Contamination of internationally traded wheat by herbicide‐resistant Lolium rigidum

As herbicide‐resistant weeds have spread in the agricultural fields of grain‐exporting countries, their seeds could be introduced into other countries as contaminants in imported grain. The spread of resistance genes through seed and pollen can cause significant economic loss. In order to assess the extent of the problem, we investigated the contamination by herbicide‐resistant annual ryegrass (Lolium rigidum) of wheat imported from Western Australia into Japan. Annual ryegrass seeds were recovered from wheat shipments and seed bioassays were conducted to identify resistance to the herbicides that are commonly used in Australia: diclofop‐methyl, sethoxydim, chlorsulfuron, and glyphosate. Nearly 4500 ryegrass seeds were detected in 20 kg of wheat that was imported in both 2006 and 2007. About 35% and 15% of the seeds were resistant to diclofop‐methyl, 5% and 6% were resistant to sethoxydim, and 56% and 60% were resistant to chlorsulfuron in 2006 and 2007, respectively. None was resistant to glyphosate in either year. As the contamination of crops by herbicide‐resistant weeds is probably a common phenomenon, the monitoring of incoming grain shipments is necessary to stem the further spread of herbicide‐resistant weeds into importing countries.     

Histological observations of seasonal reproductive and lunar-related spawning cycles in the female honeycomb grouper Epinephelus merra in Okinawan waters

Seasonal reproductive and lunar-related spawning cycles of the female honeycomb grouper Epinephelus merra inhabiting Okinawan waters were examined by histological observation of ovaries. Gonadosomatic index (GSI) increased beginning in May and peaked in June. Histological observations revealed that many oocytes laden with yolk were present in the ovaries from May to August. From September to October, ovaries were occupied by immature oocytes. These results suggest that the reproductive season of E.   merra lasts for 4 months from May through August in Okinawan waters. When the fish were collected according to the lunar cycle, GSI increased with the approach of the full moon. Oocytes at various development stages were observed from the first quarter to the full moon. Fresh ovulatory follicles were present in the ovaries around the last quarter moon. These results suggest that E.   merra has a lunar spawning cycle and spawns between the full moon and the last quarter moon. Ovarian features of the fish collected around the last quarter moon were different among individuals; some fish had many oocytes at the tertiary yolk stage in the ovaries, while the ovaries of the others were occupied by the oocytes at the peri-nucleolus and the oil droplet stages. This observation suggests that a minor release of eggs occurs in this species before or after a major spawning lunar day. Oocytes at the migratory nucleus and the maturation stages were not observed in any ovarian samples. This may mean that maturation of oocytes is related to the spawning behavior of this species and makes rapid progress in the process of aggregation at the spawning sites.     

Comparison of in vitro vitellogenin synthesis among different nonylphenol products using primary cultures of tilapia hepatocytes

Effect of nonylphenol (NP) products from different companies on in vitro vitellogenin (VTG) synthesis was compared using tilapia ( Oreochromis mossambicus ) hepatocytes cultures. Addition of NP at a concentration of 10⁻³ M to the medium caused death of hepatocytes (NP-A and NP-B) and delay of monolayer formation (NP-C). No cell death was observed at a concentration of 10⁻⁴ M (NP-A, -B and -C) but cell adhesion was slower than control. These results suggest that high concentration of NP is toxic against tilapia hepatocytes. When effects of estradiol-17β (E₂, 10⁻⁷ M) and NP (10⁻⁴ M) on in vitro VTG synthesis were examined, addition of E₂ and NP-A and NP-B to the media resulted in elevation of VTG. NP-C did not induce VTG in the medium. Co-treatment of NP-B and tamoxifen, a non-steroidal anti-estrogen, reduced VTG synthesis. These results suggest that NP has estrogenic potential in primary cultures of tilapia hepatocytes and acts through binding to the estrogen receptor, and that there is a difference in the induction level of VTG among different NP products.     

Oogenesis in the common Japanese conger Conger myriaster

ABSTRACT:    We investigated the process and characteristics of oogenesis in the common Japanese conger Conger myriaster . Young fish caught in November 1996 were reared for use in this experiment. Fish were sampled monthly from December 1997 to August 1998. Some were injected with human chorionic gonadotropin to stimulate ovarian maturation from May to August 1998. Oocytes from the chromatin nucleolus stage to the secondary yolk globule stage were obtained from non-hormone-treated fish; those of more advanced stages were obtained from hormone-treated ones. We divided oocyte development into eight stages from the chromatin nucleolus stage to the maturation stage. The yolk vesicle stage was not separated because yolk vesicles began to appear just after appearance of yolk globules. Oocyte, oil droplet, yolk globule and nucleus diameters all increased concomitant with oocyte development. Oil droplet and yolk globule diameters increased remarkably at the maturation stage. However, zona radiata thickness peaked at the secondary yolk globule stage, decreasing gradually thereafter. Increased gonadosomatic index was related to oocyte development as found in European and Japanese eels receiving hormone treatment to mature. The present study is the first report describing oogenesis characteristics in congrid eels. It indicates that oogenesis is almost identical to that of other anguillid eels.     

Development of embryos and larvae in the common Japanese conger Conger myriaster

Development of embryos and larvae in the common Japanese conger Conger myriaster was observed after artificial fertilization. Eggs were obtained from females matured artificially by hormone injections and milt was obtained from males matured naturally. Fertilized eggs were kept in seawater at 12–14°C. The first cleavage occurred at 4 h, epiboly began at 24 h, the embryonic body was formed at 38 h and hatching occurred at 84 h after insemination. Newly hatched larvae were approximately 2.5 mm (total length) and similar to those of Anguilla japonica in terms of external features. The mouth and anus opened on the 7th day after hatching. Pigments began to appear at the tip of the tail on the 10th day. The total length of the larvae reached approximately 8 mm on the 11th day. Eye pigmentation began on the 14th day. One larva lived for 19 days without food.     

Allelopathic effect of leaf debris, leaf aqueous extract and rhizosphere soil of Ophiopogon japonicus Ker-Gawler on the growth of plants

Laboratory and greenhouse experiments were conducted to evaluate the allelopathic potential of dwarf lily turf ( Ophiopogon japonicus Ker-Gawler) on lettuce, alfalfa, timothy and mustard plant growth. Dry leaf debris, aqueous extract of fresh leaves and O. japonicus grown soil were investigated. Emergence, dry weight, and root and shoot length of all bioassay species were inhibited when grown in soil incorporated with oven-dried leaves of O. japonicus. The inhibitory effects were often dependent on the concentration. However, the degree of inhibition varied among the test plant species. The aqueous leaf extract was highly phytotoxic and it significantly reduced germination, seedling growth, and the fresh weight of all the test species at all rates. The emergence and growth of all four tested plants were severely inhibited when planted in O. japonicus contaminated soil. These results indicate that O. japonicus incorporated leaf debris, leaf aqueous extract and its rhizosphere soil suppress seed germination, radicle growth, seedling emergence and seeding growth of certain weeds and suggest that these responses were attributed to an allelopathic effect.     

Physiochemical factors affecting the salt tolerance of Echinochloa crus-galli Beauv. var. formosensis Ohwi

The effects of NaCl-induced stress on physiochemical factors such as inorganic cations, proline, malondialdehyde (MDA) and polyamines were investigated in the gramineous weed, Echinochloa crus-galli Beauv. var. formosensis Ohwi ( E. crus-galli ) and rice ( Oryza sativa L. cv. Nipponbare). Growth inhibition at the 2nd leaf stage under salt stress was more severe in rice than in E. crus-galli . Water content in the 2nd leaves was also more severely decreased in rice, indicating that E. crus-galli was more salt-tolerant. After NaCl treatment, Na⁺ accumulated in the 2nd leaves of both plant species but not in their roots. Proline accumulation in the 2nd leaves was significantly higher in salt stressed E. crus-galli than in rice, suggesting the significance of proline production in the salt tolerance of this weed. Content of MDA of the rice increased more greatly with NaCl treatment than that in E. crus-galli . NaCl treatment affected polyamine metabolism of both plant species, but the response of each plant to salt stress was somewhat different, especially in the leaves. Leaf putrescine and spermidine contents were high in non-stressed plants in salt-sensitive rice, although rather lower in E. crus-galli in response to NaCl concentrations. These results indicate that an increase in proline and changes in polyamines relates to the salt tolerance of E. crus-galli .