ARS | Publication request: Lesion expansion of Sclerotinia minor and S. sclerotiorum on two peanut cultivars

Submitted to: American Phytopathological Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2009
Publication Date: August 2, 2009
Citation: Brown, M., Melouk, H.A., Hunger, R., Conway, K. 2009. Lesion expansion of Sclerotinia minor and S. sclerotiorum on two peanut cultivars [abstract]. Phytopathology 99(6):S17. Available: http://www.apsnet.org/meetings/2009/abstracts/a09ma96.htm.

Technical Abstract: Inoculation of peanut stems with Sclerotinia minor (SM) or S. sclerotiorum (SS) causes Sclerotinia blight, which is characterized by the formation of tan, water-soaked lesions on infected plant parts, leading to tissue collapse and necrosis of the affected tissue. Significant losses occur in Oklahoma when Sclerotinia blight is severe, or the disease is not managed properly. Considerable information is known about the reaction of SM on peanut, but less is known about the reaction of peanut to SS. The purpose of this research was to quantify the rate of lesion expansion (RLE) on Okrun, a cultivar susceptible to SM, and Valencia C, a cultivar moderately resistant to SM. Stems of 6 to 8 week old plants were inoculated at midpoint with mycelial plugs from two-day-old Sclerotinia cultures (two SS isolates from peanut and pumpkin, and one SM isolate from peanut) grown on potato dextrose agar with 100 mg/L streptomycin sulfate. Plants were then placed in clear, polyethylene humidity chambers (>95% RH) for 7 days. Lesion length measurements were taken at 3, 4, 5, 6, and 7 days after inoculation. RLE (cm/24 hr) on Okrun were 2.62 for SM peanut, 2.53 for SS pumpkin and 0.56 for SS peanut with an LSD0.05 of 0.30. RLE on Valencia C were 1.78 for SM peanut, 2.37 for SS pumpkin, and 0.11 for SS peanut with an LSD0.05 of 0.36. These results demonstrate that SS from peanut was the least virulent, and indicate the importance of isolate selection in testing of pathogenicity.