Inhibition of Germination of Oospores of Peronospora Manshurica

Oospores of Peronospora manshurica have not previously been observed to germinate. In the present tests, however, oospores on seed coats of soybeans washed in running tap water for 1 week germinated. Each germinating oospore produced a germ tube, which developed into typical branched mycelium. Oospores were placed in the center of water-agar plates, some of which were immediately sprayed with a dilute suspension of conidia of P. manshurica. Other plates were sprayed later. Germination of conidia was inhibited in an area around the oospores. The size of the area of inhibition was proportional to the elapsed time between placing oospores on the agar and spraying the agar with conidia. A germination inhibitor has been described for the conidia of P. manshurica and the same inhibitor may be active in preventing oospore germination