A potyvirus isolated from passionfruit hybrid cultivar Ohdama (Passiflora edulis×P. edulis f. flavicarpa) showing systemic mosaic symptoms on the leaves and producing severely malformed and woody fruits, collected in the Amami main island of Kagoshima Prefecture, was identified as passionfruit woodiness virus (PWV). The isolate, designated as PWV-AO, was transmitted by aphids, Myzus persicae, in a non-persistent manner and induced local infection in Chenopodium amaranticolor, C. quinoa, Solanum melongena and Phaseolus vulgaris and systemic infection in Passiflora caerulea, P. foetida and Sesamum indicum by sap inoculation. P. edulis, P. edulis f. flavicarpa and Ohdama could be infected with the virus only by aphid and graft inoculations. Sap from diseased Ohdama was infective to P. vulgaris cv. Sujinashi Edogawa after dilution to 10^-4 but not 10^-5, after heating for 10min at 55°C but not at 60°C, and after 2 days at 25°C but not 3 days. The virus particles were filamentous, 787nm long. In ultrathin sections, pinwheel and scroll inclusions were observed in the cytoplasm of infected Ohdama leaf cells. The virus particles contained a single protein species of MW 35, 000. PWV-AO reacted strongly with an antiserum to a PWV-Brazilian isolate (PWV-B) and weakly with antisera to soybean mosaic virus (SbMV) and watermelon mosaic virus-2 (WMV-2), suggesting that PWV-AO was serologically similar to PWV-B and have a distant serological relationship to SbMV and WMV-2.

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Phenotypically distinct rice dwarf Phytoreovirus (RDV) variants which caused varying degree of stunt symptoms were segregated from three field sources after selective transfers using the insect vector. These variants were serologically identical. After the ninth transfer of a field source RDV-W, an extremely severe variant (RDV-W-M) and a mild variant (RDV-W-L) were isolated. Their structural proteins migrated identically in SDS-polyacrylamide gel electrophoresis (PAGE). Migration pattern of genomic dsRNAs in PAGE was different among the variants. Especially the mobility of genome segment 6 (S6) was different between severe and mild variants isolated from each of the three sources. The amount of viral antigen in plants infected with variants was correlated to their severity in symptomatology. These results may suggest that S6 is involved in efficiency of viral multiplication and symptom severity.

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The complete nucleotide sequence of the RNA genome of bean yellow mosaic potyvirus (BYMV) has been determined. The RNA genome of BYMV is 9532 nucleotides long excluding the poly (A) tract. The RNA contains one open reading frame (ORF) of 9171 nucleotides encoding a large polypeptide of 3056 amino acids with a calculated M_r of 347, 571. Nine putative proteolytic cleavage sites, one by P1 protease, one by HC protease and seven by NIa protease, are identified by comparison with those identified for other sequenced potyviruses. The genetic organization of BYMV genome is proposed to be 5'UTR (190nt)-P1 (33K)/HC-Pro (52K)/P3 (41K)/6K1/CI (71K)/6K2/NIa-VPg (22K)/NIa-Pro (27K)/NIb (59K)/CP (31K)-3'UTR (171nt)-poly (A). Comparing the amino acid sequences of individual BYMV proteins with the corresponding proteins of other potyviruses, the BYMV proteins, excepting P1, have a high or moderate homology.

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Validamycin A (VM-A), the active ingredient of Validacin^®, inhibits fungal growth by inhibiting trehalase activity. Therefore, VM-A was tested against Pseudomonas solanacearum for its efficacy in controlling tomato bacterial wilt. In media containing trehalose as the sole carbohydrate, VM-A at 50μg/ml inhibited growth of P. solanacearum to rates similar to that of the bacteria in media without carbohydrate for seven days after inoculation. VM-A also gave excellent control of tomato bacterial wilt in greenhouse pot tests, when directly injected into plant stems. In field tests, foliar sprays of VM-A at 250μg/ml five days before and two days after inoculation had reduced disease by 47.4% by four weeks after inoculation. In the tomato stem between 0 and 5cm above the soil line, the bacteria population in the non-treated plot reached 3.84×10¹⁰cfu/g fresh weight, whereas that in the VM-A (500μg/ml)-treated plot reached 2.13×10⁹cfu/g fresh weight. Inhibition of bacteria growth by VM-A may delay the appearance of disease symptoms of tomato bacterial wilt.

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Flexuous, filamentous virus particles with a length of 700-800nm were detected in garlic (Allium sativum L.) plants showing mosaic symptoms. The virus was sap-transmissible from garlic plants to seven out of 25 plant species tested, inducing local lesions on Chenopodium murale and Gomphrena globosa and a systemic mosaic on garlic. This virus was transmitted by the eriophyid mite, Aceria tulipae Keifer, but not by aphids. Two polypeptides with M.W. 30kDa and 28.5kDa were detected by SDS-PAGE of the purified virus preparation. The virus exhibited no serological relationships with leek yellow stripe, onion yellow dwarf or garlic latent viruses. No cytoplasmic cylindrical inclusions were observed in infected leaf cells of garlic or C. murale. The 3'-terminal nucleotide sequence of 2518bp was determined. It contained three putative open reading frames (ORFs) for 40kDa, 28kDa (a putative coat protein, CP) and 15kDa polypeptides. The arrangement and amino acid sequences of these ORFs show close similarities with those of shallot virus X and garlic virus (GV)-A, -B, -C and -D. The putative CP of the mite-borne virus has 98% amino acid sequence homology with CP of GV-C, but only 60-67% identity with CPs of four other viruses, indicating the classification of the mite-borne virus and GV-C as the same virus. We propose the name garlic mite-borne mosaic virus (GMbMV) for the virus.

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[in Japanese]

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Flower buds of kiwifruit grown in plastic tunnel were inoculated with Pseudomonas syringae, a causal pathogen of bacterial blossom blight, 6 to 8 times from April to May in 1990 and 1992. Occurrence of the bacterial blossom blight was evaluated in relation to the day required for calyx splitting and flowering as well as the correlation between bud development and disease incidence. Disease incidence was significantly high when the buds were inoculated 10 to 19 days before flowering. Buds at 10 days before calyx splitting resulted in high disease incidence and the average days required from calyx splitting to flowering were 10 days. Disease incidence of early developmental stage (A to D) was higher than the late stage. These results showed that flower buds between 10 and 19 days before flowering was the most susceptible to the bacterial infection, suggesting that P. syringae needs to infect the flower buds before calyx splitting followed by the rapid increase of bacterial density within the buds.

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During the 5 years from 1989 to 1994 (except 1993), calyx splitting and flowering date and occurrence of bacterial blossom blight of kiwifruit were investigated on a total of 89 trees (100 to 200 flower buds per a tree). While the date of calyx splitting negatively correlated with the disease occurrence, a positive correlation was found between disease occurrence and the number of days from calyx splitting to flowering. Although new canes were deliberately infected with Pseudomonas syringae, a causal pathogen of bacterial blossom blight of kiwifruit, flowers on the shoot tips were more resistant to the disease than those on the bottom. No difference was observed in the population density of P. syringae among the flowers on the new canes. These results lead to the conclusion that decrease of disease incidence on new canes might result from the number of days between calyx splitting and flowering, suggesting that the later rate of bud development, the more disease occurrence increased.

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Control of bacterial blossom blight of kiwifruit by treatment of ringing to main trunk were examined. Ringing treatment more than 5mm in width at approximately 25 days before flowering showed a stable effect on the control of the disease. Changes in percentage of water content, shoot length and percentage of flower buds with morning dew were examined by ringing treatment on the main trunks to reveal the mechanism of disease suppression by the treatment. Ringing treatment showed a marked effect on the suppression of bacterial blossom blight caused by Pseudomonas syringae, a causal pathogen of the disease, although no difference was observed in the infection rate. Water content of trees showed no significant effect by the ringing treatment. Ringing treatment effectively suppressed the shoot elongation, and formation of morning dew on the flower buds in comparison with that of the control. However, P. syringae could be detected within the morning dew. Since decrease in the formation of morning dew correlates positively with decrease in shoot length. These results suggested that the reduction in the disease occurrence by ringing treatment partly resulted from the decrease in the amount of morning dew on flower buds.

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Effect to the various meteorological factors on the occurrence of bacterial blossom blight of kiwifruit was statistically analyzed in 9 years from 1987 to 1995. Growth stage of the plant was classified into six stages by 10 days interval from flowering to 60 days before flowering. Meteorological factors used were as follows; temperature (T), maximum temperature (T_max), minimum temperature (T_min), difference in maximum and minimum temperature (DT), relative humidity (RH), minimum relative humidity (RH_min), hour of sunshine (HS), amount of insolation (AI), precipitation (P) and days of rainfall (DR). Flowering stage positively correlated (P<0.05) with disease incidence. Twelve meteorological factors showing correlation coefficient greater than 0.5 were T, T_max, H, P and DR at stage 2, DT, RH, RH_min and AI at stage 3, T_min at stage 4 and T and T_max at stage 5. When these 12 factors were analyzed multiple regression by foreword selection method, five factors were found to have significant probability at least 5% level; P and T_max at stage 2, DT and RH at stage 3 and T at stage 5. R² of the 5 factors was calculated to be 61.2%. These results suggest that account for the occurrence of bacterial blossom blight above 5 factors, especially from 10 to 29 days before flowering.

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In 1994 and 1995, hydrangea phyllody occurred in Tochigi, Shizuoka and Oita Prefectures, Japan. The affected plants (Hydrangea macrophylla and H. serrata) showed phyllody and proliferation of flower organs, as well as stunting and dieback. Electron microscopy revealed the presence of phytoplasmas in the phloem sieve elements of affected sepals and leaves. The phytoplasmas were transmitted to healthy Catharanthus roseus by graft inoculation. Using primers for 16S rDNA by polymerase chain reaction (PCR), DNA fragments of 1.3 and 0.75kbp were amplified in DNA samples extracted from affected hydrangeas but not in those extracted from healthy plants. This is the first report on the occurrence of hydrangea phyllody in Japan.

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In June to September 1995, a new powdery mildew was found on baby's breath (Gypsophila paniculata L.) in Hiroshima and Fukushima, Japan. A white, powdery mycelial colony appeared on the leaves and stems of the plants. Conidia were ellipsoid to cylindric, 31-54×14-22μm, forming singly on conidiophores. Lobed appressoria differentiated on the germ tubes from conidia. Cleistothecia were not found on diseased plants. On the basis of the morphology of conidial stage, the fungus was proposed to be an Oidium sp. of the Erysiphe polygoni type. “Powdery mildew of baby's breath” was proposed for the disease.

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Twenty-five strains of Pseudomonas syringae pv. glycinea were studied for their ability to produce coronatine and symptoms on soybean leaves. Seven strains induced lesions accompanied by halos on soybean leaves after natural and artificial infection, whereas the other strains induced lesions without halos. Five of the seven halo-inducers also produced coronatine on potato tuber tissues, whereas the 18 non-halo inducing strains did not. However, all 25 strains produced coronatine in Woolley's liquid medium. In addition, all twenty-five strains had a pCOR1-like plasmid in size. The cfl region in pCOR1, which is correlated with coronatine production in P. syringae pv. atropurpurea, was also detected in the pCOR1-like plasmids in all 25 strains. These results indicate that P. syringae pv. glycinea essentially has coronatine-producing ability, but its expression in planta may be regulated by a control system.

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