Methods for the Extraction of Heterodera Cysts From Not Previously Dried Soil Samples

An elutriator for the separation of cysts from not previously dried soil samples to determine the population density of Heterodera species is described. With this apparatus a mixture of cysts and organic debris is obtained. For further separation this mixture is dried and the cysts are then separated from the debris by flotation with a modification of Buhr's method using water or a mixture of three parts of acetone and one part of carbon tetrachloride. Heterodera cysts differ from practically all other material, found in soil, in that they float for a fairly long time in water after having been dried thoroughly (Fenwick, 1940). In Fenwick's extraction method the soil samples are dried prior to extraction. Cysts are then separated from soil in three steps: first the cysts are concentrated in a small amount of mainly organic material by flotation in-water, then they are separated from most of this material again by flotation in water and finally they are picked from between the soil particles which float as well in water as dry cysts. However, drying whole soil samples, especially when they are large and many must be investigated, requires special equipment or much space. To avoid drying whole soil samples an apparatus was devised for the separa-