First Report of a Leaf Spot on Perennial Peanut Caused by Sclerotinia homoeocarpa . R. J. Hoover, Plant Pathology Department, University of Florida, Gainesville 32611 . T. A. Kucharek, Plant Pathology Department, University of Florida, Gainesville 32611. Plant Dis. 79:1249. Accepted for publication 26 September 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-1249A.
Perennial peanut (Arachis glabrata Benth.) is a tropical legume that was introduced into the United States from Brazil via Florida in 1936. Foci of a leaf spotting disease were present in a stand of perennial peanut cv. Arbrook in 1994 in Marion Co., Florida. The stand was thin and the leaf spots appeared to be associated with weak and dying plants. Neither root rot nor other biological dysfunctions were associated with the debilitated plants. The leaf spots were circular to semicircular to elliptical, tan in the center, and surrounded by a brown to purple ring. They ranged in size from 1.3 to 1.9 cm. Sclerotinia homoeocarpa F. T. Bennett was consistently isolated from lesions on acidified potato-dextrose agar. Bahia-grass (Paspalum notatum Flugge), also infected with S. homoeocarpa, was abundant within the same field. Cultures of 5. homoeocarpa from both plant species were similar in appearance. Plants of three cultivars (Arbrook, Florigraze, and Arblick), and a selection (“Ecoturf”) of perennial peanut and bahiagrass cv. Pensacola were grown in the greenhouse and inoculated with an isolate of 5. homoeocarpa obtained from perennial peanut. Inocula consisted of 3-mm plugs of mycelium that were placed on wounded (cuticle scraped lightly with a scalpel) or unwounded leaflet upper surfaces. Five leaves of each of three plants of the four cultivars of perennial peanut and the bahiagrass were inoculated with and without wounding. Inoculated plants were placed into a transparent moisture chamber with a constant humidity of near 100% for 72 h, after which lesions similar to those seen in the field were observed in both host species. Leaf senesence followed. The incidence of lesions was 98 and 15% across the four entries of perennial peanut for the wounded and nonwounded inoculations, respectively. Consistent isolation of pure cultures of 5. homoeocarpa from lesions on perennial peanut and bahiagrass occurred. Koch’s postulates were again completed in a duplicate experiment. Other fields of perennial peanut with this disease have been found, but it appears to be a disease of little economic consequence when forage is harvested at recommended intervals.