1. This paper deals with the results on seed treatment of Astragalus sinicus L. with sulphuric acid solution for destroying the sclerotia of Sclerotinia trifoliorum Eriks. contaminating the seeds. 2. Commercial seeds of A. sinicus in Japan have contained sclerotia of S. trifoliorum from 90 to 350 or more in number per 100ml of the seeds. 3. The larger the sclerotia, either scratched with sand or not, the greater the germination by apothecia, while the smaller sclerotia decayed more easily during germination. 4. The minimum volume of acid solution for treating seeds was about 60 per cent of the volume of the seeds. The seeds treated with 7 or 8 per cent solution of sulphuric acid for 3.5 and 4.0 hours gave a higher percentage and greater energy of seed germination than those of untreated seeds. Moreover almost all the sclerotia treated decayed and degenerated, and did not germinate by apothecia, while with untreated sclerotia 95-97 per cent of the sclerotia used germinated. In field experiments, the treated seed plots were free from disease at all, but the untreated seed plots were severely diseased. Preliminary experiments showed that the yield from treated seeds was as much as 3 times greater than that of untreated seeds. 5. From above data, we should expect good results for destroying the sclerotia mixed with the seeds of A. sinicus, by seed treating for 3.5 to 4 hours with 7 or 8 per cent solutions of sulphuric acid.
1. Since the antibacterial effect of cellocidin on X. oryzae was antagonized by cysteine and glutathione, cellocidin was considered to interact with -SH groups. 2. The oxidation of various intermediates of the Krebs' cycle by the cell-free extracts of X. oryzae, prepared by sonic oscillator, and also the effect of cellocidin on the oxidation, were studied by measuring the reduction of triphenyl tetrazolium chloride. It was found that cellocidin at the minimum growth-inhibitory concentration (10ppm) inhibited selectively NAD requiring dehydrogenases, such as α-ketoglutarate dehydrogenase, glutamic dehydrogenase, and malic dehydrogenase, but did not inhibit NAD non-requiring dehydrogenases, such as succinic dehydrogenase and urease. 3. Effect of cellocidin on oxygen uptake by cell-free extracts of X. oryzae prepared by sonic oscillator, was studied in the presence of related metabolic intermediate of the Krebs' cycle as substrates. It was found that the oxygen uptake was inhibited by cellocidin at a concentration of 100mcg/ml when substrates such as α-ketoglutarate, iso-citrate etc. which require NAD as co-enzyme for oxidation, were used, but was not inhibited when succinate was used as substrate. 4. Effect of cellocidin on the system α-ketoglutarate→succinate, of X. oryzae, was studied. When the oxidation of succinate was inhibited by the addition of malonate, the oxidation of α-ketoglutarate, in the presence of NAD, by cell-free extracts of X. oryzae, was inhibited by cellocidin at a concentration of 1mcg/ml, which is smaller than the minimum growth-inhibitory concentration. Therefore cellocidin was considered to be an inhibitor on the system α-ketoglutarate→succinate. 5. Cellocidin, at a concentration of 100ppm, did not inhibit electron transport system, such as NADH2 oxidase and NAD reductase, of cell-free preparations of X. oryzae. 6. The incorporation of 14C-amino acids into the protein fraction of X. oryzae was not inhibited by cellocidin at a concentration of 10ppm.
Fungicidal properties of methyl bromide was studied with spores of Penicillium islandicum, the fungus of yellowsis rice grains. Spore mortality was assessed under microscope in most case, but colony counting on Koji extract agar in petri dish was also applied in case of high mortality. The fungicidal effect increased with temperature. Spore mortality attained 100 per cent within 72hrs., at temperatures from 15° to 30°C. Probit of mortality plotted against logarithm of fumigation time yielded straight lines, the slopes of which being almost constant at a given air humidity, irrespective of temperature and gas concentration. The fungicidal effect did not appreciably change with air humidity.
1. Thirty two species of leguminous plants were inoculated with the sap from the young shoots of Satsuma orange showing symptoms of Satsuma dwarf. Nine species including cowpea (Vigna sinensis Endl.), asparagus bean (Vigna sesquipedalis Wight), kidney bean (Phaseolus vulgaris L.), Crotalaria spectabilis Roth, peanut (Arachis hypogaea L.), garden pea (Pisum sativum L.), Chinese milk vetch (Astragalus sinicus L.), sword bean (Canavalia gladiota DC.), and Japanese clover (Microlespedeza striata Makino) were proved to be susceptible to a virus present in the affetced trees. Two species of Chenopodiaceae and three species of Cucurbitaceae were not subject to it. The authors temporarily propose the name “Satsuma dwarf virus” to this legume infecting virus. 2. Among the susceptible plants listed above, Blackeye cowpea and kidney bean (Satisfaction) showed the most characteristic symptoms. The former showed mottling and vein clearing on the leaves, and necrotic streaks on the petioles as well as on the stems. The latter also developed clear mottling and vein clearing on the foliage of most plants that were infected by sap-inoculation. These two species appear to be good indicator plants. However, retransmission from infected legume plants to Satsuma orange has not been successful in the tests so far conducted. 3. Higher percentages of infection resulted when the expressed sap was buffered with about an equal volume of 0.05-0.1mol solution of K2HPO4. 4. One-month old shoots of affected Satsuma orange were demonstrated to carry highly active virus in the leaves, bark and wood portions. One-year old shoots and relatively old current shoots carried active virus in the wood, but not in the bark of twigs or the leaves.
From the results of the previous experiment on the crown rot of sugar beet in Hokkaido, it was pointed out that Rhizoctonia solani in the soil of sugar beet field becomes active in two different seasons of a year, i.e., usually May to June and July to August. The reason of the fluctuation of the fungus activity in soil was considered by the senior author to be due to alternation of different strains of R. solani in the soil depending on the advance of season. In the present experiment, the range of Rhizoctonia strains in a particular soil of flax field, and their comparative characteristics were studied. Isolations of the causal Rhizoctonia were made from May to August in the flax growing plots of the University Farm in Sapporo. More than 150 isolates were obtained from affected flax tissues and also about 100 cultures were isolated from the soil by means of the flax trap technique. All of them could be divided according to their cultural characters into two apparent groups: one called “spring strain” was isolated from the soil and damped-off seedlings in May and June; the other, “summer strain”, was obtained in July and August from the soil and lesions on the stems of flax at the post-flowering stage. Comparative studies were carried out with several isolates each of the two strains. The effect of temperature on the growth and pathogenicity of both strains is quite different: the temperature which induces the fastest mycelial growth of the spring strain on PDA (Table 3) or through soil-tubes (Fig. 1) is generally lower than that in the summer strain. The spring strain causes severe damping- off at low temperature such as 13°and 18°C (Figs. 2, 3). The results of pathogenicity trials on the flax of different ages (Tables 4, 5, 6) proved that the pathogenicity of strains is specialized by the age of the host plant: isolates of the spring strain are pathogenic only to young seedlings and can not attack mature plants, while those of the summer strain are slightly pathogenic on seedlings, but readily invade mature stems of flax in the post-flowering stage. The results of isolation experiments from the soil which was artificially inoculated with both strains showed that all of the isolates caught by the flax trap from the soil incubated at low temperature (5°to 18°C: average 13°C) and of those isolated from infected host plants which were grown under the same condition, were found to belong to the spring strain; when the soil was kept at higher temperature (12°to 28°C: average 20°C) both strains were obtained from the soil and host plants (Tables 7, 8). The cultural characters of all isolates of each strain are quite uniform, but there are remarkable differences between the two strains. The spring strain is identified as Pellicularia filamentosa from its morphological character as well as from the perfect stage formed on the flax stem and the surface of soil particles in the experimental plots during the isolation experiments in May and June. Because of the lack of perfect stage and of a few differences in its vegetative characters from the original description, the summer strain cannot be clearly identified as Pellicularia praticola. On this account the authors propose the name Rhizoctonia solani, the classic complex species, to cover the both strains.