Pleomorphism in Ceratocystis ulmi: chlamydospore formation

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Abstract
Conditions are described for the synchronous production of chlamydospores from both the yeast and mycelial phases of Ceratocystis ulmi, the causative agent of Dutch elm disease. In a defined liquid medium the pH value is critical. Chlamydospores are formed from pH 2 to pH 3 but not above pH 3. The chlamydospores are fully viable and reproduce via germination following a 2-month aging period. The chlamydospores formed from yeasts and mycelia differ, however, with respect to both cell wall chemistry and size (Y = 5.1–9.2 μm; M = 10.9–12.7 μm). A morphological-phase diagram is presented depicting the complete developmental potential of C. ulmi.