VIEW ARTICLE

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.