QUANTIFICATION OF MICROSCLEROTIA OF VERTICILLIUM-DAHLIAE IN PLANT-MATERIAL BY IMAGE-ANALYSIS

A procedure for the quantification of microsclerotia of Verticillium d ahliae with an image analysis system was compared with counting by eye . Colonised potato plant material was used from plants grown in pathog en-free soil in a greenhouse and from twelve crops (including four pot ato cultivars) grown outdoors in pots filled with pathogen-free soil u nder natural conditions. The values obtained from the potato material from the greenhouse were comparable for both methods. Variation in the results mainly resulted from sampling errors. The numbers of microscl erotia in plants grown outdoors were overestimated by image analysis f or most crops. The source of the error was related to the presence of plant and soil particles that did not discolour during boiling of the samples in sodium hydroxide. Image analysis was a suitable and reliabl e method for assessing the number of microsclerotia only in potato hau lm samples from plants grown in pathogen-free soil in the greenhouse.