Morphology of Phytophthora cinnamomi

SUMMARYThe morphology of Pc40 (A2) and Pc97 (A1) isolates of Phytophthora cinnamomi was studied with light and scanning electron microscopy. While confirming the findings of previous workers, some interesting features were observed, hitherto undescribed. Encysted zoospores germinated either by germ tubes or “repeated emergence” of zoospores. Microsporangia or miniature sporangia and appressoria were sometimes produced by germ tubes. Bicellular antheridia were present in both Pc40 selfing and in Pc40 × Pc97. They were longer than the unicellular type and occurred less frequently. The amphigynous antheridium was presumably brought about by the penetration of an antheridium initial by the oogonium initial. A fertilization tube was clearly demonstrated within the oogonium stalk. Oogonia and oospores from Pc40 selfing were larger than those from Pc40 × Pc97. Isolate Pc40 produced more sporangia than Pc97 and the Pc40 sporangia tended to be longer and limoniform. The significance of the bicellular antheridium and the use of scanning electron microscopy in the taxonomy of Phytophthora are discussed.