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Kawaguchi A.,Research Institute for Agriculture | Inoue K.,Research Institute for Agriculture | Inoue Y.,Japan National Agriculture and Food Research Organization
Journal of General Plant Pathology | Year: 2014

A suspension of nonpathogenic Xanthomonas campestris (nXc) strain AZ98101 or AZ98106 was sprayed on peach trees in biological control tests against bacterial spot caused by Xanthomonas arboricola pv. pruni. Treatment with each strain reduced the number of leaves with spots. Meta-analysis of the results from seven field trials showed an integrated risk ratio (the ratio of leaf spot incidence on inoculated leaves to incidence on control leaves) of 0.46 by treatment with AZ98101 and 0.54 by AZ98106, indicating that leaf spot incidence was significantly reduced by each strain. Each also significantly reduced the incidence of fruit spot. The risk ratio with AZ98101 was significantly lower than that with AZ98106. The population of AZ98101R-1, a rifampicin-resistant mutant of AZ98101, was 6.3 × 103 CFU/g (fresh mass) on leaves and 8.0 × 103 CFU/g on fruit at 12 days after inoculation, but was undetectable (<102 CFU/g) by 24 days. This is the first report that nXc strains AZ98101 and AZ98106 effectively control bacterial spot on peach. © 2014 The Phytopathological Society of Japan and Springer Japan.


Kawaguchi A.,Research Institute for Agriculture | Inoue K.,Research Institute for Agriculture
Journal of Phytopathology | Year: 2012

Graft unions of nursery stock of grapevine (Vitis vinifera L.) collected Japan yielded non-pathogenic strains of Agrobacterium. On the basis of classic diagnostic tests, a sequence analysis and a previously reported multiplex PCR method, the non-pathogenic strains ARK-1, ARK-2 and ARK-3 were identified as Agrobacterium vitis. Stems of grapevine seedlings were inoculated with both a cell suspension of seven mixed strains of A. vitis (Ti) as a pathogen and one of a new straor A. vitis straVAR03-1, one of the biological control agents against crown gall previously reported, as competitors to assay the suppression of tumour formation caused by the pathogen. a test with a 1:1 cell ratio of pathogen/nonpathogen, strains ARK-1, ARK-2 and ARK-3 reduced the tumour incidence.. particular, straARK-1 was strongest at inhibiting tumour formation this study. StraARK-1 established populations on roots of grapevine tree rootstock and persisted on roots for a year. ARK-1, ARK-2 and ARK-3 did not produce a halo of inhibition against A. vitis (Ti) straon YMA medium. Moreover, straARK-1 did not reduce tumour incidence on the stems of grapevine when ARK-1 was dead or only culture filtrate was used. This result indicates the possibility that these new strains inhibit grapevine crown gall planta by a different mechanism other than VAR03-1. particular, one of the new strains, named ARK-1, was most effective inhibiting tumour formation on grapevine and appears to be a promising new agent to control grapevine crown gall. © 2012 Blackwell Verlag GmbH.


Nagai K.,Research Institute for Agriculture | Hikawa M.,Research Institute for Agriculture
Japanese Journal of Applied Entomology and Zoology | Year: 2012

Black-eyed Susan Rudbeckia hirta L. was evaluated as an insectary plant of a minute pirate bug, Orius sauteri (Poppius). In reinforced greenhouses, we established a treatment plot in which black-eyed Susan growing in planter boxes was arranged along the tomato rows, and a control plot of tomato without black-eyed Susan. O. sauteri and its prey, such as aphids, whiteflies and thrips occurred on the black-eyed Susan from mid-July to late September. On the black-eyed Susan, a relatively high population density of O. sauteri was maintained from mid-August to mid-September even when the population density of the prey was very low. Two species of whitefly, Trialeurodes vaporariorum(Westwood) and Bemisia tabaci(Gennadius) occurred on tomatoes in both plots during the duration of this experiment. The population density of O. sauteri on tomatoes in the treatment plots increased as did that on black-eyed Susan; however, the population density of O. sauteri on tomatoes in the control plot showed no increase throughout the study. The population density of O. sauteri on tomatoes in the treatment plots was significantly higher than that in the control plots(two-factor repeated measures ANOVA, p>0.05). The results indicate that the high density of O. sauteri on tomatoes in the treatment plot is due to immigration of O. sauteri from black-eyed Susan to tomato; however, the difference in the population densities of whiteflies between the two plots was not significant(two-factor repeated measures ANOVA, p>0.05).


Kawaguchi A.,Research Institute for Agriculture
Microbes and Environments | Year: 2013

A nonpathogenic strain of Rhizobium vitis ARK-1 was tested as a biological control agent for grapevine crown gall. When grapevine roots were soaked in a cell suspension of strain ARK-1 before planting in the field, the number of plants with tumors was reduced. The results from seven field trials from 2009 to 2012 were combined in a metaanalysis. The integrated relative risk after treatment with ARK-1 was 0.15 (95% confidence interval: 0.07-0.29, P<0.001), indicating that the disease incidence was significantly reduced by ARK-1. In addition, the results from four field trials from 2007 to 2009 using R. vitis VAR03-1, a previously reported biological control agent for grapevine crown gall, were combined in a meta-analysis. The integrated relative risk after treatment with VAR03-1 was 0.24 (95% confidence interval: 0.11-0.53, P<0.001), indicating the superiority of ARK-1 in inhibiting grapevine crown gall over VAR03-1 under field conditions. ARK-1 did not cause necrosis on grapevine shoot explants. ARK-1 established populations on roots of grapevine tree rootstock and persisted inside roots for two years.


Differences in hrpZ sequences determined by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) were used to investigate the molecular epidemiology of Pseudomonas syringae pv. syringae (PSS) strains that were isolated from diseased barley and wheat plants in Okayama, Japan. PCR-RFLP using HhaI separated PSS strains into two groups (A and B). Although specific PCR-RFLP groups of PSS strains were not always isolated from specific cultivars or seeds produced in a specific area, many strains isolated from barley and wheat belonged to PCR-RFLP groups A and B, respectively. © 2012 The Phytopathological Society of Japan and Springer Japan.


Kawaguchi A.,Research Institute for Agriculture
European Journal of Plant Pathology | Year: 2015

A nonpathogenic strain of Agrobacterium (=Rhizobium) vitis, ARK-1, limits the development of crown gall of grapevine (Vitis vinifera L.). Co-inoculation of grapevine shoots with ARK-1 and the tumorigenic (Ti) strain VAT03-9 at a 1:1 cell ratio resulted in significantly lower expression of the virulence genes virD2 and virE2 of VAT03-9 1 day after inoculation (dai) compared with expression levels when shoots were inoculated only with VAT03-9. In contrast, nonpathogenic A. vitis strain VAR06-30, which does not limit the development of crown gall of grapevine, co-inoculated with VAT03-9 did not affect expression levels of virD2 and virE2 under the same conditions. ARK-1 began to suppress the VAT03-9 population by seven dai, but no such effect was observed with VAR06-30 during the nine dai study period. Thus, the biological control activity of ARK-1 is likely based on the suppression of essential virulence genes. © 2015, Koninklijke Nederlandse Planteziektenkundige Vereniging.


Kawaguchi A.,Research Institute for Agriculture
Journal of General Plant Pathology | Year: 2011

Forty-one strains of Rhizobium vitis, either tumorigenic (Ti) or nonpathogenic, were characterized using multilocus sequence analysis (MLSA) of the partial nucleotide sequences of pyrG, recA, and rpoD. The strains separated into seven clades. Rhizobium vitis (Ti) strains isolated from Japan were divided into five genetic groups (A to E), and nonpathogenic R. vitis strains were divided into two genetic groups (F and G). This result suggests that there are new genetic groups of R. vitis in Japan. Among these groups, members of A and B groups are widely distributed throughout Japan. © 2011 The Phytopathological Society of Japan and Springer.


Kawaguchi A.,Research Institute for Agriculture
Journal of General Plant Pathology | Year: 2014

Bacterial spot, caused by Xanthomonas arboricola pv. pruni, is the most important disease that affects peach production in Okayama Prefecture, Japan. Currently, this disease is managed mainly with copper compounds applied at two stages, before flowering and after harvesting, or with antibiotics applied in May and June. Here we identified the disease risk factors that affect peach at harvest and developed a disease-forecasting model to help growers decide when to apply bactericides. The model was based on parameters for weather data collected for September and October of 2001 through 2012 and for April, May, and June of 2002 through 2013, combined with data on bacterial leaf spot incidence obtained from 28 to 30 fields per year in August from 2001 to 2012 and in May to July from 2002 to 2013. The model, developed using a logistic regression analysis, included the percentage of fields with a bacterial spot incidence (BSI) ≥1 % in mid-August of the previous season and the number of rainy days (≥5 mm/day) during the current June as predictors, and explained 75.0 % of the variability. These results suggest that the previous season’s BSI and weather variables in the present season can be used to predict the risk of bacterial spot. © 2014, The Phytopathological Society of Japan and Springer Japan.


A nonpathogenic strain of Rhizobium (=Agrobacterium) vitis, ARK-1, limited the development of grapevine crown gall. A co-inoculation with ARK-1 and the tumorigenic strain VAT07-1 at a 1:1 cell ratio resulted in a higher population of ARK-1 than VAT07-1 in shoots without tumors, but a significantly lower population of ARK-1 than VAT07-1 in grapevine shoots with tumors. ARK-1 began to significantly suppress the VAT07-1 population 2 d after the inoculation. This result indicated that ARK-1 reduced the pathogen population at the wound site through biological control. Although ARK-1 produced a zone of inhibition against other tumorigenic Rhizobium spp. in in vitro assays, antibiosis depended on the culture medium. ARK-1 did not inhibit the growth of tumorigenic R. radiobacter strain AtC1 in the antibiosis assay, but suppressed the AtC1-induced formation of tumors on grapevine shoots, suggesting that antibiosis by ARK-1 may not be the main mechanism responsible for biological control. © 2014 Microbes Environ. All rights reserved.


Okubo K.,Research Institute for Agriculture
Plant Production Science | Year: 2014

Seed shattering is an important agronomic trait in rice as it directly affects the yield. Manipulation of the degree of shattering will maximize the yield potential. This study was performed to find an indicator for indirect selection to facilitate the selection of medium-shattering habit in japonica rice breeding. The grain shattering pattern and microscopic morphology of the separation zone on pedicels of five japonica rice cultivars with different shattering habits were compared. Almost all grains were separated between the sterile lemma and rudimentary glume in cultivars with medium-shattering, easily-shattering and very easily-shattering habits. On the other hand, approximately 50% of the grains of the cultivar with hardly-shattering habit were torn off at the bent portion of pedicel. A separation pileus was formed on the terminal of the pedicel. The pileuses were most prominent in cultivars with easily-shattering and very easily-shattering habits, while cultivars with a medium-shattering habit had more flat pileuses than prominent pileuses. Additionally, in the cultivar with a hardly-shattering habit all pileuses were flat. Development of fibrous cell walls on the separation pileus varied with degree of shattering habit. The easier the grain shattered, the poorer was the development of fibrous cell walls. These results strongly suggest that the shape of separation pileus and the development of fibrous cell walls are related to the shattering habit in japonica rice. Additionally, it is highly probable that the medium-shattering habit is characterized by the type of shattering that separates between sterile lemma and rudimentary glume with the flat shape of pileus. © 2014 by The Crop Science Society of Japan.

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