More effective seed disinfection methods to control rice blast are needed due to the occurrence of MBI-D resistant strains of Pyricularia grisea in Kyusyu district. Seed disinfection with a tank mixture of DMI (a combination of ipconazole and copper hydroxide) and benomyl was found to be highly effective against seedling rice blast from infected seed. More importantly, in the paddy field where these seedlings were transplanted, the leaf blast was also effectively controlled. The rep-PCR fingerprint analyses showed that most of the isolates obtained from the leaf blast in the paddy field had the same haplotypes as that obtained from the remaining seedlings. These results suggested that leaf blast in the paddy field was effectively prevented by intercepting the import of infected seedlings with transplantation.
To investigate the genetic diversity of Kyuri green mottle mosaic virus (KGMMV) in Kyushu, Japan, nine isolates collected from greenhouse-cultivated cucumbers from 2005 to 2009 were examined. All isolates showed mosaic and growth inhibition on cucumber plants after mechanical inoculation. Phylogenetic analyses of the nucleotide sequences of the coat protein (CP) and movement protein (MP) genes clustered the nine isolates into four groups. For the CP gene, one cluster consisted of two isolates and the other three clusters were closely related to the Yodo and Cucumber strains. This was not the case for the MP gene. Recombination analysis of the genomic region encoding MP and CP suggested that recombination events had occurred among isolates within the same cluster. These data indicate that there is a high genetic diversity among KGMMV populations in Kyushu and some isolates have been generated by recombination.
Fruit rot in loquat (Eriobotrya japonica) was suppressed effectively by covering the roof of the plastic greenhouse with polyethylene film early in the season. Early roof covering intercepted rain during the flowering stage of loquat. The fungi that caused fruit rot were primarily Pestalotiopsis sp. and Colletotrichum sp., although other fungi were also observed on some rotten fruits. This control practice was statistically estimated to reduce the risk of fruit rot to as low as 20% of that using conventional practices.
Polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP), and quantitative PCR (qPCR) were used to detect low-level Candidatus Liberibacter asiaticus infection in citrus trees, and their results were compared. Sample DNA was prepared from the developing shoots of Citrus depressa and Citrus tankan that were spontaneously infected with Ca. L. asiaticus. The concentrations of the homologous region of the tufB gene of Ca. L. asiaticus were estimated by qPCR analysis using serially diluted plasmid DNA containing the tufB gene region as a calibration standard. All DNA samples from which the specific amplification product was detected by PCR also gave positive results in the LAMP analysis, and qPCR gave positive results for all samples that were positive in the LAMP analysis. Therefore, we concluded that qPCR is the most sensitive method for detecting low-level Ca. L. asiaticus infection.
In Japan, citrus greening is routinely diagnosed using PCR amplification of DNA fragments of the pathogenic bacterium ‘Candidatus Liberibacter asiaticus’ (Ca. Las). The temporal change in the distribution of PCR-positive tissue within a canopy of Citrus depressa was examined in five trees in Okinawa for 1 year, using the MHO 353/354 primer set. During spring and summer, Ca. Las was detected most frequently from samples collected in May by PCR. There was little difference in the frequency of detection of Ca. Las among petals, peduncles, the bark of twigs, and the midribs of leaves. The frequency of detection varied from one sub-main branch to another. Sub-main branches that showed a high frequency of detection maintained the trend throughout the year. The frequency of detection remained unchanged at low levels in some sub - main branches, whereas it increased later in other sub-main branches. There was little association between the frequency of detection within a sub-main branch and the degree of foliar symptoms on the branch. Based on these observations, the optimum sampling methods for detecting Ca. Las from a suspected tree by PCR, which includes pooling of several leaf samples for a single DNA extraction, is discussed.
New blight-like symptoms in the native moss Bryum argenteum were first found on plants growing in a gutter in Omura, Nagasaki, Japan on June 24,2008. White mycelia and rapeseedsized, brown, spherical sclerotia were observed on the diseased plants. A fungus similar to Sclerotium rolfsii was isolated from the infected parts. The mean optimum temperature for mycelia growth of the isolates on potato sucrose agar medium was 25°C and that for sclerotium formation was 30°C; the mycelial tufts were white to grayish brown, with the main hyphal width ranging from 4.3 - 7.9 μm ; clamp connections were observed. These mycological characters were identical to those of S. rolfsii reported in other plants. The isolates were found to be pathogenic to B. argenteum in an artificial inoculation test, and could be re-isolated. Therefore, Koch' s postulates were satisfied. We proposed that this disease be called southern blight of B. argenteum caused by S. rolfsii.
As a part of our investigation to elucidate the population biology of the apple snail Pomacea canaliculata inhabiting irrigation canals, we monitored the number of snails escaping from a paddy field into an irrigation canal in Kamimine Saga, South Japan. We installed a net trap on one of the two drainage pipes in a paddy field(60 a). The number of snails trapped in the net was counted twice or three times a month during crop season (from late June to early October, 2008). Totally, 265 overwintered snails that had hatched in the previous season were trapped in the whole season. Snails of the new generation were trapped from August onwards and a total of 470 young juveniles with shell height more than 8 mm escaped from the paddy field until the end of the crop season. According to the size specific densities of snails in the paddy field, we estimated that more than several thousand snails with shell height smaller than 8 mm likely escaped through the wide mesh of the net trap and into the canal. The number of snails caught in the net had a significant correlation with the precipitation. The snails were considered to have escaped from the paddy field when paddy water overflowed into the canal. Many similar paddy fields were connected to the canal, and we therefore suspect that huge numbers of snails entered the canal from the fields. It raises a question how the escape of apple snails from paddy fields influences their population in the canals.
Maize wallaby ear symptom (MWES) is caused by the maize orange leafhopper Cicadulina bipunctata, which feeds on various Poaceae plants. We examined the effects of C. bipunctata infestation on 6 summer-seeding forage crops. Swelling of leaf veins, which is the characteristic symptom of MWES, was not observed in infested plants of the orchard grass Dactylis glomerata, sorghum Sorghum bicolor, Rhodes grass Chloris gayana, Sudan grass Sorghum sudanense, and guinea grass Panicum maximum, although significant growth suppression occurred in the orchard grass and Rhodes grass. However, strong growth suppression and severe swelling of leaf veins was observed in all varieties of the oats Avena sativa and A. strigosa that were infested by C. bipunctata, indicating that MWES could occur in oats as well as in the maize Zea mays. Both adult and nymph C. bipunctata individuals could feed on orchard grass, sorghum, Sudan grass, and oats, indicating that these 4 crops could be the host plants of C. bipunctata. Because MWES clearly affected oats but not the other 3 crops, it seems that development of MWES on feeding plants is not indispensable for the survival of C. bipunctata.
Variation in the egg mass size of Hypera postica was examined in relation to the stem diameter of Astragalus sinicus collected at Hioki, Kagoshima Prefecture, in 1993. The number of eggs per egg mass varied from 1 to 48 (mean=11.7) ; the number of egg masses containing 4-6 eggs accounted for 23% of the total egg mass number. The frequency distribution of egg mass sizes was similar to a lognormal distribution, and a clear relationship between the stem diameter of A. sinicus and egg mass size was not detected.
We measured the egg period of Euscepes postfasciatus at two incubation temperatures, 25°C and 20°C, and under several schedules that differed from each other with regard to the durations of the two temperatures. The peak egg hatch at 25°C was observed at 8 d after oviposition, and that at 20°C at 15 d after oviposition. As the duration of incubation at 25°C was decreased from 6 d to 1 d, the peak hatch delay extended from 9 d to 14 d after oviposition, indicating that the egg period of the species can be controlled from 8 d to 15 d. The hatchability did not vary significantly among the different incubation schedules; thus, this method for controlling the egg period of E. postfasciatus can be used for artificial rearing of the species without adverse effects on insect survival.
To improve the artificial rearing technique for Euscepes postfasciatus, we investigated the effects of surface processing of artificial diets before egg seeding and the type of absorbent paper placed on the diet after egg seeding on survival and development of the species. Two surface-processing methods (grooving in a cross-hatched pattern and punching many holes) and two types of absorbent paper (Kimwipes® and filter paper) were tested. Compared to the diet that was not surface processed, neither grooving nor punching significantly affected the survival rate when Kimwipes was used. When the diet surface was grooved, the survival rate with the use of filter paper was comparable to that with the use of Kimwipes; when the filter paper was used with non-processed or punched diet, the survival rate drastically decreased. A combination of non-processed diet and Kimwipes was considered to be the best for mass rearing of E. postfasciatus in terms of ensuring a higher survival rate of insects and reducing labor cost.
The effects of irradiation on copulatory and oviposition behavior in the sweetpotato weevil , Cylas formicarius (Fabricius) were evaluated using females irradiated with 50 Gy gamma rays during the pupal stage, females irradiated at 200 Gy during the adult stage, and non-irradiated normal females. All types of females copulated with males irradiated during the adult stage or normal males. The females irradiated during the pupal stage did not complete oviposition or produce offspring after copulation when paired with irradiated or normal males, similar to females that did not copulate. The females irradiated during the adult stage exhibited oviposition behavior during a short period just after copulation but gradually stopped , and none produced offspring. Normal females that copulated with males irradiated during the adult stage laid eggs but produced no offspring, whereas they produced offspring when mated with normal males. These results can be used to estimate the competitive ability of released males irradiated during the adult stages against wild males. Using a normal virgin female trap in the field, her copulatory experience and partner can be detected; i.e. , if the female lays eggs, then this indicates she has copulated, and if she fails to produce offspring, this indicates that she has copulated with a released male irradiated as an a adult.
The spider mite, Tetranychus takafujii Ehara & Ohashi, was found in Tokyo, Osaka, Kyoto and Hyogo in Honshu in 2002, and in Kagoshima, Kyushu in 2007. PCR-RFLP analysis of the rDNA ITS 2 gene used to discriminate T. evansi from T. urticae identified T. takafujii from among 11 congeneric Japanese mite species. Our field surveys revealed that T. takafujii was distributed in Fukuoka of Fukuoka Prefecture, many areas of Kagoshima Prefecture, and on Irabujima Island, Okinawa Prefecture. In these areas, T. takafujii occurred on Solunum nigrum, S. carolinense, S. melongena, S. americanum, S. lycopersicum, S. lycopersicum var. cerasiforme, S. tuberosum and Physalis alkekengi var. franchetii.
The spider mite, Tetranychus takafujii Ehara and Ohashi,2002, is known to occur mainly on weeds and black nightshade in Tokyo, Osaka, Kyoto and Hyogo prefectures on Honshu island. In 2007, T. takafujii was found to cause heavy damage to cherry tomatoes in Kagoshima on Kyushu island. To test the possibility of chemically controling this spider mite, we tested its susceptibility to 18 acaricides/pesticides available for tomato and other vegetables in the Solanaceae using a leaf dip method. Spider mite females were highly susceptible to most acaricides/pesticides, except Etoxazole SC and Spirodiclofen SC which are categorized as slow-acting. Spider mite eggs were also highly susceptible to many of treatments, except Malathion EC, Bifentrin 2.0% WP, Emamectin benzoate EC, Chlorfenapyr SC and Bifenazate SC. Egg hatchability at day 4 were ranged from 24.7% to 89.4% among the treatments, and most neonate larvae died after 1 day of Emamectin benzoate EC, Chlorfenapyr SC and Bifenazate SC treatments. Results suggest that many of the treatments tested will be effective in controlling of T. takafujii either at the egg, larval or adult stage.
In southwestern Japan, the Japanese mealybug Planococcus kraunhiae (Kuwana) (Hemiptera: Pseudococcidae) is one of the most serious pests that attack the Japanese persimmon Diospyros kaki Thunb. (Ebenaceae). Diadiplosis hirticornis (Felt) (Diptera: Cecidomiidae) is thought to be an important natural enemy of P. kraunhiae. In order to establish control measures that use D. hirticornis to control the population of the mealybug, we need fundamental information on the ecological and behavioral characteristics of D. hirticornis. As the first step, we investigated its developmental velocity at 17.5, 20, 22.5, 25, 27.5, 30, and 32.5°C and its hourly adult emergence pattern. The lower developmental threshold was found to be 11.1°C for both male and female individuals. For the whole stages from egg to adult, the day-degrees above the developmental threshold was 232.6 for male and 238.1 for female individuals. D. hirticornis was confirmed to be diurnal. A majority of the males emerged between 6 : 00 and 12 : 00, while most females emerged between 8 : 00 and 18 : 00.