1. From rice plants, one of the growth-stimulating factors for X. oryzae was isolated and it was identified as cystine. The apparent concentration of cystine in rice plants was usually enough to support the growth of the bacterium, yet the concentration of cystine and other sulfur containing amino acids in leaf vessel was uncertain. The biographic properties of the growth-stimulating factors in leaf or root of rice plants seemed to be similar between the resistant and susceptible varieties. 2. Regarding the nutritional requirements of X. oryzae, it seems evident that the bacterium lacks the ability of utilizing inorganic sulfur sources including sulfate, sulfite, thiosulfate and sulfide with or without serine and that the bacterium requires for its growth each one of the sulfur containing amino acids including cysteine, cystine, homocysteine or methionine. 3. In the minimum basal medium, a linear relationship between the growth rate and the concentration of L-cystine added in the medium was observed when logarithmic scale was taken for both axes. 4. The presence of the inhibitory substances which counteract against the growth-stimulating factors in rice plants was recognized. The presence suggested possible mechanism which made the host either resistant or susceptible, yet the host specificity of the bacterium remained unsolved.
Multiplication of ordinary strain of tobacco mosaic virus (TMV) on the duck-weed (Spirodela polyrhiza) was reported in the preceding paper (Komuro and Iwaki 1964). This paper deals with the results of inoculation experiments of several plant viruses and virus strains to the duck-weed. 1. Yellow strain and tomato streak strain of TMV, both isolated from tomato in 1963, were also proved to multiply on the duck-weed without symptom as in the case of ordinary strain of TMV. 2. On the other hands, cucumber mosaic virus, alfalfa mosaic virus, turnip mosaic virus, and also watermelon mosaic virus were not able to multiply on the same weed even in repeated inoculation experiments. 3. Potato virus X (PVX) was ascertained to multiply on the duck-weed from the following experimental results. i) Quantity of PVX recovered from the inoculated duck-weeds on the 3rd day and 5th day after inoculation was small, but it became larger on the 10th and 20th day after inoculation. ii) Vein-clearing sometimes appeared on the fronds of inoculated duck-weed, and the virus was recovered in larger quantities from the fronds showing vein-clearing than from those having no symptoms. iii) Particles, about 500mμ in length, were observed in the juice of fronds inoculated with PVX under an electron microscope, while no such particles were recognized in the juice of healthy fronds. iv) Juice from duck-weed having vein-clearing symptom showed the precipitation reaction when it was mixed with PVX-antiserum. 4. Ordinary strain of TMV, and PVX both multiplied on the duck-weed, when these two viruses were inoculated at the same time, and the fronds of duck-weed showed vein-clearing, as in the inoculation with PVX alone.
Using mulberry seedlings grafted by diseased stems collected from Gumma and Shiga Prefectures, the mode of symptom appearance of mulberry mosaic disease was examined, when temperature was regulated 15, 23 and 31°C, respectively. As a rule, plants grown at 23°C and 31°C showed symptoms while symptoms were almost masked at 31°C. Intensity of symptom at 23°C was higher than that at 15°C. Some of the symptoms on plants kept at 31°C were thickening and hardening of leaves and veinclearing that were considered to be primary symptoms of enation. When plants were kept at 15°C, conspicuous mosaic and a very few ring spot symptoms were shown on leaves. Mosaic was also considered to be primary symptom of enation, because typical enation has further appeared on some of the lightcolored portions of mosaic leaves. Mode of appearance of symptoms on the plants kept at 23°C was very complicated and was variable according to the places collected diseased stems and the growing stage. On the materials from Gumma Prefecture, severe enation developed on the leaves in all growing stage, and few other symptoms were observed. On the materials from Shiga Prefecture, various symptoms, i. e., mosaic, enation, ring spot and yellowing spot, appeared, and transition of appearance of these symptoms showed variation to growing stage.
This paper reports the experimental results on the transmission of potato leaf roll virus by three species of aphids. Virus-free, apterous, adult Myzus persicae Sulz. fed on plants infected with potato leaf roll virus for more than 3 days, transmitted the virus to 50-90per cent of healthy seedlings of Physalis floridana Rydb. when the aphids were tested individually. Rate of transmission was enhanced by increasing the number of the aphid during test feeding. The P. floridana plant infected for two weeks seems to be sufficient as a source of the virus. In order to determine the effect of temperature on the infection, P. floridana plants were inoculated and kept at 18° and 13°C for one month. The plants produced symptoms at 18°C but no symptom was observed at 13°C with the exception of one test plant which developed symptoms 10 days after transferring to greenhouse. The transmission rate by both aphid vectors Aulacorthum matsumuraeanum Hori and Macrosiphum euphorbiae Thom. was 10 to 20per cent when the aphids were tested individually, indicating that both species were inefficient as the vector as compared with M. persicae.
In the present paper, the actions of root-lesion nematodes, Pratylenchus spp., responses to Fusarium spp. in the soil were observed. (1) When the colony of Fusarium spp. was inoculated into soil infested with P. penetrans homogeneously, the nematode distributions varied ununiformly, and nematodes accumulated within the soil block (Sample A) which existed about the fungus colony; the most extreme occurred when F. oxysporum was inoculated. Ratio of nematodes recovered from Sample A increased 69.2% compared with 50.0% in check 144 hours after inoculation. When F. oxysporum f. lycopersici or F. roseum f. cerealis was inoculated, the accumulations of nematode in Sample A were lower than when F. oxysporum was present. When the colony of Fusarium sp. was inoculated into soil infested with P. coffeae, the nematode distributions varied similarly as in the former results, and the ratio of nematodes recovered from Sample A increased 73.0%. (2) When the culture filtrate of Fusarium spp. was inoculated into soil infested with P. penetrans, the nematode distributions varied ununiformly, and the accumulations of nematode occurred in the soil block (Sample A') which existed about the culture filtrate of F. oxysporum or F. roseum f. cerealis. Ratio of nematodes recovered from Sample A' increased 68.3% to F. oxysporum and 62.0% to F. roseum f. cerealis 144 hours after inoculation. (3) When the colony of Fusarium spp. and the suspension of P. penetrans were inoculated in each different position of sterilized soil simultaneously, the nematodes responsed to existing fungus and the actions were the most extreme when F. oxysporum was used. Ratio of nematodes recovered from the soil block (Sample B") which existed about the colony of F. oxysporum increased 35.7% compared with 16.3% in check 144 hours after inoculation. The actions of nematode to F. roseum f. cerealis were milder than those to F. oxysporum, and the ratio of nematodes recovered from Sample B" indicated 25.8%. When Fusarium sp. and P. coffeae were inoculated into sterilized soil as formerly described, the actions of nematode to Fusarium sp, were extreme and the ratio of nematodes recovered from Sample B" increased 36.1% compared with 15.2% in check. (4) When the culture filtrate of Fusarium spp. and the suspension of P. penetrans were inoculated in each different position of sterilized soil simultaneously, the actions of nematode to Fusarium spp. showed the same tendency as when fungus colony was inoculated, but they were milder generally.
This paper deals with Fusarium solani f. robiniae n. f. [Hypomyces solani f. robiniae n. f.], one of the causal fusaria of the twig blight of Robinia pseudoacacia. This fungus was hermaphroditic and compatibility-heterothallic, and was independent from forms of F. solani in the mating relationship. However, the fertilization occurred between this fungus and F. solani derived from the decaying bark of Populus spp. suggesting that these two fungi are identical. According to the results of cross-inoculations between this fungus and various forms of Fusarium solani, this fungus was pathogenic to its own host, the twig of Robinia pseudoacacia, but not pathogenic to the squash seedling, the bean seedling, the pea seedling, the potato stem, the Morus twig and the Xanthoxylum twig, though mildly pathogenic to the potato tuber and the sweet potato sprout. On the other hand all the other forms of F. solani tested were not pathogenic to Robinia pseudoacacia. From these results the authors proposed a new form for this fungus as follows. Fusarium solani Mart. emend. Snyd. et Hans. f. robiniae Matuo et Sakurai n. f. [Hypomyces solani Rke. et Berth. emend. Snyd. et Hans. f. robiniae Matuo et Sakural n. f.] Hab. in vivis Robiniae pseudoacaciae, cetera ut in typo9). The type culture is deposited in Lab. Phytopath. & Mycol., Fac. Text. Sci., Shinshu Univ., Ueda, Japan, which was isolated from the twig of Robinia pseudoacacia suffered from blight disease.
By cutting the basal part of an infected rice leaf and immersing the cut end in a dilute solution of basic fuchsin for 1 to 2 days, the latent lesions of bacterial leaf blight which were invisible before staining were clearly separated from the stained healthy parts of the infected leaves. The absorption of stain was somewhat influenced by the age of the rice leaf. The entire rice plant also may be stained to demonstrate the diseased area.
A sheath rot disease of rice plant in Indonesia was found to be caused by a strain of Erwinia carotovora. Symptoms produced by this bacterium were similar to those caused by Pseudomonas oryzicola in Hungary and Japan. The results of bacteriological properties and pathogenicity tests indicated that P. oryzicola is rather close to P. marginalis.
White clover mosaic virus (WCMV) was isolated from Ladino white clover showing mottling in Morioka. In the host range study, the legumes Astragalis sinicus, Canavallia ensiformis, Crotalaria spectabilis, Lathyrus odoratus, Phaseolus vulgaris, Pisum sativum, Trifolium hybridum, T. incarnatum, T. pratense, T. subterraneum, Vicia faba, V. villosa, V. sativa, Vigna sesquipedalis and V. sinensis were systemically infected. Local infection was obtained in the legumes Dolichos lablab, Glycine max, Medicago sativa, Lupinus leteus, Phaseolus angularis and P. radiatus, the non leguminous species Datura stramonium, Nicotiana rustica, N. sylvestris, Petunia hybrida, Physalis floridana, Citrullus vulgaris, Cucumis sativus, Ipomoea purpurea and Antirrhium majus. The virus was not transmitted to Nicotiana tobacum, N. glutinosa, Beta vulgaris, Chenopodium amaranticola, Spinacea oleracea and Gomphrena globosa. Test with Cuscuta sojagena indicated that dodder transmission occurs on rare occasions, if it occurs. In insect transmission experiment with Acyrthosiphon pisum, Aphis cravora and Myzus persicae, no transmission was obtained. It seemed that the virus was not transmitted through seed. The thermal inactivation point of the virus laid between 70-75°C and the dilution end point between 1:105 and 1:106. In the aging test, the virus was still active after 60 days, but not after 90 days at 25°C, while it withstood storage for 91 days at room temperature. In the study of electron microscope, the occurrence of flexible rods, about 450mμ in length, was observed, and the mass of the virus particles was evident by the ultra-thin sections was observed. Corner inclusion bodies were observed in the infected cells. Precipitation reaction between the virus isolated in Japan and the antiserum against Pratt's isolate was positive. The virus was found occurring naturally on red clover as well as on Ladino white clover. It is supposed on the basis of host range, symptomatology, transmission, physical properties, morphology of the particles and serological reaction that the virus belongs to the group of white clover mosaic virus that has been reported in several countries.
It has been generally thought that teleutospores of wheat leaf rust (Puccinia recondita Rob. et Desm. f. sp. tritici (Erikss.)) are not formed on young wheat seedlings, but only on adult plants in place of uredospores. While the authors collected a number of uredosorial samples of wheat leaf rust from various parts of Japan and cultured them at a green-house with the study on physiologic specialization of this fungus, one isolate named P 130 (physiologic race 37 B) was found to from teleutospores on the first leaves of young seedlings of wheat. With this as a clue, the authors inoculated to the first leaf of young seedlings of many wheat varieties, including the standard differential hosts to identify physiologic races, at about 1.5 leaf stage, with many fungus isolates belonging to the main races which prevail in Japan, and observed teleutospore formation. The isolate P 130 had a greater ability to form teleutospores on young wheat seedings than many other isolates containing some isolates belonging to race 37 B. It formed teleutosori on many varieties of wheat until twenty days after inoculation, and other isolates also formed teleutosori on some varieties until twenty-five days after inoculation, except races 1 A and 1 B which never formed a uredinial pustule on almost all tested varieties. Contrary to popular belief, most of the leaf rust fungi found in Japan, form teleutospores on the first leaf of young wheat seedlings rather easily. The degree of the teleutospore formation is not related with physiologic races of the fungus, but varies remarkably according to fungus isolates and wheat varieties. The difficulty of teleutospore formation on young wheat seedlings, therefore, seems to be due to the combination of fungus isolate and wheat variety. Teleutosori hardly formed on highly resistant varieties, but easily on the varieties which showed moderate resistance, especially, X-type reaction rather than highly susceptible varieties. Teleutospore formation on young seedlings was divided into seven types. Most commonly, uredosorial ring formed secondarily as a concentric circle around the normal uredosori originated from the first infection, and was replaced by teleutosori which was formed under the uredosori. The teleutosori were formed, therefore, as a intermittent or a continuous ring. Generally, they were not covered with epidermis different from those on adult wheat plants, and the teleutospores were rather short with round tops. They could germinate soon after their formation, as they do on adult plants.