Notes on the Occurrence of Pathogenic Races of <Emphasis Type="Italic">Xanthomonas oryzae </Emphasis>pv. <Emphasis Type="Italic">oryzae </Emphasis>Found in Hiroshima Prefecture in 1999

The pathogenic race of 59 cultures of Xanthomonas oryzae pv. oryzae, a pathogen of bacterial leaf blight of rice, isolated from six locations in the inland mountainous area of Hiroshima Prefecture in 1999, were determined by a set of traditional differentials. Four races—I, II, V and VII—were found across the area; however, we noticed the composition of the races as well as the dominant race in each location different. All races were avirulent on differential cultivar Te-tep. Races V and VII were new to Hiroshima. The rice cultivars infected with bacterial leaf blight in Hiroshima are thought to be grouped into the Kinmaze group, which does not have any resistance genes. Apparently, a variety of races occurred unexpectedly on the cultivars contrary to stabilizing selection theory. Received 25 February 2000/ Accepted in revised form 13 July 2000     

Production of triploid eastern little tuna,Euthynnus affinis (Cantor, 1849)

Herein, we developed a triploidization method using spawned eggs collected immediately after spawning of eastern little tuna (ELT), Euthynnus affinis. ELT broodstock induced the spawning by hormonal treatment in the tank, with the resulting spawned eggs being used for the triploidy induction. Under optimal conditions, the mean ± SEM triploidization and hatching rates were 97.2 ± 2.8% and 84.5 ± 10.3%, respectively. Although triploid ELT showed growth performance equivalent to that of diploids, the triploids died at a higher rate than the diploids during 2–4 weeks post‐hatching when triploids and diploids were reared in the same tank. Therefore, we propose that it would be necessary in a practical operation to use triploid‐only ELT seedlings to avoid selective cannibalism by the diploids. The ELT triploids exhibited an all‐female phenotype. Because previous studies have reported that female triploids show a greater probability of sterility than male triploids, this characteristic could be a major advantage. Since this triploidization method, using spawned eggs, can be performed without handling the broodstock, it is possible to avoid the physical damage caused by the process of artificial insemination, making it possible to repeatedly produce triploid populations without valuable broodstock loss. Thus, we have developed an efficient method to produce ELT triploids, although further study is essential to evaluate sterility of the triploid ELT.     

Effect of exudate released from seeds and seedling roots of common bean (Phaseolus vulgaris L.) on proliferation of Rhizobium sp. (Phaseolus)

Effects of seed and root exudates obtained from common bean on the proliferation of Rhizobium sp. (Phaseolus) were examined in a combination of three plant cultivars with three Rhizobium strains. In the first experiment, seed or root exudate was mixed with an Andosol soil extract, and bacterial proliferation in the mixture was traced. Seed exudate was prepared from hydroponic solution used in seed imbibition for 24 h, and a series of root exudates was prepared from a hydroponic solution collected every 24 h from the initiation of rooting up to 96 h after rooting. Regardless of the common bean cultivars and Rhizobium strains used, Rhizobium population markedly increased of the 24 h of culture in the mixture containing seed exudates, whereas a negligible increase was detected in the mixture with root exudates. The mixture containing root exudates collected within a period of 72–96 h after initial rooting (96–120 h after seed imbibition) exerted an inhibitory effect on Rhizobium proliferation. The seed exudates contained large amounts of sugars, amino acids, nitrogen, phosphorus, potassium, and magnesium compared to any root exudates. In the second experiment, Rhizobium was inoculated directly to common bean seeds sowed in a vermiculite bed which was sterilized and moistened with a plant nutrient solution. Compared with the control (without seed), a remarkable increase in the number of bacterial cells was observed in all the combinations of plant cultivars and Rhizobium strains 24 h after sowing. These results reveal that seed exudates of common bean have a substantial potential to promote Rhizobium proliferation, and that root exudates in a particular period of culture contain some inhibitory factors.     

Contribution of enhanced efflux to reduced susceptibility of Salmonella enterica serovar Choleraesuis to fluoroquinolone and other antimicrobials

We examined antimicrobial susceptibility and efflux systems in laboratory-derived mutants of Salmonella enterica serovar Choleraesuis selected by culture on fluoroquinolone-containing plates. The mutants exhibited decreased susceptibilities to quinolones and several other antimicrobials. Mutations in the gyrA gene were not always found in the mutants. Accumulation assays revealed that intracellular enrofloxacin concentrations were significantly lower in the mutants compared with parent isolates. Increased expression of acrB mRNA can explain the decreased susceptibilities to several antimicrobials but not in the case of carbonyl cyanide m-chlorophenylhydrazone (CCCP). Decreased susceptibility to CCCP may result from the increased expression of emrA mRNA. These results suggest that the enhancement of multiple efflux pumps is responsible for decreased susceptibilities to several antimicrobials in the laboratory-derived mutants.     

Growth of tiger puffer Takifugu rubripes in closed recirculating culture system

ABSTRACT:   Two feeding experiments were conducted to elucidate growth performance of tiger puffer in a 10 m³ water volume closed system. In experiment 1, 1000 fish of 3.5 g average body weight were fed tiger puffer commercial feed twice daily to apparent satiation, 6 days a week for 224 days. Sand-filtered sea water was used and no water was exchanged during the rearing period. Immediately after cutting of lower teeth at day 112, daily feed consumption decreased greatly and 60 fish died in few days. Feeding rates recovered and then decreased gradually as nitrate levels increased from 600–1048 mg N/L. Fish grew to 343 g with 91% survival rate and 87% feed efficiency. Rearing conditions of experiment 2 were similar to experiment 1, except that culture water was exchanged to maintain the nitrate level less than 600 mg N/L during the 224-day experiment. Mortality and reduction of feed consumption occurred immediately after teeth cutting as was observed in experiment 1. Significant reduction of feed intake was not found during other rearing periods. Fish of 3 g grew to 303 g with 91% survival rate and 72% feed efficiency.     

Effects of fish size and water temperature on the acute toxicity of boron to Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> and red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis>

ABSTRACT:     The acute toxicities of boron were examined for Japanese flounder Paralichthys olivaceus and red sea bream Pagrus major in terms of fish size and water temperature. Japanese flounder of 0.1–70.0 g and red sea bream of 0.6–20.3 g were exposed to different concentrations of boron for 96 h at 20°C under semi-static conditions. In both fish species, the median lethal concentration (LC₅₀) for 96 h of boron increased linearly with increasing fish size, ranging from 108 to 252 mg B/L for the flounder, and from 97 to 172 mg B/L for the sea bream. The effect of water temperature on acute toxicity was examined for Japanese flounder of 0.6 and 1.5 g at 10, 15, 20 and 25°C, and for red sea bream of 0.6 and 2.4 g at 12, 15, 20 and 25°C. The toxicity of boron for the flounder increased linearly with increasing water temperature. The 96 h LC₅₀ values ranged from 299 to 108 mg B/L for the 0.6 g flounder and from 350 to 113 mg B/L for the 1.5 g flounder. A similar trend was shown for the 2.4 g red sea bream; however, the relationship for the 0.6 g red sea bream was not significant.     

Isoxaben analogs inhibit chitin synthesis in the cultured integument of the rice stem borer Chilo suppressalis

Benzoylphenylureas (BPUs) were discovered as novel type insecticides about a half century ago; many analogs have been launched as insecticides and acaricides. BPUs are known to inhibit chitin synthesis in insects and other arthropods, but they have no effect against microorganisms such as fungi. We designed new chitin synthesis inhibitors based on the hypothesis that biomolecules that play important roles in cellulose and chitin biosynthesis are similar. In the full automatic modeling system (FAMS), the cellulose synthase was selected as a template three-dimensional structure. Thus, we focused on the structure of cellulose synthase inhibitor, isoxaben, to develop new chemistry. The 1,1-diethylethyl [-C(CH₃)(CH₂CH₃)₂] group of isoxaben was changed to a 4-substituted phenyl group bearing Cl, Et, or Ph. These compounds significantly inhibited chitin synthesis in the cultured integument of the rice stem borer Chilo suppressalis. The activity of the 4-ethylphenyl analog was enhanced 30-fold by adding piperonyl butoxide to the culture medium.     

Nonsteroidal ecdysone receptor agonists use a water channel for binding to the ecdysone receptor complex EcR/USP

The ecdysone receptor (EcR) possesses the remarkable capacity to adapt structurally to different types of ligands. EcR binds ecdysteroids, including 20-hydroxyecdysone (20E), as well as nonsteroidal synthetic agonists such as insecticidal dibenzoylhydrazines (DBHs). Here, we report the crystal structures of the ligand-binding domains of Heliothis virescens EcR/USP bound to the DBH agonist BYI09181 and to the imidazole-type compound BYI08346. The region delineated by helices H7 and H10 opens up to tightly fit a phenyl ring of the ligands to an extent that depends on the bulkiness of ring substituent. In the structure of 20E-bound EcR, this part of the ligand-binding pocket (LBP) contains a channel filled by water molecules that form an intricate hydrogen bond network between 20E and LBP. The water channel present in the nuclear receptor bound to its natural hormone acts as a critical molecular adaptation spring used to accommodate synthetic agonists inside its binding cavity.     

Early growth of hinoki (<Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>) trees under different topography and edge aspects at a strip-clearcut site in Kyushu,Southern Japan

The positive and negative effects of the residual stand edge at a strip-clearcut site were examined on the initial growth of hinoki (Chamaecyparis obtusa) planted in areas with diverse topography. On the south edge, the gap light index was lower than on the north edge and strip center; however, the vapor pressure deficit was also lower than on the north edge and strip center, which resulted in lower physiological stress of hinoki on the south edge. Tree size on the south edge did not exceed that on the north edge and strip center. These results indicated that low light conditions due to residual trees negatively affected growth on the south edge even under the positive effect of microclimate alleviation. In valley, tree size in the second year after planting was smaller than on ridge and slope; however, tree growth during the following 2 years was higher in valley. Surface soil in valley was thinner with rockier substrates than on ridge and slope; that is, soil sedimentation type and substrates influenced the initial growth of hinoki with undeveloped roots, and after that, topography started to influence growth, probably because hinoki roots penetrated into deeper soil, which is influenced by the water gathering capacity of the valley. The initial growth of hinoki at the strip-clearcut site was predominantly affected by light rather than microclimate alleviation. This alleviation is expected to disappear when hinoki trees planted in the strip center grow enough to give additional shade to slow-growing edge hinoki.