A method was devised to assay sporangia and zoospore production of Pythium aphanidermatum quantitatively. One-day old 4-mm mycelial disc from PDA culture was placed centrally on a 2% water agar plate in a Petri dish, and flooded with 4ml of an incubation solution. With this method, sporangium formation and zoospore discharge were more stimulated by Petri's salt solution than Wills's salt solution, soil extract or distilled water as incubation solution. Sporangia and zoospore discharge were more abundant at 30C than at 25 or 20C.

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A method to estimate the yield loss by rice sheath blight disease caused by Rhizoctonia solani Kühn was investigated with ratio of the height of the lesions to the plant height and percentage of the affected hills. Whole disease incidence (D) at the maturing stage could be represented as product of disease incidence of affected hill estimated by ratio of the height of the uppermost lesions to the plant height (X) and percentage of affected hills (A) because it was calculated as
D=(1.62X-32.4)A/100.
On the other hand, the loss of fully ripened kernels has been estimated to be 8.5g per 3.3m² for each additional 1% disease incidence, from which the following equation was derived (L represents yield loss in kg per 10 ares).
L=(41.31X-826.2)A/1000.
The yield loss observed in paddy fields in 1976 to 1980 was in accord with that estimated by the formula.

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Host range and distribution of Pythium myriotylum and unidentified Pythium sp. (Pythium sp. A) which cause the monoculture injury of bean and soybean plants in Hokkaido Prefectural Kitami Agricultural Experiment Station were investigated. Both P. myriotylum and Pythium sp. A were pathogenic to bean, soybean and sugar beet plants among seven rotation crops. They were pathogenic to pea plants as well as bean and soybean plants. The former was pathogenic to adzuki bean plants. P. myriotylum and Pythium sp. A were infrequently isolated from the stunted bean roots in twenty fields and from soils of twenty-four fields of various crops in Hokkaido by indirect method using rye seedlings. These results suggest the host range and distribution of P. myriotylum and Pythium sp. A are limited.

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Mature ascospores of the pear scab fungus Venturia nashicola were produced when mycelial suspensions of two compatible isolates were mixed on the culture media employed and incubated at 5C in the dark for about six months. The inheritance of resistance to thiophanate-methyl, benomyl and MBC was demonstrated experimentally using a technique developed for the production of ascospores. Progeny segregation of the cross between the resistant isolate and the sensitive one fitted a 1:1 ratio, indicating that resistance is under control of a major gene. Additional crosses among resistant isolates suggest the involvement of multiple major genes for different degrees of resistance.

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Relation of soil moisture to the development of angular leaf spot of cucumber was investigated. Cucumber plants grown in the pots were inoculated with Pseudomonas syringae pv. lachrymans 4 days affter the soil moisture of the pots was regulated in three grades, high, middle and low. When soil moisture was kept high, very severe and typical symptoms appeared on the inoculated leaves. On the other hand, when soil moisture was kept low, minute and fewer lesions developed on the inoculated leaves. These minute lesions failed to enlarge thereafter. It was clear that soil moisture was very important condition for infection of the pathogen and development of the disease. When cucumber plants cultivated in glass houses were inoculated with the bacteria, similar results were obtained. The results showed that the higher the soil moisture the greater the extent of disease development. This is consistent with the results of pot experiments. These results show that abundant water in the soil favors the development of angular leaf spot of cucumber.

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Multiplication and distribution of cucumber mosaic virus during the development of systemic infection in tobacco plants (Nicotiana tabacum cv. Xanthi) inoculated to the middle leaf were investigated by the use of fluorescent antibody technique. After the virus multiplied in the inoculated leaf, the virus antigen was first detected in the upper stem and leaves, and later in the lower stem and roots. In the early stage of a long distance movement of the virus, the virus antigen was first observed in separate areas along the phloem. This mode of virus movement differed from that in the parenchyma tissue, in which the virus moved from cell to cell, suggesting that the virus move a long distance through sieve tubes. Thereafter the virus progressively spread from the infection site in the phloem to surrounding tissues and caused the systemic infection. In the upper leaves, the appearance of symptoms such as veinclearing and yellowing followed the distribution of virus antigen in the tissues. After the virus antigen had distributed throughout all the tissues in a certain part of the plant, it gradually decreased.

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Virus particles were not detected in the apical meristem of floral bud and its adjacent tissue in petunia plants infected with TMV. No virus particles were observed in the anther until pollen became differentiated, but thereafter virus multiplied abundantly in anther wall cells. At this stage, however, no virus particles were detected in pollen. At the stage of embryo sac formation, there were no virus particles in the ovule, indicating that the embryo sac differentiated from the virus-free ovule tissue. At flowering time, virus multiplied abundantly in tissues of the stigma and style, whereas in pollen tubes elongating into these organs, no virus particles were observed. Virus particles became detectable in an ovule tissue 4 days after flowering and thereafter in the integument of ovule or the seed coat, but embryo and endosperm appeared to remain virus-free. The virus in the seed coat lost its infectivity as the seed matured. The results obtained in these experiments are consistent with the previous observation that tobacco mosaic virus can not be seed-transmitted in petunia.

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Seven anastomosis groups, AG-1∼AG-6 and AG-BI of Rhizoctonia solani Kühn [Thanatephorus cucumeris (Frank) Donk] are known in Japan. While grouping of R. solani mainly isolated from Japanese radish fields, it was found that 107 isolates composing a single anastomosis group did not anastomose with isolates of any known AG of R. solani. These isolates were obtained from the seedlings of Japanese radish, and the flax or buckwheat stems buried as a bait in the field soil. These isolates were obtained from Nara, Shiga, Tokushima and Kagawa Prefecture located in south-west part of Japan. The isolates were brown or dark brown colony with aerial hyphae and sclerotia, but without clear zonation. Optimum temperature for growth was 28-35C and the linear growth was 25.5-27.0mm/24hr on PDA. The width of mature main hyphae was 7.80-8.27μm and the number of nuclei per cell was 3-11 (mean 5.6). The fungus was thiamine autotrophic. The pathogenicity to seedlings of Japanese radish, bean, cucumber, tomato, barley and rice was slight or negligible. Five, out of 20 tested isolates, formed the white and flake hymenia as solitary islands on the soil surface. Metabasidia were barrel-shaped, short clavate or cylindrical, 11.0-27.5×6.5-11.0μm. Sterigmata were horn-shaped, 5.0-18.0μm in length and (1-) 4 per metabasidium. Basidiospores were obovate to oblong-ellipsoid, hyaline, smooth, with an apiculus, 6.5-13.0×4.0-8.5μm. These morphological characters of the perfect stage show that the new AG is identified as T. cucumeris and we proposed to designate this group as AG-7 of R. solani.

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Forty isolates of Xanthomonas campestris pv. oryzae collected from naturally infected rices in various areas of West Java in Indonesia were evaluated for their virulence to differential varieties of Japan and IRRI. Of 40 isolates in Indonesia, 36 were virulent to Kinmaze, Kogyoku, and Te-tep but avirulent to Wase Aikoku 3 and Java 14. Of 40 isolates of X. campestris pv. oryzae tested, 25 were judged to belong to group A which was identical with the Philippine bacterial group III in terms of virulence. Groups B and C had 6 and 2 isolates, respectively, which were identical with the Philippine bacterial groups I and IV. Two isolates belonging to group I showed a similar virulence to the Japanese bacterial group V and one isolate in group F was apparently similar to the Japanese bacterial group III. Majority of the isolates tested were virulent to IR20 which had a dominant resistance gene, Xa-4, which was same as that of IR36. Therefore, severe outbreak of the disease on IR36 in Indonesia is probably due to occurrence of race which is same as the Philippine bacterial group III. Twenty isolates from Bangladesh were also evaluated for their virulence patterns to the differential varieties. Based on the reaction patterns of the 10 differential varieties of Japan and IRRI, 4 isolates fell under the same bacterial group that was virulent to Kinmaze, Kogyoku, IR8, IR20, IR1545-339, DV85, and Cas 209 but avirulent to Te-tep, Wase Aikoku 3, and Java 14. Similarly, 2 isolates were found to belong to another group that was virulent to Kinmaze, IR8, IR1545-339, DV85, and Cas 209. The virulence patterns of the 2 groups were different from those of any other groups so far reported. The other Bangladesh isolates showed intermediate reactions to differential varieties.

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To clarify the relationship between the amount of anti blast substances, momilactones, in rice leaves and the degree of horizontal resistance to rice blast disease, the quantitative estimation of these substances in leaves of several cultivars which are different in their resistance was conducted by GLC. The authentic momilactone A showed Rt 26.8min and momilactone B-TMS showed Rt 21.1min on OV-17 at 213C and N₂ flow rate 45ml/min. While, momilactone A showed Rt 16.4min and momilactone B-TMS showed Rt 22.1min on OV-101 at 188C and N₂ 45ml/min. These results were quite different from the data of the original report of Cartwright et al. The peaks of momilactones A and B-TMS were analyzed by GC-MS and identified. No momilactones were detected in the extracts from the healthy and blast-infected rice leaves of several cultivars. Although eight-times higher concentration compared with that of the original report was subjected to GLC, momilactones could not detect. These results indicate that the amount of momilactones in infected leaves may be quite lower than the amount reported originally.

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The activities and the electrophoretic patterns of ribonuclease (RNase) in leaves of Nicotiana glutinosa plant after mechanical injury, various chemical treatments and/or tobacco mosaic virus (TMV)-inoculation were investigated. The enzyme activity increased and reached a maximum 16hr after mechanical injury. When the injured leaves were inoculated with TMV, the infectivity also showed a maximum value 16hr after mechanical injury. TMV-inoculation induced an increase in the enzyme activity, but the effect was dependent on the inoculum concentration.
The enzyme was separated into two isozymes, M and F, by polyacrylamide gel electrophoresis. Mechanical injury and TMV-inoculation of the leaves led to an increase of the activity of M and F isozyme, respectively.
Bentonite or sodium dextran sulfate inhibited M isozyme activity, while yeast RNA or eosine Y increased F isozyme activity. However, these chemicals inhibited TMV-infectivity.
When the plants were kept at 35C after TMV-inoculation, F isozyme activity was not detected, but a new isozyme band appeared. However, when the same plants were transfered to an incubator maintained at the lower temperature, 21C, the new band was not detected, but F isozyme appeared again.
The significance of these results was discussed with respect to a possible role of RNase in the infection of TMV.

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Streptomycin (SM) resistance detected in Pseudomonas syringae pv. lachrymans was conjugally transmissible to Pseudomonas aeruginosa carrying 36 megadalton (mdal)-RP4 of incompatibility group Pl by mixing culture method. Such transmission of SM resistance was not seen when P. aeruginosa which did not harbor the RP4 was used as the recipient. Transmitted SM resistance of P. aeruginosa was further transmissible to Escherichia coli by conjugation. Agarose gel electrophoretic analysis of plasmid DNA from the transconjugant P. aeruginosa showed a single plasmid DNA of 43.5mdal, which was capable of transforming both P. aeruginosa and E. coil into SM-, Kanamycin (KM)-, Tetracycline (TC)- and Ampicillin (APC)-resistant. From these results, it was suggested that the transfer of SM resistance from P. s. pv. lachrymans to P. aeruginosa and E. coil might be mediated by the 43.5 mdal-plasmid, and that 43.5 mdal-plasmid might be a recombinant plasmid of 7.5 mdal-fragment of SM-resistant gene from chromosome of P. s. pv. lachrymans and 36 mdal-RP4.

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To establish a simple and practical method for preservation of turnip mosaic virus (TuMV), the effect of some additives was evaluated in connection with different preservation methods. (1) When an equal volume of glycerol was added to suspension of purified TuMV in 10mM potassium phosphate buffer (P.B.) pH 7.0, the high infectivity was maintained for the period longer than 48 months under liquid conditon at -20C. (2) The infectivity of purified TuMV suspended in 10mM P.B. pH 7.0 and crude extract from the infected turnip leaves in 50mM P.B. pH 7.0 decreased gradually under frozen condition at -20C. The infectivity, however, was maintained at high level for long period by the addition of glycerol, sucrose or peptone. At -70C, the infectivity was maintained for longperiod without any additives. (3) By freeze-drying, the infectivity of TuMV in purified preparation decreased markedly, whereas that of crude extract from infected turnip leaves did not decrease. The virus aggregation was considered to be one of the mechanism of decrement of infectivity. The addition of peptone, sucrose or lactose prohibited the aggregation. To obtain the results of protective effect of additives in freeze-drying preservation as quick as possible, the preparations were preserved at higher temperature of 25C and 65C. At 25C, glycine and peptone showed protective effect, while at 65C, only peptone was effective. Glycine was effective for crude extract, while it was ineffective for the purified preparation. Freeze-dried TuMV was considerably stable at 4C and it was quite stable at a temperature lower than -20C, regardless of the kind of additives.

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In 1979, a disease of sickle hare's ear (Bupleurum falcatum L.), characterized by the symptoms of yellows, stunting of the plants, and sometimes witches' broom, was observed in Sakai Town, Fukui Prefecture in Japan. Electron microscopic studies revealed the presence of a large number of pleomorphic mycoplasma-like organisms (MLOs) in the sieve tubes of diseased plants collected from the field, whereas no MLOs were found in the control plants. Of the two leafhoppers, Nephotettix cincticeps Uhler and Macrosteles orientalis Virbaste tested, only M. orientalis was found to transmit the disease. The host range of the disease was tested by allowing infective leafhopper vectors to feed on 117 species of plants belonging to 31 families. Among these, 62 species of plants belonging 21 families was infected, including spinach, turnip, radish, Chinese cabbage, eggplant, Nicotiana glutinosa, onion, welsh onion, lettuce, garland chrysanthemum, carrot, parsley, water dropwort, Japanese hone wort, white gourd, pea, broad bean, white clover, pumpkin and sesame. Out of the experimentally infected species of plant MLOs were recovered from 52 species belonging to 20 families by back inoculation to Japanese hone wort seedlings.

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The clones of the same anastomosis group of Rhizoctonia solani Kühn in the fields of white potatoes, sugar beets, and rice plants were investigated. R. solani was isolated from diseased potato tubers in 3 fields, from infested soils in 10 sugar beet fields, and from diseased culms of rice plants in a paddy field. The most isolates from potato tubers, sugar beet field soils, and rice culms were AG-3, AG-2-2, and AG-1, respectively. Reactions of anastomosed hyphae among the isolates of each group were observed on water agar. The isolates which fused perfectly without death of fused cells (S reaction) were determined to be the same clone, and the isolates which showed death of fused cells (K reaction) were determined to be distinct clones. In potatoes, the most AG-3 isolates from the same tuber showed S reaction. The most isolates from individual tubers in the same field and all isolates from separate fields showed K reaction, In sugar beets, the most AG-2-2 isolates from the same soil sample showed S reaction and the most isolates from separate soil samples in the same field showed K reaction. The all isolates from separate fields, even in the same district, showed K reaction. In rice plants, the most AG-1 isolates from several lesions on one culm showed S reaction. K reaction increased between the isolates from neighbour culms. The most isolates from distant culms showed K reaction. There were 41 clones in this paddy field of 11 ares. In the paddy field, although the distribution of one clone was usually limited, a few clones distributed widely in the field. These results indicate that one field is occupied by a specific anastomosis group pathogenic to the crop growing in the field, that there are many clones of pathogen in one field, and that the distribution of one clone is limited within only small area in the field.

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We deviced a sliced-sheath inoculation method for continuous observation of leaf sheath cells infected with Pyricularia oryzae Cavara. By this method, the aspects of intracellular hyphal growth in the same tissues were observed successively without sectioning of tissues at various times after inoculation. The growth of infection hyphae in sliced-sheath cells was less than that in non-sliced-sheath cells at 32-40hr after inoculation. It might be due to the physiological changes of sheath cells resulted by slicing tissues. The method proposed here seems to be suitable for study of rice-Pyricularia oryzae interaction.

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The favorable substances contained in oatmeal for sporulation of rice blast fungus, Pyricularia oryzae Cavara, were successively extracted from milled oatmeal with petroleum ether, deionized water, 0.9% sodium chloride, 70% ethanol and 0.01N HCl (pH 3-4). Number of conidia decreased remarkably on the medium prepared from the residue left after 70% ethanol extraction. It seemed that one of the favorable substances for sporulation of this fungus existed in oatmeal was prolamin, which was contained abundantly in oatmeal and extracted specifically with 70% ethanol.

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