Calcium-Dependent, Genus-Specific, Autoaggregation of Zoospores of Phytopathogenic Fungi

Reid, B., Morris, B. M., and Gow, N. A. R. 1995. Calcium-dependent, genus-specific, autoaggregation of zoospores of phytopathogenic fungi. Experimental Mycology , 19, 202-213. Dense populations of zoospores of Phytophthora palmivora , Pythium catenulatum, and Pythium dissotocum formed multicell clumps, or autoaggregates. Autoaggregation was the result of active taxis and was shown to be density-dependent, calcium-requiring, and influenced by pH. In addition, autoaggregation appeared to be species-specific, since aggregates of Ph. palmivora did not attract zoospores of three Pythium species and aggregates of Py. catenulatum did not attract Ph. palmivora zoospores. Aggregation centers generated a calcium ion gradient and induced chemotropic growth of germ tubes emerging from zoospore cysts. Autoaggregation also functions to enhance zoospore accumulation at plant root surfaces, thereby increasing inoculum potential for infection. In the absence of roots, autoaggregation may enhance zoospore population survival.