During the course of the epidemiological survey of virus diseases of tobacco plants, a new strain of potato virus Y (PVY) was isolated from Burley tobaccos.
PVY was fairly prevalent in Burley tobacco and was isolated from 25 out of 40 collected samples. Most of the isolates were considered as ordinary strain. Two isolates (A-1 and A-2) caused yellow spots or yellow ring spots and sometimes necrotic brown or white small spots on systemically infected leaves of White Burley and some of domestic tobaccos. On Bright Yellow tobacco it caused veinbanding symptoms same as those of ordinary strain.
Pepper (Capsicum annuum, cultivar Takanotsume) showed necrotic lesions on inoculated leaves, and also on systemically infected leaves by the infection of all these PVY isolates. It may be useful for differential and quantitative assay host of PVY.
Thermal inactivation point of crude sap of tobacco leaves infected with A-1 isolate was 60-65°C (10min.), dilution end point 1:10⁴ and longevily in vitro 5-6 days at 25°C. Cross protection between the ordinary strain as the first virus and A-1 isolate as the second virus was complete. No protection was observed against tobacco etch virus (Riverside strain) used as the second virus. Antiserum prepared by the injection of purified A-1 isolate to rabbits with adjuvant has positive reactions to the ordinary strain but the titer was lower than that of homogeneous antiserum-antigen reactions. Electron microscopy of the new strain showed fibrous particles with about 700mμ in length.
A-1 isolate resembles tobacco yellow spotted streak strain (Tomaru and Hidaka, 1954) which was isolated from Bright Yellow tobacco in Japan, but different from each other in symptoms on tobacco cultivars and in properties of virus sap. On the symptoms in White Burley tobacco, it resembles one of the isolates in Brazil (Silberschmidt et al, 1954), but the identity is not clear. A-1 isolate may belong to the group of necrotic strain of PVY.

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The longevity of conidia of Pseudoperonospora cubensis had been studied by Iwata, one of the authors, in 1948. In the present experiment it was further studied, especially in connection with the influence of sun light. The results are as follows:
(1) From the results of the germination and inoculation tests, using about 70-100 thousand conidia, it was found that some conidia could survive for 20-45 days of preservation in darkness at 5-7°C and 17°C, although the percentage of survived conidia decreased as the days of preservation became longer (Table 1). No significant difference in the longevity of conidia was observed between at 5-7°C and at 17°C of preservation, although the germination percentage of conidia preserved at 17°C was more or less higher than that at 5-7°C (Table 1). The longevity of conidia preserved at 24, 27, or 30°C was smaller than that at 5-7 or 17°C, but some conidia could survive for five days at these temperatures (Table 2).
(2) Influence of sun light on the longevity of conidia was tested repeatedly on fine days in August 1956 and in May 1957 on the roof of the National Institute of Agricaltural Sciences, Tokyo, using an apparatus shown in Fig. 1 to eliminate the rise of temperature by sun light. The results showed that sun light had no influence on the longevity of conidia (Tables 3 and 4).
(3) The conidia were exposed to a Mazda fluorescent lamp FL20E, which is 270mμ in the shortest wave length and 310mμ in an energy peak (Fig. 2). The percentage of conidial germination decreased with irradiation of more than 3 hours at the distance of 30cm (Fig. 4). Such effect could not be observed when the wave length less than 290mμ was cut out by use of some filters (Fig. 3 and Table 5). From these results it is sup posed that sun light has no influence on the longevity of conidia of this fungus in natural conditions, because the shortest wave length of sun light which can reach on earth, is believed to be about 300mμ.

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In the previous papers (1962, 1966, 1967) the author emphasized the importance of overwintered mycelia in rootstocks as the primary infection source of hop downy mildew and also the possibility that the infection during the previous season may give rise to the main cause of such overwintered mycelia. If the autumn infection is the main source of overwintered mycelia which are the main cause of primary basal spikes in the spring, the autmn foliar spray with effective fungicides may prevent the occurrence of basal spikes in the following spring.
The above mentioned fact was confirmed to some extent by the results of experiments at Furusato Hop Research Laboratory, Sapporo Breweries Ltd. Accordingly, field-tests in the hop grower garden were conducted as large-scale trials based on the previous results. Field-tests for the effect of autumn foliar spray of fungicides on the control of basal spikes were performed in three places, A, B and C; A being located in lowland location, while B and C in high land locations in Nagano Prefecture. The same results were reproduced in the field tests. These facts suggest that the spraying of fungicides after the harvest of cones was important from viewpoint of eradication of the primary infection and indicate that the autumn foliar spray was effective for the reduction of primary basal spikes in the following spring.

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The tomato strain of TMV dealt with herein is chracterized by its producing local lesions but no systemic infection on certain varieties of N. tabacum (Bright Yellow etc.), and also by its higher affinity to tomato plant as compared with the TMV ordinary strain. When the tomato strain and the ordinary strain of TMV were inoculated to seven principal tobacco varieties cultivated in Japan, the tomato strain produced only local lesions on all the varieties, while the ordinary strain produced only systemic mosaic symptoms.
In a survey to see to what extent cigarettes may carry TMV, all of the sixteen Japanese brands (320 lots) tested were found to contain TMV. Strains of the TMV isolates were tested on several test plants. All isolates from eleven brands were only the ordinary strain, while both ordinary and tomato strains were isolated from five of the brands…Hilite, Hope, Kohaku, Izumi and MF.
The tomato strain of TMV is found at a high rate in tomato plants in the field, but is contained in a low percentage in cigarettes manufactured in Japan. This suggests that cigarettes may not be an important source of TMV for tomato crops in Japan.

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The present paper deals with studies on the nucleus of fusion body produced on glucose solution by uredospores of Puccinia coronata Corda, Uromyces alopecuri Seym. and U. durus Dietel, and also nucleus of infection structures of the former 2 species produced on peeled epidermis of host plants and artificial media. The majority of uredospores and germ tubes have two nuclei, and the others only one. Appressorium, substomatal vesicle and infection hypha (no longer than about 200μ), on the other hand, have two to four, two to eight, two to ten nuclei, respectively. The division of nucleus on germination begins at appressorium, and it continues at substomatal vesicle and infection hypha too. In the septated infection hypha, although it is rare, one cell has two nuclei. Organs closely resembling to substomatal vesicle and infection hypha in morphology, which are produced on the outer side of peeled epidermis or artificial media, are the same in nucleus behavior with the respective structures produced just inside the stoma of peeled epidermis. Fusion body usually has two nuclei. The portion where it fuses each other, however, becomes multinuclear because of the nucleus migration out of the original fusion body.

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The effect of root-dipping, banding, and spraying with antiviral substances such as blasticidin S (BcS), ohyamycin (OM), polyoxin A (PO A), and thiouracil (2-TU), upon systemic and local infections of tomato seedlings inoculated with tobacco mosaic virus (TMV) and/or potato virus X (PVX) was studied. A preinoculation root-dipping plus postinoculation banding and spraying reduced the percentage of infection, prolonged the incubation period, and decreased the virus concentration in roots. OM showed the most distinct virus-inhibition, but the root elongation as well as shoot growth was inhibited by OM of 100ppm. BcS of 0.5-1.0ppm and 2-TU of 25-50ppm reduced the severity of symptoms and decreased the virus concentration without apparent toxicities to the plants. Methods for reducing the phytotoxicity caused by these chemicals were tested. It was found that manganese ion, when mixed with BcS or OM, reduced the toxicity due to the antibiotics, especially as judged by a recovery from the retarded root growth. Manganese did not affect so much the virus-inhibition by BcS.

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Present investigation was undertaken to evaluate the controlling effect of Pentachlorobenzyl alcohol (PCBA) on rice blast in relation to characteristics of this compound.
PCBA showed marked protective effects on rice blast in the pot tests in greenhouse. Spraying of PCBA at 30ppm gave good controlling effect equally to that of Hg-20ppm of Phenylmercuric acetate (PMA) as a blast control agent. In field, however, treatment of PCBA at 500ppm was necessary to give good control equally, and more superior to PMA. This compound didn't have therapeutic effect as Blasticidin S did.
Possibility of penetration of PCBA into rice plant and showing indirect controlling function against rice blast as well as its direct was suggested.
In order to control the neck rot, treatment of PCBA about heading time showed the best control, and that of PCBA even a month before heading gave good controlling effect equally to PMA because of good durability.

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Pentachlorobenzyl alcohol (PCBA) is one of the most effective fungicides for the control of rice blast. When blast-infected rice seedlings on a nursery bed outdoors were sprayed with PCBA at 1000μg/ml, spore scattering from the infected seedlings was markedly inhibited from 2nd to 10th day after the spraying. Sporulation on lesions of the sprayed leaves was greatly suppressed during this period. When the leaves, on which PCBA had been sprayed, were detached and incubated at 28°C in a moist chamber, spores were produced as well as on leaves from unsprayed seedlings. The same result was obtained with the test using rice seedlings grown and inoculated under greenhouse conditions. On the contrary, phenylmercuric acetate (PMA, Hg-30 or Hg-20μg/ml) and blasticidin-S (Bc-S, 20 or 10μg/ml) inhibited the sporulation both on leaves of growing plants and on detached leaves. When these three compounds were sprayed on mycelial mats grown on a agar medium in petri dishes, PCBA did not inhibit the sporulation, whereas PMA and Bc-S, each at 40μg/ml, inhibited the sporulation by about 100 per cent. These results clearly indicate that sporulation-inhibiting effect of PCBA is not caused by the direct contact of the compound with the fungus but is caused by an interaction between the compound and the growing rice plant.

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This paper deals with the identification of a virus which was isolated from a mosaic radish plant in Omagari, Akita Prefecture, in Octobar, 1960.
The virus was purified from systemically infected radish leaves (subvariety Kameido) by the following procedure: treatment at 50-53°C for 10min. →repeated shaking with 20% chloroform, salting-out by 0.4 saturated ammonium sulfate, and cycles of differential centrifuging (80, 000G, 60min. and 10, 000G, 10min.) →density gradient centrifugation in 20-50 (or 20-60)% sucrose at 35, 000rpm for 120-150min. (two distinct opalescent bands in the middle) →cycles of differential centrifuging→dialysis against water.
In inoculation tests, the lower band showed a high infectivity, the upper band showed only little infectivity, although the inoculated preparations were far from being a complete separation. Both bands contained particles of similar size and shape, when examined under electronmicroscope after being fixed in 1% formalin and stained with 1% phosphotungstic acid. The particles are spherical and about 25-30mμ in diameter. There were very little "empty" particles in both preparations. The purified preparation showed a maximum UV absorption at 258-260mμ, the absorption curve being that of typical nucleoprotein with 260/280=1.57, and max/min=1.34-1.37. Thermal inactivation point was 65°C (10min. treatment of crude juice), while there was considerable loss of infectivity by treatment at 60°C for 10min.
The virus was readily transmitted by sap-inoculation. The virus was transmitted by the striped flea beetle (Phyllotreta striolata), but not by cabbage stink bug (Eurydama rugosa), two species of aphids (Myzus persicae and Lipaphis pseudobrassicae). There was no transmission through seeds of radish plant, nor through soil.
Various plants were mechanically inoculated with sap from infected radish plants, carborundum being applied to the leaves before inoculation. Many cruciferous plants were found to be susceptible to the virus. The symptoms on infected radish plants were characteristic enation (cf. fig. 3), mosaic, necrosis, and distortion of leaves. Turnip produced necrotic local lesions, and also developed systemic mosaic. Cabbage and cauliflower showed faint susceptibility. Globe amaranth (Gomphrena globosa) produced chloroticspots on the inoculated leaves 7-10 days after inoculation, and rarely developed topnecrosis. Spinach produced chlorotic-spots on the inoculated leaves, and also developed top-necrosis. Petunia was proved to be symptomless carrier, the virus being localized in the inoculated leaves. Chenopodium amaranticolor and C. album produced necrotic local lesions. The following plants were not susceptible: tobacco (Bright Yellow, Xanthi, White Burley), Nicotiana glutinosa, tomato, pepper, kidney bean, cowpea, broad bean, garden pea, cucumber, pumpkin, Chrysanthemum coronarium, morning-glory, beet, rape, Datura stramonium, and Physalis floridana.
To produce antiserum, rabbits were given three muscular injections at intervals of 20 days, of a partially purified virus preparation homogenized with an equal volume of Freund's complete adjuvant. The antiserum obtained had a titer of 1: 5, 000 in the precipitation reaction, the antiserum also reacted with crude juice from diseased radish leaves or with purified virus preparations in agar-gel double diffusion. As the antiserum was produced by using a partially purified virus preparation, crude juice from diseased radish leaves produced non specific as well as specific zones.

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The wilting of rice seedlings appeared at high rate when inoculated at the four leaf stage in the nursery by immersed in bacterial suspension (10⁵ cells/ml) for 16 hours. Most of the lower leaves of wilted seedlings showed ordinary yellow blight symptom and the sixth leaves wilted, whereas the fifth leaves did not show any symptoms.
Histological study revealed that the primary infection occurred only at the hydathode of the lower leaves which were already developed at the time of inoculation, and that the wilting of the upper leaves was due to the vessel embolisms caused by the secondary colonization of those infecting bacteria. The reason why the fifth leaf was not wilted, was that the vessels of this leaf are connected with those of the third leaf where bacterial multiplication was insufficient to induce the wilting. In general, the vessels of the even-numbered leaves did not connect with those of the uneven-numbered leaves. So far as this study, no direct invasion of the bacteria through the roots and the basal parts of the stems was found.
In several cases, the rupture of the infected vessels and bacterial exudation to the intercellar spaces of the parenchyma were observed. The vessels were always ruptured from the inside of the vessels and the infection of the healthy vessels by those exudated bacteria was never recognized.

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Rishitin has been found in tuber tissue of R₁-variety of potato plant infected by an incompatible race of Phytophthora infestans. It seems to be qualified as phytoalexin in broad sense. Rishitin like substances were extracted from tubers of the interspecific varieties (Solanum tuberosum×S. demissum) containing one of the other late-blight resistance genes R₂, R₃, R₄ and common variety (Solanum tuberosum) containing the gene r, and identified as rishitin itself. Thus each of r-, R_1-, R_2-, R_3- and R_4- varieties can produce rishitin in response to infection by an incompatible race of Phytophthora infestans.

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Sap transmissible viruses were isolated from peach var. Nakayamakinto and sour cherry var. Montmorency provisionally laveled isolate-1 and -2.
When buds from Nakayamakinto were used to infect the seeedlings of Prunus species, they induced necrotic ringspot in Mazzard, no symptom in mahaleb, top necrosis of young shoots in flowering cherry var. Magofugen and necrosis and gummosis in var. Shirofugen. Isolate-1 caused chlorotic ringspot and top necrosis in cucumber, chlorotic ringspot on inoculated leaves but not infected systemically in squash, vein necrosis on inoculated leaves and necrotic stem streak in asparagus bean and local chlorotic spot and mottle in Chenopodium amaranticolor. This isolate had a thermal inactivation point of 50-55°C, a dilution end point between 1/100 and 1/500 and longevity was 7-10 hours.
In the case that Montmorency was used for inoculum to seedlings of Prunus species it caused dwarf in mahaleb, necrosis and gummosis in Shirofugen and no symptom in Mazzard and Magofugen. When isolate-2 was used for inoculum, cucumber reacted with mild chlorotic spot on inoculated cotyledons and with mosaic and marformation on young leaves. Squash, tobacco and zinnia were systemically infected with isolate-2 and produced bright yellow vein banding and mosaic on squash and chlorotic ring or mottle on tobacco and zinnia. The thermal inactivation point of isolate-2 was 45-50°C, dilution end point was between 1/50 and 1/100 and longevity was 4-5 hours.
On the basis of these host ranges, symptomatology and physical properties isolate-1 was identified as peach necrotic ringspot virus (NRSV) and isolate-2 was identified as prune dwarf virus (PDV).

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In 1960 the author and his co-worker³⁾ reported an exocortis-like disorder of Satsuma orange trees in Japan. Later, the author carried out the phloroglucinol-HCl color test suggested by Childs^{1, 2)}, but was not successful in proving the disorder to be real exocortis.
In 1963, Dr. W.P. Bitters visited Okitsu Horticultural Research Station and noticed exocortislike symtoms on several varieties of citrus growing at the station. The author conducted the color test with those varieties. The cross sections of the affected bark tissue from trifoliata rootstock were treated with phloroglucinol-HCl reagent (1g phloroglucinol in 100ml. of 70% ethanol and HCl) and examined under microscope. This time, phloem cells, especially the medullary ray cells, stained brick red in color identical to the results of Childs. Since then, citrus exocortis has been considered to be present in Japan⁴⁾.
Citrus varieties that have shown symptoms as described above, are as follows: Temple orange (C. reticulata Blanco hyb.), Everblooming and Eureka lemon (C. limon (L.) Burn. f.), Ruby blood orange (C. sinensis (L.) Osb.), Duncan and Marsh grapefruit (C. paradisi Macf.), and some others. Most of these varieties were believed to be symptomless carriers of exocortis virus. They were imported from the United States, and then grafted on trifoliata rootstocks. Some of the grafted plants were planted in the pots for conservation and others were planted in the field. All affected trees are extremely stunted and produce abnormally small fruit. The fruits of affected. Temple orange trees especially, are very small in size, ripen earlier, have thin and soft rind, and are much more like mandarin than sweet orange fruits.
In spite of the fact that over 90 persent of all citsus trees in commercial groves are grafted on Poncirus trifoliata rootstock in Japan, exocortis virus has not been distributed heretofore. It is believed that Satsuma orange, the most popular variety in Japan, is rather resistant against exocotris virus.

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