1987 Volume 53 Issue 4 Pages 507-515
A method for the direct estimation of the number of resting spores of Plasmodiophora brassicae in soil by using a fluorescence microscope is described. After being mixed with tween 80 solution, the soil sample was filtered through sieves to remove coarse minerals and the filtrate was centrifuged. The pellet suspended in distilled water was mixed with a calcofluor white MR2 solution. The mixture solution was examined under a fluorescence microscope and the number of spores was counted. It was very easy to identify spores showing strong fluorescence. This method could be applied to infested soils containing 104 spores/g and slightly less, and also adopted for estimating the number of spores in different soil groups. This improved method has advantages due to the simplicity and shortening of the procedure, the easy enumeration of spores under a microscope and the high recovery efficiency of spores, as compared with the previous methods, and may be of value for practical use. Naturally infested soils in six fields were assessed for the contamination with spore concentrations of up to 105/g.