Quantitative detection of <em>Verticillium dahliae</em> in soil as a basis for selection of planting sites in horticulture

Abstract

Verticillium dahliae causes in horticultural production, especially in strawberries and in tree nurseries, high economic damages, which arise from infested planting sites. A detection method is described, which allows the quantification of microsclerotia of the fungus in soil. So it is possible to determine the verticillium infestation level of a planting site und to estimate the disease risk for susceptible crops. Some original results are presented to illustrate the quality of performance of the method. They give evidence that small variations of the quantification procedure have an influence on the detection percentage. In addition the nonrandomly distribution of microsclerotia in soil causes a sample and analysis error, which increases with declining infestation levels. Moreover it is not possible to distinguish the two genotypes V. dahliae and V. longisporum, which show differences in their pathogenicity. Therefore an exact pre-planting disease prediction is difficult, because of the inaccuracy of the detection method and the influence of many unknown soil factors on the infection process. This is the reason why the determination and use of thresholds in practice is critical judged. Nevertheless the quantification of the soil infestation provides growers an opportunity to select verticillium-free sites and to avoid damages.