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Induction of Chlamydospore Formation in Fusarium solani by Abrupt Removal of the Organic Carbon Substrate. Jane Aldrich Meyers, Research Assistant, Department of Plant Pathology, Washington State University, Pullman, Washington 99163; R. James Cook, Research Plant Pathologist, Plant Science Research Division, ARS, USDA, Pullman, Washington 99163. Phytopathology 62:1148-1153. Accepted for publication 15 April 1972. DOI: 10.1094/Phyto-62-1148.

Sudden withdrawal of exogenous sucrose from the germlings of three clones each of Fusarium solani, F. solani f. sp. phaseoli, and F. solani f. sp. pisi in liquid culture resulted in rapid, synchronous chlamydospore formation. Eight of the nine clones formed chlamydospores within 24 hr; the ninth, a clone of F. solani f. sp. phaseoli from Washington, required 48 hr. Conversely, when sucrose utilization by the nine clones was gradual, and by the fungus itself, chlamydospores formed slowly, and took from 3 to 8 days, depending on the clone. Addition of 1% (w/v) of sterile or nonsterile Ritzville silt loam to the liquid cultures caused earlier and more chlamydospore formation under conditions of gradual sucrose depletion, and more under conditions of sudden sucrose depletion. Adenosine 5' monophosphoric acid (AMP) or 3':5'-cyclic adenosine monophosphoric acid (cAMP) at 103 M also increased the rate and frequency of chlamydospore formation under conditions of gradual sucrose utilization. We propose that depletion of organic carbon as the energy source is the major stimulus to chlamydospore formation in Fusarium solani in natural soil, where rapid growth of microorganisms on the nutrient-coated surface of the conidium causes its abrupt starvation. The possibility of interactions between AMP, cAMP, and energy depletion in chlamydospore formation is discussed.