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Analysis of Factors That Influence the Epidemiology of Sclerotinia minor on Peanut

In North Carolina, sclerotia of Sclerotinia minor germinate myceliogenically to initiate infections on peanut. The effects of soil temperature and soil matric potential (ψ_M on germination and growth of S. minor have not been well characterized, and little is known about relative physiological resistance in different parts of the peanut plant. Laboratory tests examined the ability of the fungus to germinate, grow, and infect detached peanut leaflets at soil temperatures ranging from 18 to 30°C at ψ_M of -100, -10, and -7.2 kPa. In addition, detached pegs, leaves, main stems, and lateral branches from three peanut lines varying in field resistance were examined for resistance to infection by S. minor. Sclerotial germination was greatest at 30°C and ψ_M of -7.2 kPa. Final mycelial diameters decreased with decreasing ψ_M, whereas soil matric potential did not affect lesion development. Mycelial growth and leaflet lesion expansion were maximal at 18 or 22°C. Soil ψ_M did not affect leaflet infection and lesion expansion. Lesions were not observed on leaves incubated at temperatures of 29°C or above, but developed when temperatures were reduced to 18 or 22°C 2 days after inoculation. Pegs and leaflets were equally susceptible to infection and were more susceptible than either main stems or lateral branches. Results of this work, particularly the effects of temperature on S. minor, and knowledge of peanut part susceptibility has application in improving Sclerotinia blight prediction models for recommending protective fungicide applications.