Although Xanthomonas oryzae is usually cultured on ring rot medium, this medium is not suitable for counting the viable number of this bacterium because the colony formation rate varies markedly on this medium. From the results of the study on the variation of colony formation rate, it was found to be influenced by composition, concentration, and pH of the medium, incubation temperature, etc. It was also noticed that variety and place of production of potatoes used was the most important factor. Therefore a synthetic medium that provides a high degree of stability and reappearance of colony formation rate was required. This is accomplished by modification of the synthetic medium, originaly formulated by Mukoo and Watanabe, as follows: Na-glutamate 2g, MgCl2⋅6H2O 1g, K2HPO4 0.1g, Fe as EDTA salt 1mg, sucrose 5g, distilled water 1 liter; pH was adjusted to 7.0. Bacterial colonies developed well on this modified synthetic agar medium and the colony formation rate was ca 80% when 50∼200 cells were inoculated. A few precautions are necessary in preparation and use of this medium. The Fe-EDTA solution must be renewed once a week in summer and once a month in winter. When viability counts are estimated on this medium, better results are obtained by addition of 1% of peptone as the colonies on the synthetic medium with peptone appear faster than those on the synthetic medium alone. This modified synthetic medium is suitable for estimating viability counts but is not suitable for stock culture.
1. The isolates of Phytophthora infestans, twenty-seven from potatoes and forty-one from tomatoes, were obtained from different localities of eleven prefectures in Japan. These isolates were used for inoculation upon the seedlings of Irish Cobbler (Danshaku) potato and Ponderosa tomato. All isolates caused severe infection on potato seedings but on tomato caused different severities of infection. According to the relative strength of pathogenicity to tomato seedlings, these isolates were classified into three different groups. ‘Potato-type’ was lowp athogenic, ‘intermediate-type’ was moderately pathogenic and ‘tomato-type’ was highly pathogenic on tomato seedlings. 2. Of the potato isolates, seventeen isolates (60.0%) belonged to potato-type, five (18.5%) to intermediate type and four (14.8%) to tomato-type. Among the tomato isolates twenty-eight (68.3%) were tomato-type and eight (19.5%) were intermediate type. 3. Many potato isolates were collected from Shizuoka and Shimizu cities, in May and June from the year 1959 to 1961. The frequency of three types in these isolates were examined. All of fifty-one isolates collected in 1959 were potato type and thirty isolates in 1960 were identified as intermediate-type (4 isolates) and potato-type (26 isolates). Among one hundred and fifty-two isolates collected in 1961, five were tomato-type, six were intermediate-type and others were potato-type. 4. In serial passage experiments of the potato-type and intermediate-type through tomato foliage, it was found that the intermediate-type had acquired the virulence equivalent to the tomato-type after ten passages, but the potato-type had declined after four passages.
1. The isolates of Phytophthora infestans, fifteen from potatoes and twenty from tomatoes, were tested for pathogenicity to the differential tomato varieties, Ponderosa, West Virginia accession-19 (W.V.-19), 36, 106 and 700. These isolates were classified into four races: 1) potato-type, weakly pathogenic or nonpathogenic to all tomato varieties; 2) tomato race O, pathogenic to Ponderosa and W.V.-19, but weakly pathogenic to W.V.-36, 106 and 700; 3) tomato race 1, pathogenic to Ponderosa, W.V.-19, 36, 106, but weakly pathogenic to W.V.-700; 4) tomato race X, pathogenic to all tomato varieties. 2. Thirty consecutive passages of the tomato race O through foliage of a susceptible variety did not increase its virulence. But ten passages through a resistant variety increased its virulence, showing virulence almost equal to tomato race 1. 3. According to the cross inoculation tests with the potato races and tomato races on the differential varieties for each, it was found that isolates belonging to a single potato race usually comprised several tomato races, and vice versa. There was no relationship in pathogenicity between the tomato and potato races. 4. With respect to the varietal susceptibility of tomatoes, all of eighteen commercial varieties tested were found to be highly susceptible not only to tomato race X but also to tomato race O.
1. This paper presents the results of experiments concerning physiological specializations of Cladosporium fulvum. Fifty-four isolates, obtained from nine prefectures in Japan, were used for race classification using differential tomato varieties as Ponderosa (susceptible), Leaf Mold Resister No. 1 (cf1), Vetomold (cf2) and V-121 (cf3). These isolates were identified as race 0(51 isolates) and race 3(3 isolates), according to Day's system. Furthermore, on the basis of minor differences in pathogenicity, the race 0 were separated into four subraces as race 0(0), 0(1), 0(3) and 0(1·3). 2. Other thirteen resistant varieties than before stated differential ones were inoculated with ten isolates which belonged to above races and subraces, respectively. Stirling Castle showed low resistant reaction to race 0(1) and highly resistant reactions to other races. Another twelve varieties showed highly resistant reactions to all isolates. 3. In few cases, susceptible lesions were found on the matured plants of resistant varieties, i. e., L.M.R. No. 1, Antimold B and V-121. The isolates obtained from L.M.R. No.1 and Antimold B were identified as race 0 and the isolate obtained from V-121 was identified as race 3 which was pathogenic on this variety. 4. Two types, angular and circular, of the lesion of leaf mold can be observed on the tomato leaves. It was found that one variety forms always angular or circular lesions, when inoculated with any races. On the variety which the palisade parenchyma are interrupted by the vein tissues, lesions are angular. The other hand on the varieties which the palisade parenchyma are not interrupted but continue over the veins, lesions are circular.
1. The incubation periods of the rice dwarf virus were investigated both in the insect vectors and rice plants. In the leafhoppers, the shortest incubation period was found to be 8∼12 days and the longest to be 33∼37 days at a constant temperature of 18°C., whereas no insect became infective at 13°C. It appears that the virus does not multiply in the insect body at 13°C. In young rice plants the shortest incubation period was 11 days at 18°C. 2. The ability to transmit the virus seems to vary in leafhoppers captured at different localities, the leafhoppers from Chiba Prefecture having transmitted the virus more readily than those from Shiga and Akita Prefectures. The leafhoppers from Shiga and Akita Prefectures became infective more readily when virus preparations were injected with a glass capillary into their bodies through a puncture made in the abdomen. 3. The virus concentration in the leafhopper was shown to increase most rapidly during a period of 15∼20 days after the virus acquisition. In an infective leafhopper, the virus concentration appears to be almost equal in the cephalothorax and in the abdomen, the extracts from these parts having the same dilution end point, 2×10-4. 4. The virus concentration in the infected rice plant attained its maximum 40 days after inoculation. At this time, extracts from leaves and stems of diseased rice plants were infective at a dilution of 10-3 and those from roots at a dilution of 10-2. Extracts from the yellow-green portions of affected leaves were infective when diluted to 10-4, while those from the green portions were remarkably less infective. 5. The virus was carried in the vectors through 4 serial passages. It was calculated that the quantity of the virus in the starting leafhopper would have undergone a dilution of 10-11 in the last group of the series, if the virus had not multiplied. Since the dilution end-point of the juice from infective insects was 10-4, the author was led to the conclusion that the virus multiplies in the insect vector.
1. When extracts from leaves of diseased rice plants or from viruliferous leafhoppers were centrifuged at 10, 000rpm for 30 minutes the virus was slightly precipitated, but it was completely precipitated by centrifugation at 20, 000rpm for 120 minutes. Partially purified preparations of the virus were secured by two cycles of alternate low and high speed centrifugations. The sedimentation constant of the virus particle in M/30 phosphate buffer was determined to be 405×10-13sec. 2. Nucleic acid extracted from partially purified virus preparations with water saturated phenol and sedimented with NaCl was found to be infective, when injected into the abdomen of non-viruliferous leafhoppers, but the preparations sedimented with ethanol were devoid of infectivity. 3. When rabbits were injected intramuscularly with an emulsion of partially purified antigen in Freund's adjuvant, a high titer antiserum was obtained. 4. The virus could not be cultivated on the chorioallantoic membrane of developing chick embryo.
Ten to eighty percent of the potato plants of variety May Queen were found to show top necrosis when tuber-grafted with virus-X-infected potatoes of eight varieties, but show no reaction when grafted with virus-X-free varieties. Hence the virus which induces top necrosis on May Queen was considered to be closely related to or associated with virus X. Some May Queen plants did not show top necrosis, although the donors were undoubtedly infected with virus X. To confirm this, cores from the same virus-X-infected tuber were grafted to different potatoes of May Queen. The reaction of the test plant varied with individuals. Fortunately, a May Queen plant showing mosaic symptoms, infected with virus X, was found in 1959 at Tsumagoi Potato Foundation Stock Farm, Gunma Prefecture. By using this material, cross protection tests were made. The results showed that the top-necrosis-causing virus was completely antagonistic to X-virus, which originated in May Queen (Tab. 4) Cockerham (1943) identified the virus causing top necrosis on May Queen as virus B, but other workers have considered this virus B to be a strain of X-virus. Bawden (1944) demonstrated that his top-necrosis had incomplete cross-protective reaction with X-virus. It seems that the virus causing top necrosis on May Queen in Japan is a strain of virus X, which may be related to B, but it differs from B in the cross protective activity with virus X.
An attempt was made to eliminate the latent viruses from potato plants of Danshaku variety, which is synonymous with Irish Cobbler and the one most commonly cultivated in Japan. All current stocks of the variety are infected with potato viruses X and S. The tubers were planted in soil under glass, and the apical meristems of their sprouts were excised into pieces less than 0.2mm in length and cultured in Kassanis' medium (1957). When these meristems grew into plantlets about 3∼4cm long, they were transferred directly from culture medium into sterilized soil. Of 158 meristem cultures, only five grew into plantlets, which were proved all to be free from virus X. One plantlet was tested for virus S, and shown to be free. Three of the plantlets survived and produced small tubers.