South African Avocado Growers’ Association Yearbook 1990. 13:61-62 A PRELIMINARY REPORT The influence of N and Casources on pathogenicity of Phytophthora cinnamomi and of Ca-sources on resistance of avocado roots to infection by the fungus

Saprophytic growth of Phytophthora cinnamomi indicated that the pathogenicity was not enhanced by addition of Nor Ca-sources to the basal growth medium. Mycelium obtained from the N and Ca-enriched sources and used to inoculate blue lupin seedlings indicated that the pathogenicity of the fungus was reduced by the addition of either N or Ca to the fungus cultures. The detached root technique was used to determine the effect of Ca treatments on the susceptibility of avocado seedling roots cv Edranol to Phytophthora cinnamomi. After treating seedlings for two months with CaCO3 or CaCI2 no difference in resistance could be found.