VIEW ARTICLE

Ecology and Epidemiology

Germinability, Viability, and Virulence of Chlamydospores of Fusarium solani f. sp. phaseoli as Affected by the Loss of Endogenous Carbon. Sachindra Nath Mondal, Doctoral student, Laboratory of Plant Disease Science, United Graduate School of Agricultural Science, Gifu University, 1-1 Yanagido, Gifu 501-11, Japan; Koji Kageyama, and Mitsuro Hyakumachi. Associate professor, and professor, respectively, Laboratory of Plant Disease Science, United Graduate School of Agricultural Science, Gifu University, 1-1 Yanagido, Gifu 501-11, Japan. Phytopathology 85:1238-1244. Accepted for publication 9 June 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-1238.

Chlamydospores of Fusarium solani f. sp. phaseoli progressively lost their endogenous ¹⁴C during incubation on membrane filters on soil, maintained at –1 kPa for 70 days. The endogenous ¹⁴C loss from labeled chlamydospores was comprised of residual ¹⁴C in soil and evolved ¹⁴CO₂. Residual ¹⁴C in soil ranged from 0.2 to 9.6% of the total label. ¹⁴CO₂ evolution from the respiration of chlamydospores and soil microbes accounted for 53.4% of the total label. Soil microbial respiration of exudates of chlamydospores accounted for 15 to 38% of the total residual ¹⁴C (2 to 5% of the total label). Chlamydospore respiration represented 55 to 78% of the total ¹⁴C loss and was the major factor contributing to the loss of endogenous carbon. Chlamydospores were highly germinable (above 90%) in the absence of an external source of nutrients (Pfeffer’s salts solution) when their incubation period on nonsterile soil was 10 days or less, but germinability began to decrease when their exposure to soil exceeded 10 days. Germinability of chlamydospores dropped to zero and virulence significantly declined after incubation on nonsterile soil for 70 days. The linear depletion of ¹⁴C was closely associated with the decline in germinability and virulence of chlamydospores. These results suggest that endogenous nutrient reserves are of importance in establishing a pathogenic relationship between a host and a soil-inhabiting pathogen.