VIEW ARTICLE

Ecology and Epidemiology

Comparative Morphology and Survival of Chlamydospores of Fusarium roseum ‘Culmorum’ and ‘Graminearum’. J. W. Sitton, Agricultural research technician, U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, Pullman, WA 99164; R. James Cook, research plant pathologist, U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, Pullman, WA 99164. Phytopathology 71:85-90. Accepted for publication 15 June 1980. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1981. DOI: 10.1094/Phyto-71-85.

Macroconidia of both Fusarium roseum ‘Culmorum’ and ‘Graminearum,’ added to nonsterile soil, converted after 4–7 days to thick-walled chlamydospores. Both fungi formed double-walled chlamydospores (as viewed in thin-section by transmission electron microscopy) in macroconidia exposed for 4 days to soil extract solution at 25 C. Although morphologically indistinguishable, the chlamydospores of Graminearum, but not those of Culmorum, were killed by rapid air drying, by a 35-sec exposure in moist soil to 20 kW microwave treatment, and by incubation for 2–4 wk in moist soil at 35 C. Nearly all chlamydospores of Culmorum incubated in air-dry soil at 9 C were alive after 8.5 yr, whereas those of Graminearum declined steadily in number and were finally eliminated by natural attrition after 5.5 yr. Greater resistance to adversity may explain why, in the Pacific Northwest dryland wheat area, Culmorum persists in many fields and is consistently recovered by dilution-plating, whereas Graminearum has not yet been recovered by dilution-plating.