VIEW ARTICLE

Verticillium albo-atrum: Quantitative Isolation of Microsclerotia From Field Soils. O. C. Huisman, Assistant Professor, Department of Plant Pathology, University of California, Berkeley 94720; L. J. Ashworth, Jr., Plant Pathologist, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 64:1159-1163. Accepted for publication 26 March 1974. DOI: 10.1094/Phyto-64-1159.

Microsclerotia of Verticillium albo-atrum were quantitatively isolated from field soils by a density flotation procedure. Organic residues were obtained by wet-sieving soil samples and subjecting the 37 to 125 µm soil fraction to density flotation in 65% sucrose (w/w). The sucrose flotation was less effective (70%) and gave more variable results in determining populations of Verticillium in soils than the direct plating of wet sieved residues, but the flotation method allowed direct isolation of microsclerotia. With the aid of a dissecting microscope, microsclerotia-like structures were individually removed from the sucrose flotation residue for separate plating. Nearly 100% of the Verticillium detected by our assay was present as microsclerotia. All the microsclerotia had small bits of plant organic material associated with them. A significant number of the microsclerotia were also present in small clusters of two or more. Assuming that all microsclerotia-like structures were Verticillium, minimum viability values ranged from 5 to 50%.