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Cephalosporium gramineum Populations in Soil Under Winter Wheat Cultivation. M. V. Wiese, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824; A. V. Ravenscroft, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 65:1129-1133. Accepted for publication 29 April 1975. DOI: 10.1094/Phyto-65-1129.

Effects of seasonal variations and cultural practices on the number, distribution, and longevity of Cephalosporium gramineum propagules in wheat field soil were monitored using a selective culture medium assay. Monthly assays over a 2-year period in fields under continuous winter wheat cultivation and with a history of Cephalosporium stripe disease, detected distinct periods of high and low soil populations of the causal fungus. Highest soil levels (normally exceeding 100,000 propagules/g fresh weight) were detected between October and February and resulted from the development of the saprophytic, sporodochial stage of the fungus, Hymenula cerealis, on infested host residue on the surface and in the upper 7.6 cm (3 inches) of soil. Residue deterioration, short conidial longevity, and limited saprophytic activity at higher temperatures markedly reduced soil populations during early spring so that typically <5,000 propagules/g were present from May through July. Removing straw or plowing it under, as opposed to disking it into the soil prior to planting, reduced fungus levels and the incidence of Cephalosporium stripe disease. Infested straw beneath the soil surface supported the multiplication of H. cerealis during the first autumn but was degraded and nonsupportive by the second. However, straw undisturbed on the soil surface decayed slowly and supported the saprophyte during fall and winter for three consecutive years. Propagules in moist field soil screened of residue and held at 23 C and 7 C, respectively, had a half life of 1 and 26 weeks. Such propagules had a capacity to multiply at 7 C, but not at 23 C or in dry soil.