Abstract
Soil samples from 18 Aphanomyces infested fields were tested by the disease severity index (DSI) method and by direct counting of oospores. There was a curvilinear relationship (r = 0.97***) between DSI and the number of oospores in soil. This was confirmed when a known number of oospores produced in culture were added to non-infested soil. Both assays were suitable techniques for quantifying the inoculum density of Aphanomyces euteiches in soil. The methods could also accurately assess the changes in a population of the pathogen when subjected to experimental soil treatments especially in soil with low DSI values. The Most Probable Number method of estimating inoculum density was less satisfactory.