Pseudomonas fluorescens PfG32R, which was shown to be able to suppress the occurrence of bacterial wilt of tomato (BWT), conserves the regions homologous to hrpRS and hrpF of P. syringae pv. phaseolicola and also to hrpC and hrpD of P. s. pv. tabaci but at lower degree. Infiltration of PfG32R into leaves of tobacco or of bean at a high concentration (10⁸cfu/ml) was shown to increase the specific activity of phenylalanine ammonia lyase (PAL) in these plants. Furthermore, when PfG32R was inoculated into leaves of tobacco or of bean with a low bacterial concentration, the level of population increased in the first day from 2×10³ to 1.8×10⁴cfu/leaf disk and it was maintained at a slightly lower level thereafter. This population level was higher comparing to the case of inoculation of plant-unrelated bacterium (Escherichia coli MV118), though it was slightly lower than the level of population in the cases of inoculation of plant pathogenic bacteria, P. s. pv. glycinea and P. solanacearum.

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The factors related to suppression of leaf blast disease with the mixture of the rice cultivar Sasanishiki and its isogenic lines were analyzed. The leaf blast disease severity in the mixture of the compatible and incompatible lines of Sasanishiki was less than in the compatible mixture. The blast disease severity in the mixture, where the plants were infected by an inoculated plant with virulent and avirulent isolates of blast fungus, was less than in the mixture having an inoculated plant with a virulent blast isolate. An induced resistance mechanism operated to depress the leaf blast disease in the multiline of Sasanishiki.

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Fifteen field populations of Plasmodiophora brassicae Woronin (Williams' races 1, 4, and 9) from seven prefectures in Japan were compared by banding patterns of isozymes and soluble proteins from resting spores. When 20 enzymes were examined by electrophoresis on cellulose acetate membrane, 15 enzymes showed activity with acceptable resolution of bands and 11 of them were polymorphic, and seven electrophoretic phenotypes were detected among 15 populations. The population YAYH (Williams' race 9) from Yamaguchi Pref. had the unique banding patterns of 6-phosphogluconate dehydrogenase, hexokinase, alkaline phosphatase, and phosphoglucomutase. When soluble proteins of these populations were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the population YAYH had five unique bands. Cluster analysis of isozymes and soluble proteins revealed two clusters between the population YAYH and other 14 populations (Williams' races 4 and 1) in dendrograms. These results indicate that a part of populations is easily distinguishable from other populations by isozyme and soluble protein analyses. However, pathogenic and nonpathogenic populations to clubroot resistant cultivars of Chinese cabbages of Japan were undistinguishable by these analyses.

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Field isolates and laboratory mutants of Botrytis cinerea, which were collected from different regions in Japan, were crossed in various combinations to produce the sexual stage in vitro. Out of 239 isolates of B. cinerea used in this study, 77 isolates produced numerous and well-developed sclerotia on MGA plates at 12°C in the dark for about 4 weeks. The sclerotia of the 77 isolates were fertilized by conidia of 90 isolates as spermatizing parents, which formed numerous conidia on PSA plates. Out of 77×90 crosses among these isolates, apothecia with ascospores were produced from sclerotia in only 5 crosses. In these crosses, dissimilarity of host plants and/or geographical isolation were noted between both parent isolates.

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Abnormal fruit disorders of Japanese pear cultivars, Niitaka and Yoshino, have been found in Japan since the 1980s. The characteristic symptoms consist of dimpling of mature fruit surface. A viroid was detected in association with this disorder. Healthy Japanese pear trees of cvs. Niitaka and Yoshino were back-inoculated with this viroid and fruit disorders subsequently occurred on these fruits. This viroid is similar in its properties to apple scar skin viroid (ASSVd). When healthy Japanese pear trees of cvs. Niitaka and Yoshino were inoculated with ASSVd, the same symptoms occurred on these fruits. Two primer pairs for RT-PCR amplification of ASSVd RNA were designed from the nucleotide sequence of ASSVd. RT-PCR produced cDNA products of the predicted size for ASSVd using electrophoretically purified viroid samples. Current shoots and dormant shoots were evaluated to be more useful for the detection of this viroid by RT-PCR with a simple extraction method. Amplified cDNA fragments were ligated to pCR^TM II plasmid, and the cDNA inserts were sequenced. The sequence differs from the nucleotide sequence of ASSVd reported by Hashimoto and Koganezawa at only three sites: one nucleotide is deleted, one nucleotide is inserted and one nucleotide is mutated. Therefore the causal agent of this disease is ASSVd. We propose to call this new disease Japanese pear fruit dimple (JPFD). ASSVd was not transmitted from ASSVd-infected Japanese pear trees to pear seedlings by the direct knife-cut method.

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In 1981-1990, Rhizoctonia oryzae which causes bordered sheath spot on rice plants was isolated from lesions on the plants in the paddy fields in T and N districts close to Nagoya City. Classification of these field isolates was conducted on the basis of hyphal anastomosis reaction in pairing test between isolates. Consequent isolates groups (strain) were surveyed in terms of their distribution and Pathogenicity on rice plants. In T district, 11 and 14 strains were found in a field, TO, (no. of plots surveyed: 35) and 18 neighboring ones (no. of plots surveyed per field: 6-8), respectively. Two strains among 11 in TO field were detected to distribute in 6 neighboring fields during survey. Other 2 strains, one from TO field and another one from neighboring field, were found intermittently for 3-4 out of 5-7 years to distribute in one third to about half of the total fields surveyed. These common strains in the same year were maximally 130-140m distant, each other, to conduce to outbreaks of the bordered sheath spot. In another N district, 1 strain among 9 within a field, NE, (do.: 40) was also found in a neighboring field (do: 6-8) 2 years later. In inoculation of heading stage rice plants with one representative isolate belonging to each strain, both ratios of disease severity and diseased culm of plural year-isolated strains in fields were significantly higher than those of 1-year-isolated strains. The latter strains, however, contained some ones showing higher ratios of the disease severity and diseased culm.

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We collected three cabbage plants infected with Peronospora parasitica in Kagawa, two broccoli plants in Mie and one broccoli plant in Tottori. Five single spore isolates from each sample were prepared, and the host range of thirty single spore isolates in total was examined. Test plants used for the host range tests were Brassica oleracea (eighteen cultivars of cauliflower, cabbage and broccoli), B. campestris (eight cultivars of Pak-choi, mizuna, rape, Chinese cabbage and turnip), B. juncea (one cultivar of leaf mustard), B. napus (one cultivar of rutabaga) and Raphanus sativus (two cultivars of Japanese radish). In all the test plants, cotyledons with hypocotyl were used for the inoculation tests. All the B. oleracea plants except two cultivars of cabbage were highly susceptible to all the tested isolates, and it is considered that this is a host species of the fungus. B. napus was moderately susceptible, and suggested to be a possible host species. B. campestris, B. juncea and R. sativus were resistant, and considered to be non-host species. Therefore, all the isolates were considered to belong to the same strain of the fungus and the strain to be specific to B. oleracea and possibly to B. napus. Among B. oleracea plants, two cultivars of cabbage cv. Golden Best and cv. YR-Sawamidori were resistant. Difference in pathogenicity was not found among the tested single spore isolates.

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An isolate of barley mild mosaic virus (BaMMV-Kor) obtained from Iri, Korea-was characterized and compared with three BaMMV strains, BaMMV-Nal and BaMMV-Kal from Japan and BaMMV-M from Germany. Mechanical inoculation experiments showed that BaMMV-Kor was similar to BaMMV-Nal, but differed from BaMMV-Kal and BaMMV-M, in its pathogenicity towards Japanese barley cultivars. However, BaMMV-Kor differed from BaMMV-Nal, as well as from BaMMV-Kal and BaMMV-M, in that it infected most of the Korean naked barley cultivars tested. BaMMV-Kor was distinguished from three other BaMMV strains by ELISA. The sequence of the 3'-terminal 2500 nucleotides [excluding the poly (A) tail] of RNA 1 of BaMMV-Kor was determined to start within a long open reading frame coding for a part of the NIb polymerase (468 amino acids) and the entire capsid protein (251 amino acids), which is followed by a non-coding region (NCR) of 342 nucleotides. The capsid protein of BaMMV-Kor shows higher amino acid sequence homology with BaMMV-Nal (97.2%) than with BaMMV-Kal (92.0%). Likewise, in the 3' NCRs, BaMMV-Kor shows higher nucleotide sequence homology with BaMMV-Nal (96.5%) than with BaMMV-Kal (92.1%). These results indicate that BaMMV-Kor is a new strain of BaMMV, which is closely related to BaMMV-Nal, but differs both biologically and serologically from the Japanese and German strains.

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Single spore isolates of a downy mildew fungus (Peronospora parasitica) on Chinese cabbage (Brassica campestris (pekinensis group)), turnip (B. campestris (rapifera group)) and Japanese radish (Raphanus sativus (daikon group)) plants were obtained from naturally diseased plants in fields. Several single spore isolates from each sample were prepared and the host range of fifty single spore isolates in total was examined. Test plants for inoculations were as follows: twenty-one cultivars of Brassica campestris, one cultivar of B. juncea, five cultivars of B. oleracea, one cultivar of B. napus and two cultivars of Raphanus sativus. In case of inoculations with most of the single spore isolates of P. parasitica from Chinese cabbage and turnip, most of the B. campestris, B. napus cultivars and some B. oleracea cultivars were susceptible, but B. juncea plant was tolerant, although host reaction varied. R. sativus cultivars were resistant to all of the isolates. In case of inoculations with P. parasitica from R. sativus, most of the R. sativus, B. oleracea and B. napus cultivars were susceptible and their reactions varied. Most of B. campestris and B. juncea cultivars were resistant to all the isolates. Therefore, populations of downy mildew fungus occurring on B. campestris and R. sativus plants in fields corresponds to complementary sets of isolates with variable parasitisms, suggesting that physiologic races may exist in downy mildew of B. campestris.

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Factors influencing the occurrence of post-harvest diseases of tulip bulbs caused by Pseudomonas andropogonis and P. gladioli during the storage and distribution were examined. The disease occurrence of the bulbs was promoted by washing in running water or dipping in the insecticide for bulb mite. Thus, following to the increase of the dipping times to the insecticide, the population of P. gladioli in the bulbs increased and the disease increased. The pathogen populations in the bulbs decreased to remove the debris of the bulb scales and roots before washing. The disease development in the bulbs was influenced by several factors such as wounding, wetness, and temperature other than the pathogen density during storage.

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In 1992, diseased flowers of cosmos (Cosmos bipinnatus) were found in Kanagawa Prefecture, Japan. Small water-soaked lesions occurred first on flowers and flower buds. These lesions then enlarged and turned light brown. Diseased flowers and flower buds eventually fell off. The fungus produced fusiform conidia on the PDA medium, 11-14×2.8-3.5μm in size. From those results, the fungus was identified as Colletotrichum acutatum Simmonds ex Simmonds. It has been newly added as a pathogen causing anthracnose on cosmos.

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In October 1994, sprouting inhibition of anemone (Anemone coronaria L.) tuber was found at Tsu city. One species of Rhizopus was isolated from the affected tuber. The morphological characteristics and optimum temperature of mycelial growth of the fungus closely fit the C.M.I. descriptions of Rhizopus oryzae Went et Prinsen Geerligs. The pathogenicity of this isolate to anemone tubers was confirmed and the disease was named tuber rot. This is the first report of tuber rot of anemone caused by R. oryzae in Japan.

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