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The Influence of Milling of Air-Dry Soil Upon Apparent Inoculum Density and Propagule Size of Verticillium albo-atrum. L. J. Ashworth, Jr., Department of Plant Pathology, University of California, Berkeley 94720; D. M. Harper(2), and H. L. Andris(3). (2)(3)Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 64:629-632. Accepted for publication 5 November 1973. DOI: 10.1094/Phyto-64-629.

Microsclerotia of Verticillium albo-atrum in air-dry field soil equilibrated in 1 week at 80% relative humidity (RH), and in soil air-dried for 48 h at 22-25 C and 40% RH, were unaffected by various soil milling procedures. But microsclerotia in soil stored at 40% RH (room conditions) for 4.5 mo before milling, were broken into smaller units regardless of milling procedure. Milling procedures in decreasing order of microsclerotium breakage were mortar and pestle, high-speed micromilling (20,000 rpm), and a 2-mm sieving. The data indicate that microsclerotium breakage, depending upon soil storage conditions and milling procedures, can result in apparent inoculum densities greater than the actual inoculum densities of field soils.

Additional keywords: soil-borne pathogens.