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Survival of Endoconidia and Chlamydospores of Thielaviopsis basicola as Affected by Soil Environmental Factors. G. C. Papavizas, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705; J. A. Lewis, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 61:108-113. Accepted for publication 28 August 1970. DOI: 10.1094/Phyto-61-108.

A high percentage of chlamydospores of Thielaviopsis basicola survived for at least 4 months in various autoclaved soils and for 2 months in nonautoclaved soils at 45-50% of the moisture-holding capacity (MHC). Soil moisture content was the most important single factor affecting germinability of endoconidia and chlamydospores. Germinability of chlamydospores declined rapidly at 45-50% of the MHC. Decline in germinability was intermediate at 30%; and no decline was observed at 15% and in air-dry soil maintained constantly at 20 C. When the temperature was varied, in air-dry soil germinability was 90% at 10 and 18 C after 3 months, 42% at 26 C, and 30% at 34 C. In moist soil (45-50% MHC), the effect of temperature on germinability was masked by that of soil moisture. In the moist soil at 26 C, germinability dropped to less than 10% after 1 month and to less than 5% after 2 months. Reduction in chlamydospore germinability was not pronounced in wet soil at 10 C. CO2 did not greatly affect chlamydospore germinability in air-dried soil, but had some effect in moist soil. Viability and numbers of endoconidia were greatly reduced by high soil moisture content (45-50% MHC) and high temperature (26 and 34 C).

Additional keywords: Survival, root-infecting fungi, soil moisture.