Due to the similarity in the external symptoms and environmental conditions for the disease development of tomato Fusarium wilt (race J3) and tomato brown root rot (Pyrenochaeta lycopersici), it is often difficult for tomato growers to distinguish them from each other without phytopathological tests. The interspecific hybrids between Lycopersicon esculentum×L. hirsutum, commonly named KNVF or KVF were tested for the possibility of using them as differential plants to diagnose the diseases. Two tomato rootstocks (KNVF and KVF) were found to be resistant to single or multiple inoculation with the two pathogens (Fusarium and Pyrenochaeta) at almost the same level. These results indicate that it is difficult to use the rootstocks as differential plants. Roots of KNVF on which Fukuju 2, a Japanese tomato variety, was grafted and planted in soil infested with the causal fungus of tomato Fusarium wilt (race J3), remained clean and showed only mild lesions suggesting resistance to the infection with the fungus. On the other hand, the roots of non-grafted Fukuju 2 become severely infected and the tops of the plant wilted. From the result, the grafting of a horticultural variety on KNVF was found to be useful to control tomato Fusarium wilt (race J3) in practice.

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Primary inoculation of an incompatible bacterium, Pseudomonas syringae pv. tabaci, to the loquat leaves, induced the growth inhibition of compatible strain B of P. syringae pv. eriobotryae inoculated 3 days after against to the same leaves. The growth inhibition of the parasitic bacterium was not observed when the sequence of inoculation was carryed in reverse order. Inoculated loquat leaves with the incompatible strain C of the pathogen or P. syringae pv. tabaci produced a phytoalexin (aucuparin) as early as 24hr post inoculation and its activity increased thereafter. Bacterial growth in the leaves was inhibited with the accumlation of aucuparin in the leaves. In contrast, when loquat leaves were inoculated with the compatible strain B, the bacterial population in the leaves increased gradually until 14 days when the lesion development was observed. Aucuparin activity was not detected before lesion development, but it increased rapidly thereafter and later reached a high level. A possible role of aucuparin in loquat leaves against P. syringae pv. eriobotryae was discussed in relation to the mechanism of disease resistance.

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Radish yellow edge virus (RYEV) was purified from infected Japanese radish (Raphanus sativus L.) by CsCl equilibrium density gradient centrifugation. Virus particles banded with a buoyant density of about 1.37g/cm³ in CsCl. Purified RYEV preparations showed UV absorption spectrum characteristic of a nucleoprotein with A_max/A_min and A₂₆₀/A₂₈₀ ratios of about 1.10 and 1.39, respectively. Proteins from purified RYEV preparations, electrophoresed in SDS-polyacrylamide gels, migrated as two species with mol. wt. of about 63, 000 and 61, 000. RYEV nucleic acid was judged to be double-stranded ribonucleic acid (dsRNA) from its resistance to RNase in high ionic strength conditions and from its reaction with an antiserum to poly (I): poly (C). In polyacrylamide gel electrophoresis, RYEV dsRNA was fractionated into three major classes with mol. wt. of approximately 1.30, 1.25, 1.21×10⁶ and two minor ones of 1.14, 1.09×10⁶. RYEV was not related serologically to turnip crinkle, turnip rosette, turnip mosaic and cucumber mosaic viruses which infect crucifers or to ten seed-borne viruses which resemble RYEV in particle morphology and biological aspects. It is highly likely that RYEV and several other seed-borne dsRNA viruses constitute a new group of plant viruses.

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Proteinaceous components which agglutinated unwashed bacterial cells of Xanthomonas campestris pv. citri and its extracellular polysaccharides (EPS), but not washed cells and unwashed EPS-nonproducing mutant cells, were isolated from citrus leaves of Citrus unshiu, C. natsudaidai and C. reticulata, forming fibrous materials. The agglutinin was prepared by extraction with HCl-acidic water (pH 4.0) from homogenate of the leaves followed by precipitation with 50%-saturated ammonium sulfate. This agglutinin was heat and protease labile, insensitive to various salts except higher concentration than 100mM, and was inhibited at pH higher than 6.0. The Similar agglutination of unwashed cells and EPS of other xanthomonads (X. campestris pv. campestris and X. campestris pv. phaseoli), but not that of pseudomonads and erwiniae, was also demonstrated. Of 18 sugars tested, only D-glucosamine (25mM) showed a potential activity to inhibit the agglutination of X. campestris pv. citri, but not that of other xanthomonads.

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Ryegrass mottle virus (RMotV), a previously undescribed mechanically transmissible virus, was obtained from field infected Italian ryegrass (Lolium multiflorum) and cocksfoot (Dactylis glomerata) in Japan. The virus causes mottling and necrotic symptoms in leaves and readily infects wheat (Triticum aestivum), barley (Hordeum vulgare), oat (Avena sativa), rye (Secale cereale), Italian ryegrass and Italian millet (Setaria italica). Cocksfoot, chewing fescue (Festuca rubra) and perennial ryegrass (Lolium perenne) were less readily infected. The virus particle is isometric and ca. 28nm in diameter. The particles have a sedimentation coefficient (S_{20, w}) of 108 S and a buoyant density of 1.366g/ml in CsCl. They contain a single RNA component of mol. wt ca. 1.5×10⁶, representing about 23% of the particle weight, a major protein of mol. wt 26, 000 and possibly two minor proteins of 17, 500 and 16, 500. In double-diffusion tests, antiserum to RMotV reacted weakly with cocksfoot mottle virus and phleum mottle virus, apparently not to a common antigen. No relationship to RMotV was detected with antisera to cocksfoot mild mosaic, phleum mottle, cocksfoot mottle and cynosurus mottle viruses. RMotV is considered to be a newly discovered virus and a member of the phleum mottle virus group. Its present cryptogram is R/1:1.5/23:S/S:S/*.

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During cooler seasons, a new bacterial disease of onion plants has recently be found in Tokai and Kinki areas in Japan. A small water-soaked lesions on the leaf blades appeared as an initial symptom, and the symptom developed into streak along the leaf veins, resulting from the enlargement and conjugation of the lesions. The streaks progressed to a part of leaf sheaths, and eventually leaf sheath and scale bulb tissues decayed completely with the disease development.
Thirty-one bacterial isolates obtained from the infected plants were divided into 2 genera from their diagnostic charaters. Twenty isolates of them were identified as Erwinia rhapontici (Millard 1924) Burkholder 1948 on the basis of their bacteriological properties. On the other hand, 11 isolates were also determined as Pseudomonas marginalis pv. marginalis (Brown 1918) Stevens 1925. These are the first description of bacteria which cause the diseases on onion plants.
These isolates possessed an ability to affect onion tissues by needle-prick and carborundum inoculations. The symptoms caused by E. rhapontici were hardly distinguished from those of P. marginalis pv. marginalis, although they were scarecely different in discoloration of soft-rotted host tissues. In addition, it was observed that most of naturally infected plants were attacked by these 2 pathogenic bacteria at the same time. From the reasons mentioned above, we propose to use a single common name “soft rot of onion” for the both bacterial diseases, hereafter.

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Following to the previous studies on bacterial canker of Japanese apricot (Prunus mume Sieb. et Zucc.), 31 pathogens isolated from shoots and fruits of Japanese apricot were compared their bacteriological characters with Pseudomonas syringae pv. syringae NCPPB 524 and P. syringae pv. morsprunorum NCPPB 330. All the isolates were short rod-shaped, aerobic, Gram-negative and motile by one to several polar flagella. They metabolized glucose oxidatively and showed catalase activity, and produced levan. They showed negative reaction on VP-MR tests, oxidase and arginine dihydrolase activities, and did not produce hydrogen sulfide or indole. They produced acid from arabinose, xylose, mannose, fractose, glucose, sucrose, cellobiose, ribose, glycerol, mannitol, sorbitol and inositol, but not from maltose, melezitose, dextrin, galactitol, adonitol, α-methylglucoside or salicin. They were divided into three groups (A, B and C) by the differential tests for distinguishing P. syringae pv. syringae and P. syringae pv. morsprunorum which consist of bacteriological tests such as growth in sucrose broth, longevity on nutrient sucrose agar, liquefaction of gelatin, hydrolysis of aesculin and arbutin, pigment on tyrosine, pigment on King's B and utilization of lactic acid and tartaric acid. Group C bacteria (27 isolates) were characterized to be quite similar to those of pv. morsprunorum in differential tests and pv. morsprunorum NCPPB 330, a check strain. The other two groups bacteria (A and B, 2 isolates respectively) were different from group C in some bacteriological characters. The 31 isolates and the 2 check strains were proved to show virulence to immature green fruits of Japanese pear and overwintered twigs of Japanese apricot, but to be avirulent to lilac leaves. On the basis of bacteriological characters and pathogenicity, group C bacteria were identified as Pseudomonas syringae pv. morsprunorum (Wormald 1931) Young, Dye and Wilkie 1978, and group A and B bacteria as its strain.

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Two filamentous phages of Xanthomonas campestris pv. oryzae, Xf and Xf2, are almost similar in DNA base composition. To investigate the degree of homology between Xf and Xf2 more in detail, the cleavage patterns of their replicative form DNA (RFI-DNA) treated with restriction endonucleases were compared by means of polyacrylamide gel electrophoresis. RFI-DNA was prepared by ethanol-precipitation method from the lysate of phage infected-bacteria. DNAs of Xf-RFI and Xf2-RFI thus obtained had infectivity to X. campestris pv. oryzae and their molecular weights were estimated at 4.5×10⁶ and 4.7×10⁶ daltons, respectively, from their relative mobilities. Both RFI-DNAs were treated with endo R. Hpa II, Hha I, Hind II, Hae III and Alu I to be subjected to the electrophoresis. Since most of the cleavage products of both RFI-DNAs showed remarkable difference in electrophoresis patterns, the phages Xf and Xf2 were considered to be heterogeneous.

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Resistance of tomato agaisnt TMV was examined by using various plant materials, such as callus tissues, protoplasts from callus tissues or leaves, leaf discs, cotyledons and intact leaves of resistant tomato plants carrying Tm-2² gene. TMV multiplication in these materilas was estimated by means of quantitative immunoelectrophoresis using FITC-conjugated antibody. An amount of TMV, after incubation of inoculated callus tissues on solid medium for 6 days, was much higher in callus tissues of susceptible tomato plant than of resistant plants. The difference in these two types of callus tissues was more distinct in the largest pieces of callus tissues than in smaller ones, which were produced when they were inoculated with TMV by shaking. In the smallest pieces of callus tissues, there was no difference between callus tissues prepared from susceptible and resistant plants. In protoplasts, there was no significant difference between resistant and susceptible plants. On the other hand, a significant difference was detected in leaf discs, cotyledons and leaves of both plants. These results indicated that resistance gene, Tm-2², of tomato against TMV functioned effectively in large pieces of callus tissues as well as leaf discs and other intact materials of tomato, but not in protoplasts.

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DNA base sequence homology among isolates within each anastomosis group of Rhizoctonia solani, AG-3, AG-5, AG-7 and AG-BI, was investigated on the basis of DNA-DNA reassociation kinetics to examine their genetic relatedness. DNA homology value of isolates within each anastomosis group ranged from 97.6 to 100% with AG-3 (potato type, IV), from 94.0 to 98.2% with AG-5, from 95.6 to 98.8% with AG-7, and from 91.4 to 100.2% with AG-BI. These results suggested that each of these anastomosis groups is genetically homogenous.

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Two morphologically distinct types of small, spherical virus-like particles (VLPs), tentatively designated as type A and B, were purified from rice plants infected by downy mildew in field. Type A shows a diameter of 30nm with phosphotungstic acid (PTA) staining or 32nm with uranyl acetate (UA) staining, bearing spikes of 4nm on its periphery. Type B has a diameter of 32nm with PTA staining or 35nm with UA staining and no spikes. Purified preparations of type A and B showed an ultraviolet absorption spectrum with maximum at 260nm and minimum at 244nm, indicating their nucleoproteinaceous nature. The A₂₆₀/A₂₈₀ ratios of type A and B were 1.44 and 1.60, respectively. Antisera prepared against type A and B individually did not react with heterologous antigens. Out of 46 samples collected from the fields throughout Miyagi Prefecture, 11 samples contained both types, 9 samples contained only type A, 21 samples contained only type B and 5 samples contained none. Healthy rice plants collected near the two diseased fields contained neither type A nor B.

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Xanthomonas campestris pv. oryzae and X. campestris pv. oryzicola, the pathogens incompatible and compatible to parenchymatous tissue of rice leaves, respectively, were infiltrated into intercellular spaces of the tissue to investigate host-parasite interactions. Both bacteria induced secondary water-soaking at the infiltrated sites by the 3rd day and yellowish or brownish lesions restricted in size developed by the 7th day after infiltration. X. campestris pv. oryzicola caused typical symptom of the translucent and yellowish streaks later on whereas X. campestris pv. oryzae did not. Ultrastructural changes of the host tissues and parasites were investigated on the 3rd, 7th and 14th days after infiltration. In the specimens infiltrated with X. campestris pv. oryzae, swelled, loosen, and partially peeled host cell walls were frequently observed at the site close to the bacterial cells on the 3rd day after infiltration. The host plasmalemma adjacent to the pathogen was receded from cell wall showing vesiculation and became indistinct. Up to the 7th day after infiltration, the bacteria multiplied in some degree in the intercellular spaces and inside cells of host tissue. Most of them, however, were morphologically abnormal and surrounded by fibrillar material (FM) which appeared to be originated from host cell wall and cytoplasm. On the 14th day after infiltration, the majority of the bacterial cells were surrounded by much amount of granular materials (GM) originated from denatured host cell wall and cytoplasm, showing morphological distortion. On the contrary, X. campestris pv. oryzicola multiplied vigorously with normal shapes in the intercellular spaces and inside cells of the host parenchymatous tissue up to the 14th day after infiltration. Neither FM nor GM appeared in this combination. These facts suggest that FM and GM observed in the rice leaf parenchymatous tissue infiltrated with X. campestris pv. oryzae seemed to be closely related to the defense mechanism of host tissue against the incompatible pathogen.

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Purification of rice ragged stunt virus (RRSV) was improved by using Triton X-100 as a detergent, adding MgCl₂ in suspension buffers and using histidine buffer in the latter step of the procedure. The purified virus particles were about 55nm in diameter and highly infectious to rice seedlings, inoculated via vector insects (Nilaparvata lugens). Ten double stranded ribonucleic acid (RNA) segments with approximately equimolar amounts, including newly found two segments, were found in purified RRSV. A total molecular weight of the RNA was 22.91×10⁶ based on the standards doveloped by Galinski et al.

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Antibacterial substances were produced in the citrus leaves inoculated with Pseudomonas sp. which was known as a bacterium antagonistic to the symptom development of citrus canker. The crude extracts from the leaves inoculated with cell suspension of Pseudomonas sp. (A-ex), or mixture of Pseudomonas sp. and Xanthomonas campestris pv. citri (AX-ex) remarkably inhibited the growth of X. campestris pv. citri, whereas the crude extract from the leaves inoculated with X. campestris pv. citri alone (X-ex) showed week inhibition. Several fractions of A-ex by thin layer chromatography (TLC) on a silica gel plate markedly inhibited the growth of X. campestris pv. citri. From these fractions, two inhibitory substances, CLP-3 and CLP-5, were isolated by TLC with two developing solvent systems. The concentrations of these two substances were extremely high in A-ex and AX-ex, but very low in X-ex. The substances showed higher antibacterial activity against Pseuomonas sp. than X. campestris pv. citri. It suggests that these substances might be phytoalexins. These antibacterial substanes produced by inoculation of Pseudomonas sp. are considered to play some important roles in the mechanisms of the inhibition toward development of citrus canker.

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A virus was isolated from symptomless asparagus plants (Asparagus officinalis) in Hokkaido, Japan. The virus infected 28 plant species belonging to 8 families by sap inoculation. Artificially infected asparagus plants occasionally produced faint, light-green mosaic symptoms on the leaves. The virus was transmitted through seeds of infected plant of asparagus, tobacco, Zinnia elegans and Petunia hybrida, but not by aphids. Thermal inactivation point of the virus was between 55 and 60C, dilution end point between 10^-3 and 2×10^-4 and longevity in vitro was 2-3 days at 20C. Purified virus preparation contained isometric particles with a diameter ranging from 26 to 36nm, and reacted positively with the antisera in immunodiffusion test against asparagus virus II described in the U.S.A.
On the basis of symptomatology, host range, mode of transmission, physical properties, particle morphology and serological relationships, the virus was identified as asparagus virus II.

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Pathological changes of rice sheath tissues caused by Rhizoctonia solani treated with validamycin A (VM-A) was anatomically observed. In sheaths inoculated with mycelial disks after dipping in solutions of 0.63, 1.25, and 2.5ppm VM-A, browning of sheaths and small elliptical spots arose, but no hyphae were observed in the inner space of the sheath. On the other hand, in the lessions formed by inoculation of untreated mycelial disks, abundant hyphae were present in the inner space of the sheaths and the parenchyma cells were severely damaged. Spraying of 10ppm VM-A at 8hr after inoculation of R. solani inhibited the penetration of hyphae into sheath tissues and the browning of sheaths on inoculated part or small elliptical spots were seen on the 4th day. When VM-A was sprayed 16hr after inoculation, hyphae became to be seen in the sheath tissues on the 4th day. Their growth, however, was strikingly inhibited accompanying with little damage of the tissues compared with the lesions formed by the untreated hyphae. The results demonstrate that VM-A is effective against R. solani by both preventing hyphal penetration and retarding its growth.

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Hyphal growth and host responses were investigated in rice leaf-sheaths inoculated with Pyricularia oryzae and other Pyricularia spp. When the sheaths of the nine rice cultivars, having different genes of resistance to P. oryzae, were inoculated with the incompatible race of rice blast fungi, there were large differences in hyphal growth among the cultivars. In the cvs. Kanto 51 and Toride 1, the growth of most intercellular hyphae of the incompatible races was very poor in the values of both the average and highest indices; all invading hyphae were located in the first invaded cells. In the cvs. Ishikari-shiroke and Yashiro-mochi, however, most invading hyphae of the incompatible races developed well into the sheath cells; fungal behaviors and morphological changes of host cells showed almost same tendency as those in the compatible race-cultivar interactions. When non-detached sheaths of those cultivars were inoculated with the incompatible races of P. oryzae, blast lesions similar to susceptible lesion were formed on the surface of leaf-sheath 10 days after inoculation. On the other hand, in case of non-host interactions with non-pathogenic Pyricularia spp., hyphal growth was very poor in all combinations.

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Among the 10 kinds of plant extracts tested, celery extract was the best for chlamydospore formation by Fusarium oxysporum f. sp. niveum. Addition of 0.03M Na₂SO₄ to 2% celery extract greatly increased the number of chlamydospores produced. Light was inhibitory to chlamydospore formation in celery extract plus Na₂SO₄. The medium supported chlamydospore formation by five other formae speciales of Fusarium oxysporum, and two isolates each of Fusarium roseum and Fusarium solani. Chlamydospores of F. oxysporum f. sp. niveum produced in this medium germinated 87 to 98% in 6hr and caused 89 to 100% death of watermelon seedlings.

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The effect of temperature on the inactivation of radish yellows pathogen (Fusarium oxysporum f. sp. raphani) during anaerobic fermentation of radish residues was examined. The debrises of diseased radish roots were anaerobically fermented under the different temperatures, by sealing up in plastic-film bags. Either at varying or constant temperature in the range from 10 to 30C, the higher the temperature, the faster the inactivation of the pathogen progressed. Inactivation of the pathogen occurred obviously with the progress of fermentation.

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A virus was isolated from spinach plants showing rugose symptom in Saitama prefecture. The virus was readily transmitted by sap inoculation and by aphid, but not through seed of spinach. The virus had similar host range to CMV-P, although it did not produce any symptoms on tomato and cucumber. The virus was spherical particles, 30nm in diameter, and was serologically indistinguishable from CMV-P. Electrophoresis of RNA of the virus revealed four component showing minor differences in mobility from the components of CMV-Y and CMV-P. We propose the name of the virus, CMV-SR.

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In 1982, a disease of strawberry plant, showing the symptoms of stunting and witches' broom, was observed in Shizuoka city. Electron microscopy revealed the presence of mycoplasmalike organisms (MLOs) in the sieve tubes of the diseased plants. Macrosteles orientalis, and Macrosteles fascifrons were found to transmit the disease to healthy plants. Of 29 species plants in 14 families, which were inoculated by the infectious M. orientalis, 26 species plants in 12 families were infected with the MLO. The strawberry witches' broom had a wide host range similar to those of sickle hare's ear yellows.

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Rice sheath blight fungus, Rhizoctonia solani (IA), was isolated at the rate of 100% from the mature rice plants having many sheath blight lesions. However, from the diseased samples of sheath blight like lesions, Sclerotium oryzae-sativae was isolated at the rate of 70%. High isolation rate of S. hydrophilum was observed in the plants with many sheath blight lesions, but R. oryzae was detected more often in the plants with sheath blight like lesions. S. hydrophilum and S. oryzae-sativae were frequently isolated from lesions near the basal parts of the plants.

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