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Influence of Temperature, pH, Osmotic Potential, and Fungicide Sensitivity on Germination of Conidia and Growth from Sclerotia of Colletotrichum coccodes in Vitro. Helene R. Dillard, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456; Phytopathology 78:1357-1361. Accepted for publication 20 May 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-1357.

Germination of conidia of Colletotrichum coccodes was greatest at 22 C after 24 hr. Conidia did not germinate at 7 C after 24 hr and <70% of the conidia germinated at 10 or 31 C. Growth rates of cultures started with air-dried sclerotia were greatest at temperatures from 25 to 31 C. Germination of conidia and growth from sclerotia were optimum at pH 6. Water agar was osmotically adjusted using either KCl, NaCl, CaCl2, or sucrose. Maximum germination of conidia and growth from sclerotia occurred at the highest osmotic potentials (5 to 10 bars). Little or no germination of conidia occurred at 45 bars except when CaCl2 was used to adjust the osmotic potential of the medium. Radial growth from sclerotia was less when KCl or NaCl amendments were used than when CaCl2 or sucrose were used. Sensitivity of conidia and sclerotia to captafol, chlorothalonil, anilazine, mancozeb, and copper hydroxide were determined in vitro. Conidia were most sensitive to captafol, which significantly reduced their germination and germ tube elongation at concentrations of 0.01, 0.1, and 1 μg a.i. ml. Sclerotia were also most sensitive to captafol, which significantly reduced growth at concentrations of 1, 10, and 100 μg a.i./ml. Conidia and sclerotia were sensitive to chlorothalonil at the two highest concentrations tested (0.1, 1 μg a.i./ml and 10, 100 μg a.i. ml, respectively).

Additional keywords: Lycopersicon esculentum, tomato anthracnose.