Phytophthora drechsleri: Pathogenicity Testing and Determination of Effective Host Range

Abstract

Pathogenicity tests with Phytophthora drechsleri Tucker chlamydospores and different flooding times were conducted on 15 weed and 17 cultivated plant species. Lucerne, safflower and skeleton weed were the only plants that showed a marked response to the pathogen. Lucerne, safflower and soya bean plants were inoculated with agar culture, vermiculite culture or chlamydospores, and their reaction was shown to vary with the type of inoculum used. On the basis of these results, the concept of pathogenicity testing and the results on which the known host range of this fungus is based are examined. It is argued that conclusions drawn from pathogenicity tests are often question- able if the inoculation techniques employed bear little similarity to what may occur in the field. Suggestions for future pathogenicity tests are made.