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First Report of Sclerotinia Blight Caused by Sclerotinia sclerotiorum on Peanut in Georgia

Sclerotinia blight is one of the most economically important diseases of peanut (Arachis hypogaea L.) in Oklahoma and Virginia. Yield losses of 10% are common in these areas; however, losses may exceed 50% in highly infested fields (1). While Sclerotinia minor is considered the primary causal agent, S. sclerotiorum may also incite the disease. Symptoms typically appear late in the season and are favored by cool temperatures and high relative humidity (RH). Initial symptoms include wilting and yellowing of main or lateral branches. Dense mats of white mycelium develop on diseased areas, and small water-soaked lesions are apparent near the soil line. Lesions become bleached and infected tissues have a shredded appearance. Sclerotia are produced on and inside infected plant parts (2). During October 2004, following a period of heavy rainfall and cool temperatures, peanut plants (cv. Tifrunner) with these symptoms were observed in a field near Surrency, GA. The field had been planted to cotton (Gossypium hirsutum L.) for many years and peanut was strip-tilled into a heavy rye (Secale cereale L.) cover. Disease foci were found throughout the field and final incidence was 20%. Stem sections were surface disinfested in 0.5% sodium hypochlorite for 1 min and plated on potato dextrose agar (PDA). Cultures of S. sclerotiorum (2) were recovered after incubation at 20°C for 2 weeks. Pathogenicity tests were conducted by inoculating wounded peanut mainstems with PDA plugs either with or without the fungus. Inoculation sites were wrapped with moistened cheesecloth, and plants were incubated in a dew chamber at 20°C and 95% RH. There were a total of four replications and the experiment was repeated once. Symptoms consistent with those observed in the field appeared after 3 days and lesion lengths were measured after 5 days. Average lesion lengths were 1.4 and 1.6 cm for cvs. Georgia Green and Tifrunner, respectively Controls remained symptomless. Sections of symptomatic tissue were plated on PDA, and S. sclerotiorum was reisolated from 100% of symptomatic tissue. Although S. sclerotiorum is a common pathogen of various winter crops and weeds found in the southeast, to our knowledge, this is a first report of Sclerotinia blight on peanut in the region. No other occurrences of the disease have been reported since the initial discovery; however, potential losses could be incurred if peanuts are planted in infested fields and harvest is delayed.

References: (1) H. A. Melouk and P. A. Backman. Management of soilborne fungal pathogens. Pages 75--85 in: Peanut Health Management. H. A. Melouk and F. M. Shokes, eds. The American Phytopathologicial Society, St. Paul, MN, 1995. (2) D. M. Porter and H. A. Melouk. Sclerotinia blight. Pages 34--36 in: Compendium of Peanut Diseases. 2nd ed. N. Kokalis-Burelle et al., eds. The American Phytopathologicial Society, St. Paul, MN, 1997.