An inoculation method for confirming the pathogenicity of Pseudomonas syringae pv. japonica (synonym pv. syringae), causal agent of bacterial black node of barley and wheat was developed. The plants at flag leaf stage were each placed at 20-25 ℃ for about five hours in a dark container, then 10 µl bacterial suspension was dropped on the auricle at several points in time around the stage. The inoculated plants were placed at 20-25 ℃ for three days in a dark container and then placed for one week with appropriate light and humidity. The infection frequency by this inoculation method was the highest on the plants inoculated during flag leaf expansion stage, while it decreased when the plants were inoculated at the beginning of heading stage. When plants of 14 cultivars of wheat and 11 cultivars of barley were each inoculated with the pathogen during flag leaf expansion stage, disease symptoms were formed on all the cultivars. These results suggested that wheat and barley were more susceptible to bacterial black node pathogen during flag leaf expansion stage irrespective of cultivar type. The disease mainly occurred on the leaf sheath as withering with black lesions forming under the inoculated point, but several plants also showed black lesions on the stem, followed by stem breaking, as well as ear burn. These symptoms are identical with those found in the field, indicating that bacterial black node disease can be reproduced by the inoculation method.
Broccoli plug seedlings in Kagawa Prefecture, Japan, in 2014 and 2015, wilted and damped-off. A microorganism was isolated from stems of the diseased plants and identified as Pythium megalacanthum by morphological and molecular phylogenetic analysis. When the microorganism was inoculated onto broccoli plug seedlings, it produced identical symptoms to the original infection and the microorganism inoculated was re-isolated from the diseased plants. Thus, the causative pathogen was identified as P. megalacanthum. This is the first report of broccoli disease caused by this microorganism in Japan.
Spinach cultivars reaction to Peronospora farinosa f. sp. spinaciae isolate SAI-2, suspended race numbering, obtained from Saitama Prefecture, Japan in 2010 were studied. It was suggested that commercial cultivars resistant to race 8 had also potential for resistance against the pathogenic strain involving isolate SAI-2.
In April 2015, irregularly and yellowing lesions on the leaves of shepherd’s purse (Capsella bursa-pastoris) were found in an outdoor field in the south area of Ibaraki Prefecture. White and powdery stigmata of this pathogen were observed on the lesions. The pathogen of this disease was identified as Hyaloperonospora parasitica based on the morphological features of conidia and conidiophores, host range and the sequence of ribosomal DNA internal transcribed spacer (rDNA-ITS) region.
To develop an assay using reverse transcription polymerase chain reaction (RT-PCR) to detect multiple species of viruses in the Tospovirus genus, six primer pairs were chosen from those previously reported and tested to determine if RT-PCR with these primers could detect 8 species occurring in Japan. Consequently, two primer sets, gL2740/gL3920 or t2740/t3920c could detect all species occurring in Japan. The nucleotide residues of t2740 and t3920c were modified to correspond with each of the target sequences of 19 species reported outside Japan, except Groundnut chlorotic fan-spot virus. RT-PCR with the modified primer pair resulted in detecting the 8 species occurring in Japan, and was expected to be available for multiple species in the Tospovirus genus.
Abstract We investigated the effectiveness of augmentation of the mirid bug Nesidiocoris tenuis (Reuter) against the greenhouse whitefly Trialeurodes vaporariorum (Westwood) on tomatoes in greenhouses by pre-plant or post plant releases. In trial 1, the tomatoes were transplanted in May 2014, and the bugs were released three times after transplanting at weekly intervals with a density of 0.5 bugs per plant. In trials 2 and 3, the bugs were released two times before transplanting at weekly intervals with a density of 0.5 bugs per plant in August 2014 or in May 2015. In each trial, N. tenuis colonized the tomato plants. The density of whitefly on tomatoes was significantly lower in the bug-released greenhouse (Repeated measures of ANOVA, p < 0.0001) than in the non-released greenhouse. Nesidiocoris tenuis did not cause economic damage to tomato. These results indicate that pre-plant or post-plant releases of N. tenuis are effective for controlling T. vaporariorum on tomatoes in greenhouses.
Abstract We investigated the population dynamics of Nesidiocoris tenuis (Reuter) and recorded species of other insects observed on sesame in 2014 and 2015 in Chiba Prefecture, Japan. Nesidiocoris tenuis adults and nymphs occurred during or after the second half of August until the end of October or plant death. We observed one lepidopteran pest and four hemipteran species (except N. tenuis) including three pest species of some crops. These results indicated that sesame plants are potentially useful for collecting N. tenuis in a field in Chiba Prefecture. However, we should pay attention to occurrence of insect pests.
Abstract A new pest, Welsh onion root darkwinged fungus gnat (tentative name) (Bradysia sp.) injurious to Welsh onion in fall and winter, and carrot in spring in the northern part of Saitama Prefecture, its distribution on parasitized Welsh onion plants and susceptibility to insecticides were investigated. Welsh onion was primarily parasitized by larvae at the stem plate, but the number of larvae increased at the leaf sheath covered with soil increased by soil covering work. As a result of examining the susceptibility of the larvae to insecticides registered on Welsh onion in laboratory conditions, 8 insecticides had a corrected mortality rate of 70% or more out of 30 insecticides; Thiodicarb WP, Clothianidin WS, Cypermethrin E, Dinotefuran WS, Fulfenokthlon E, Lufenuron E. Methomyl WP, and Tephrtorin G.
We investigated the density fluctuation of Thrips tabaci Lindeman and Gynaeseius liturivorus (Ehara) on Welsh onion and Anaphothrips obscurus (Müller) and G. liturivorus on intercropping barley‘Hyakumangoku’ in 2013 and 2014 in Chiba Prefecture, Japan. Gynaeseius liturivorus densities on barley increased in late July after peak abundance of A. obscurus. Densities of G. liturivorus and T. tabaci on Welsh onion intercropping with barley in late July was significantly higher and lower than on Welsh onion without barley (=control), respectively. Barley plants sowed in late May or early June in this experiment withered in late August. Gynaeseius liturivorus densities on Welsh onion intercropping with barley rapidly decreased after barley plants withered, and it shifted similarly or lower than on control Welsh onion in October to November. Thrips tabaci densities on Welsh onion intercropping with barley shifted equally on control Welsh onion after October. These results indicated that intercropping barley increases G. liturivorus density and decreases T. tabaci density on Welsh onion in late July. However, we need techniques to maintain high G. liturivorus density to control and lower T.tabaci density after intercropping barley plants withered.
We investigated the life history and the natural enemies of the coconut scale, Aspidiotus destructor Signoret (Hemiptera: Diaspididae), in some commercial tea fields from 2015 to 2017 in Shizuoka Prefecture, Japan. The periods of egg deposition and their hatching were observed three times a year: from late April to late May, one month in July, and from late August to late September, and most of overwintering stages were female adults. This result suggested that A. destructor occurs with three generations a year in tea fields. Total number of eggs per female of the overwintering generation was 58.7±2.8 (n=25). Four species of parasitoids emerged from the scale females collected in tea fields. The dominant species were two species, Encarsia citrine (Craw) and Aphytis diaspidis (Howard). It was observed that percentage parasitism by the dominant two species was sometimes over 90%, although it changed according to the season. We also found a kind of ladybird: Pseudoscymnus hareja (Weise) andpredaceous gall midge (this species may be Dentifibula viburni (Felt) as predatory insects against the scale.
Damage caused by western flower thrips Frankliniella occidentalis occurred on young fruits of kumquat Fortunella crassifolia in a greenhouse. Many white points observed on the fruits seemed to be caused by oviposition. By releasing the adults to young fruits, we demonstrated that the damage was caused by females infesting from 1 – 3 weeks after blooming.
Abstract The population density of yellow tea thrips Scirtothrips dorsalis is influenced by the quantity of young shoots for feeding and oviposition. In this study, the effect of trimming windbreaks of bigleaf podocarp trees on the occurrence of the thrips was investigated in citrus orchards. Trimming in mid-June resulted in an increase of the thrips adults and larvae on the windbreaks from mid-July to early August caused by the continuous growth of young shoots.