Association of bacteria with sporangium formation and breakdown of sporangia in Phytophthora spp

Abstract

Leachates from different soils extracted at similar moisture potentials varied in their ability to induce sporangium formation, zoospore release and sporangium breakdown in Phytophthora spp. Sporangium production by P. cinnamomi did not occur in soil leachates heated at 40–50°C for 10 min or in soils treated with steam-air at 60° for 30 min. No evidence was obtained that Pseudomonas or Chromobacterium spp. were involved in the induction of sporangium formation. Chemotaxis of bacteria to sporangia occurred at zoospore release. Where sporangial breakdown occurred, the chemotaxis persisted for a longer period as the cytoplasm was withdrawn from the sporangial wall to be released eventually, without zoospore formation, through the papilla. The bacteria were oriented at right angles to the sporangial wall. Electron micrographs showed that in the vicinity of a bacterium, the outer, thin, electron-dense layer of the sporangial wall had disappeared and the cytoplasm of the sporangium had withdrawn from the cell wall.