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A Method of Quantifying Numbers of Microsclerotia of Verticillium albo-atrum in Cotton Plant Tissue and in Pure Culture. S. D. Tsai, Research Associate, Department of Plant Pathology, University of California, Riverside 92502; D. C. Erwin, Professor, Department of Plant Pathology, University of California, Riverside 92502. Phytopathology 65:1027-1028. DOI: 10.1094/Phyto-65-1027.

Cotton leaves containing microsclerotia of Verticillium albo-atrum were blended in water, and the suspension was passed through sieves of different pore sizes. Microsclerotia of different sizes (< 37 µm, 37 to 125 µm, and > 125 µm) were collected and counted microscopically in a Hawksley eel worm counting chamber. Comparisons of different numbers of blending periods (15 seconds) indicated that the maximum number of unbroken microsclerotia (37 to 125 µm fraction) was obtained after two to three 15-second periods (30-45 seconds). The number of microsclerotia in the 37 to 125-µm fraction from a pure culture was determined to be inversely correlated colorimetrically with the percentage of light transmittance at 400 nm. These techniques were useful for quantitative research.

Additional keywords: colorimetry, counting chamber, inoculum.