Synthesis of zoospore peripheral vesicles during sporulation of Phytophthora cinnamomi

Three types of spherical vesicles (dorsal, ventral and large peripheral vesicles) are-found in the peripheral cytoplasm of Phytophthora cinnamomi zoospores. Each is believed to participate in the infection of host plants through formation of a cyst coat, deposition of an adhesive pad or supply of proteins during early germling growth. In the present study, the occurrence of these three vesicles was determined during the asexual life cycle of P, cinnamomi. The vesicles were found to be absent from rapidly growing, vegetative hyphae, but to appear in the hyphae under conditions that induced sporulation. Vesicle formation was correlated with sporulation via the production of sporangia or chlamydospores. In mycelia transferred to nutrient-poor medium, large peripheral and ventral vesicles first appeared about 5 h after transfer; dorsal vesicles appeared about 30 min later. The first sporangia were detected at 7.5 h. Large peripheral and ventral vesicles were also produced before dorsal vesicles in mycelia growing on nutrient agar and in the hyphae formed by germinating cysts. On nutrient agar, the three vesicle types appeared about to h in advance of the development of chlamydospores.