Examinations of nuclear behaviour during sexual cycle in the diplontic oomycete Phytophthora palmivora (Butl.) Butl

Nuclear behaviour during gametangial- and oospore development in Phytophthora palmivora was studied by light-, fluorescence-, and electron microscopy. After contact between oogonial and anther-idial initials, the antheridial initial is penetrated by the oogonial initial. The latter expands and nuclei and cytoplasm stream into it. After the delimitation of gametangia, a number of nuclei degenerate, the rest proceed through two gametic meiotic divisions both in the antheridium and the oogonium. Three of the meiotic products from each nucleus degenerate. The oogonium is penetrated by the antheridial fertilization tube and nuclear fusion occurs. The oosphere forms, then the periplasm degenerates, and the oospore wall builds up. Upon release of zoospores diploid mycelia are produced.