1981 Volume 47 Issue 4 Pages 449-456
Pythium spp. were isolated from soils and roots of various plants collected in the northern (Tohoku district) and southern (the Ryukyu Islands) parts of Japan that were studied for the distribution, kinds of species, and the populations. Isolations of Pythium from soils were conducted by the trapping method using cucumber, lupin, and corn seeds as trapping substrates, and a modification of Waksman's direct inoculation method using water agar as an isolation medium. Pythium spp. were found in 25 out of 27 soil samples of Tohoku district, and all of 21 samples of the Ryukyu Islands. Kinds of Pythium spp. were different according to the temperatures at the isolation procedure by the trapping method. Pythium aphanidermatum with an optimum temperature of 35C occupied 10 out of 43 isolates obtained at 36C and one out of 150 isolates at 20 and 7C for Tohoku isolates, whereas for the Ryukyu isolates, it occupied 37 out of 106 at 24C, but no isolate was obtained at 7C. This fungus was also isolated from 6 out of 11 plant species collected in both districts. A total of 52 plant isolates, 37 from Tohoku district and 15 from the Ryukyu Islands, were studied on temperature responses and it was found that Pythium spp. with high optimum temperatures for growth were more abundant in the latter isolates than in the former. Quantitative data were obtained by the modified direct inoculation method, and there were less than 50 propagules of Pythium spp. per g of soil, 51-200, and 201-1040 in the respective 19, 17, and 12 out of 48 samples assayed. Isolates of Pythium from soils and roots of various plants in both districts were identified at least to 13 and 8 species, respectively.