A sclerotia-forming fungus was isolated from a peanut field in eastern New Mexico, where Valencia peanut is grown. The isolated fungus was typified by its darkly pigmented mycelium when grown on culture media, with pigmentation influenced by media. The optimal temperature range for mycelial growth was 20 to 25°C. In pathogenicity tests, the fungus caused water-soaked and light tan lesions on stems at points of inoculation, and lesions progressed up the stems into petioles followed by collapse of leaves. White fluffy mycelium and sclerotia were present on inoculated plants. Based on the examination of morphological and cultural characteristics of sclerotia, apothecia, asci, and ascospores, the isolated fungus with darkly pigmented mycelium on culture media was identified as Sclerotinia sclerotiorum. This study is the first report of S. sclerotiorum on peanut in New Mexico.
Keywords: Sclerotinia blight; dark mycelial; groundnut.