Tomato yellow leaf curl virus (TYLCV) vectored by the sweetpotato whitefly Bemisia tabaci, is a major threat to tomato production. Recently, some tomato growers cultivate a TYLCV-resistant cultivar for control of TYLCV in Chiba Prefecture. The effect of the Japanese commercial resistant cultivar on TYLCV epidemiology has not been well understood. Therefore, the role of the TYLCV infected resistant tomato cultivar on viral acquisition and transmission by its vector was studied in a tomato grower’s greenhouse. The viral copy number in resistant tomato leaf was 1.4×107-5.6×108 TYLCV DNA copies per 1μg total leaf DNA. In line with the high copy numbers, viral acquisition rate of whiteflies obtained from the greenhouse was 85.7%. Furthermore, these whiteflies transmitted TYLCV to the TYLCV-susceptible cultivar. It is highly probable that the TYLCVresistant tomato cultivar could be the reservoirs for TYLCV.
In a plant growth factory in Tsukuba, Japan, cucumber plants cultivated with spray hydroponics were wilted. The causal agent was identified as Pythium aphanidermatum based on morphological and genetic characters. Cucumber plants grafted onto squash plants as rootstocks escaped wilt in the factory, but were diseased when grafting points were infected by the pathogen. Eight major squash cultivars for rootstock for cucumber bred in Japan were not wilted after zoospores of the pathogen were mixed with the nutrient solution, however seven cucumber cultivars were wilted. Squash rootstocks would be available for suppression of Pythium root rot on hydroponic cucumbers.
Root rot of cucumber occurred on Hahajima in Ogasawara (Bonin) Islands in 2013 and 2014. The causal fungi isolated from the diseased plants were identified as Globisporangium (Pythium) splendens. Inoculation tests confirmed that this fungus was the causal agent of the disease. This is the first record of the disease in Japan.
Rhizoctonia blight of komatsuna (Brassica rapa var. perviridis) occurred in Ibaraki Prefecture on July, 2009.The causal agent was identified as Rhizoctonia solani AG-4 HG-I, and pathogenicity of this pathogen was moreprominent at relatively high temperature condition. We propose that R. solani AG-4 HG-I should be added tothe pathogens of Rhizoctonia blight of komatsuna.
In July 2009, yellowing and irregularly-shaped lesions on the leaves of komatsuna (Brassica rapa var. perviridis) were observed in a plastic greenhouse in Ibaraki Prefecture, Japan. The pathogen was identified as Hyaloperonospora brassicae based on the morphological features of conidiophores and conidia, the sequence of rDNA-ITS region and host range of the pathogen.
Little is known about Fomitiporia torreyae, a pathogen of Japanese pear dwarf. Therefore, we used the polymerase chain reaction (PCR) to develop a method for the specific detection of the pathogen in decayed wood. In the ribosomal DNA internal transcribed spacer (rDNA ITS) region, the degree of sequence homology between F. torreyae and related species was between 84 and 99%. We used the F. torreyae rDNA ITS sequence to design specific primers (FP-f1 and FP-r1) for detection of the pathogen. When the primers were tested with several isolates of F. torreyae and eight other basidiomycetes isolates, we obtained the expected PCR products (356 bp) only from the F. torreyae isolates. We then developed a method for the extraction of mycelial DNA from decayed tissues of infected trees. Samples were grated by using emery paper with a buffer containing 10% PEG and 0.35 M sorbitol, and the resulting DNA samples were used for PCR reactions. The sensitivity of detection was improved by the use of nested PCR reactions. Thus we were able to specifically detect the Japanese pear dwarf pathogen, F. torreyae, in decayed wood by PCR.
Fruit rot of atemoya (Annona × atemoya Hort. & Wester) occurred in Chichijima-island of Tokyo in December 2014. The pathogen isolated from the diseased pod was identified as Colletotrichum theobromicola based on morphological characteristics and molecular analysis of the rDNA-ITS, β-tubulin and actin regions. Inoculation test showed that the fungus was the causal agent of the disease. This is the first report of this disease in Japan.
Cacao pod rot of Theobroma cacao L. occurred in Chichijima-island of Tokyo in 2014. The pathogen isolated from the diseased pod was identified as Colletotrichum tropicale based on morphological characteristics and molecular analyses of the rDNA-ITS, β-tubulin and actin regions. Inoculation test showed that the fungus was the causal agent of the disease. This is the first report of this disease in Japan.
Datura spp. are medical herbs used as raw material in products such as pain-killers. Since September, 2012, we have investigated diseases of the medical herbs in the Tokyo Metropolitan Medicinal Plant Garden and found leaf spots on Datura inoxia and D. metel. On the spots, Alternaria crassa was abundantly observed. In this study we confirmed the pathogenicity of A. crassa to three Datura species (D. stramonium, D. metel and D. inoxia) and proposed the name of leaf spot (Japanese name: rinmon-byo) for the diseases.
Rhizoctonia rot of Chinese foxglove, beach silvertop and common soapwort, and southern blight of sand plantain and heal-all occurred at the Tokyo Metropolitan Medicinal Plant Garden in 2013 and 2014. The causal fungus isolated from each plant of Chinese foxglove, beach silvertop and common soapwort was identified as Rhizoctonia solani, while the fungus from sand plantain and heal-all was identified as Sclerotium rolfsii. The diseases were first reported on the plants in Japan.
In June and July 2013, Southern blight symptoms were observed on St John's wort, Japanese valerian, common verbena, fairy bells and chives in Kodaira, Japan. From each symptom, one fungus was isolated. Koch’s postulates were conducted by inoculating these healthy plants with the isolated fungi and indicated that the isolated fungi have pathogenicity to the plants. Based on detail morphological examination and ITS homology test, the pathogens were identified as Sclerotium rolfsii Saccardo. To our knowledge, this is the first report of S. rolfsii causing this blight on the five plants in Japan.
In 2013, orange hawkweed, pincushion-flower, August-lily, potentilla, astilbe and prostrate speedwell were blighted in flower beds in Saitama, Japan. The pathogens isolated from each diseased plant were identified as Sclerotium rolfsii based on morphological observations and ITS homology test. This is the first report of the diseases in Japan.
Two severe leaf spot diseases were observed on Arabian jasmine and Elaeagnus × ebbingei in Japan. Fungal isolates were obtained from acervuli on these diseased leaves. Based on morphological and ITS sequence data, the isolates were identified as Colletotrichum tropicale on Arabian jasmine and C. siamense on Elaeagnus × ebbingei. This is the first report of Arabian jasmine and Elaeagnus × ebbingei causing Anthracnose in Japan.
Occurrence of second generation larvae and eggs of rice skipper was investigated on purple rice variety Purple rice of NARO Institute of Crop Science (Purple rice) and forage rice cultivar‘Momiroman’, latetransplanted in a paddy field. Number of eggs on leaves of the two varieties did not differ significantly, whereas number of larvae on Purple rice was significantly less than that on‘Momiroman’. Survival rate of newly hatched larvae was investigated by a laboratory rearing experiment using leaves of the two varieties. Half of the larvae on Purple rice leaves had left the leaves within 24 hours, whereas most larvae on‘Momiroman’leaves stayed on the leaves after 24 hours. It is possible that the Purple rice plant is not a suitable food for newly hatched larvae.
Thrips-control ability of the mirid bug Nesidiocoris tenuis (Reuter) was investigated against Thrips tabaci Lindeman on cucumbers grown in greenhouses. In 2013, the cucumbers were transplanted in August, and the bugs were released three times with seven-day intervals at the density of 0.5 bugs per plant. In 2014, the bugs were released four times on the cucumbers transplanted in March in the same manner as in 2013. In both trials, the density of thrips on cucumbers was significantly reduced in the bug-released greenhouse.
In 2008 and 2009, we investigated the species composition of ladybird beetles and their seasonal changes in tea fields of Shizuoka Prefecture, Japan. The ladybird beetles were detected by three methods: yellow sticky traps in the tea canopy, SE traps on the tea canopy and beating the side of the tea canopy. Five tea fields in our research center and commercial fields were investigated. Pest management at these fields included various pesticide and non-pesticide control measures. Eight species of the ladybird were found; Chilocorus kuwanae Silvestri, Pseudoscymnus hareja (Weise), Hyperaspis japonica (Crotch), Harmonia axyridis (Pallas), Scymnus (Pullus) kawamurai (Ohta), Coccinella septempunctata Linnaeus, Propylea japonica (Thunberg), and Phymatosternus lewisii (Crotch). The dominant species were C. kuwanae, P. hareja and H. japonica. These three species are predators of scales, and the others seem to be predators of aphids. The peaks of C. kuwanae occurrence in 2008 were observed at the end of June, the beginning of August and mid-September. The peaks of P. hareja were observed from the end of August to the beginning of September, and H. japonica's peaks were observed at the beginning of June and mid-July. The number of C. kuwanae captured in the non-pesticide field was more than those in reduced pesticide and conventional control fields and the number of P. hareja captured in the reduced pesticide field was more than those in other fields.
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