S. minor to most weed species commonly found in peanut fields is unknown. In September 2000, signs and symptoms of Sclerotinia infection were observed on plants of yellow nutsedge growing in peanut fields in Bertie County, NC. Fluffy white mycelium, water soaked and bleached areas of the leaves were observed on basal portions of plants. Isolations were made from a symptomatic plant growing in a peanut field at the Peanut Belt Research Station at Lewiston-Woodville, NC. Small portions (1 to 2 cm) of symptomatic leaves were placed on potato dextrose agar (PDA) and pure cultures typical of S. minor were obtained. Small black irregular-shaped sclerotia (<2 mm) were produced abundantly and scattered over the culture surface (1). Pathogenicity was tested by placing agar plugs of mycelium of the fungus between the leaf blades of potted mature yellow nutsedge plants. Plants were misted with water, enclosed in plastic bags, and incubated on a lab counter top at ambient temperature (˜24°C). Mycelia developed after 3 to 4 days and chlorotic leaves appeared by day 7. Sclerotia were observed in 11 days on seedheads, which were distal from the site of inoculation. Uninoculated plants did not develop symptoms. The fungus was reisolated on PDA, and typical cultures of S. minor with small sclerotia were obtained. The nutgrass isolate was inoculated onto detached peanut leaves and typical symptoms developed. This is the first report of yellow nutsedge as a host of S. minor.
Reference: (1) L. M. Kohn. Mycotaxon 9:365--444, 1979.