Wet-Sieving Floatation Technique for Isolation of Sclerotia ofSclerotium cepivorumfrom Muck Soil

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Abstract
A wet-sieving floatation technique that facilitates the rapid isolation of sclerotia of S. cepivorum from muck soils was developed. Soil samples (20 g) were washed through 2 stacked sieves (0.595 mm openings over 0.210 mm openings) for at least 5 min, and the residues on the 0.210 mm sieves were transferred to columns containing 2.5 M sucrose solution (1.330 specific gravity]. After 2 h, the soil fractions suspended in the upper portions of the columns were collected, washed with water on 0.210 mm sieves and examined with a dissecting microscope. Sclerotia were removed with forceps, surface sterilized in 0.25% sodium hypochlorite for 2.5 min, washed in distilled water, and cut in half. The 2 halves were placed on potato dextrose agar in petri dishes and kept at room temperature (22-25.degree. C) for 2 wk to allow identification of S. cepivorum. Approximately 82% of sclerotia recovered from naturally-infested soils were confirmed to be S. cepivorum. The specific gravity of laboratory-reared sclerotia was greater than that of sclerotia produced in the field.