The sexual stage of Phytophthora polygoni Saw.

The sexual stage of Phytophthora polygoni Saw.-which is distinguishable fro m other species of Phytophthora by its inability to grow on common agar med ia, its sporangial characteristics and its disease symptoms-has been succes sfully induced to form sexual organs in diseased leaves collected from the field or by artificial inoculation. The oogonia are smooth, spherical, thin -walled, (28.5-) 33 (-42) mu m diam, with an aplerotic to markedly apleroti c, thick walled (3-4 mu m) oospore, (24.7-) 28.1 (-32.3) mu m diam, and a p aragynous antheridium, 13-25 x 10-15 mu m, attached laterally or apically t o the oogonium. Interesting chlamydospore-like bodies were also observed.