Effect of Temperature and Moisture Tension on Growth, Sclerotial Production, Germination, and Infection bySclerotinia minor

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Abstract
Sclerotial germination and mycelial growth of S. minor occurred from 6 to 30.degree. C; the optimum for each was at 18.degree. C. Infection of lettuce [Lactuca sativa] tissue by hyphae from germinating sclerotia occurred from 6 to 24.degree. C with an optimum at 18.degree. C. The temperature range for sclerotial formation was from 12 to 24.degree. C with more sclerotia produced at 12.degree. C than at other temperatures, but sclerotia produced at the higher temperatures were larger. Mycelial growth on cornmeal agar occurred at solute potentials of -1 to -73 bars, but sclerotia were formed only within the range of -1 to -43 bars. Growth in liquid media was maximal at about -7 bars and declined at lower solute potentials. Sclerotia produced at various solute potentials and temperatures germinated equally well. Sclerotia were capable of eruptive germination at soil moisture tensions ranging from -1/3 to -15 bars, but the highest percent germination occurred at -1/3 bar. Infection of lettuce tissue by sclerotia at temperatures between 6 and 24.degree. C was dependent on the ability of sclerotia to germinate eruptively. All tissues inoculated with mycelial plugs instead of sclerotia at 6 to 24.degree. C became infected.