Identification and use of a wild plant with antimicrobial activity against Ralstonia solanacearum, the cause of bacterial wilt of potato

Fresh aerial tissue and roots of 14 wild plants in Okinawa prefecture were investigated for their antimicrobial activity against Ralstonia solanacearum , which causes bacterial wilt of potato. A 70% aqueous ethanol extract of fresh aerial tissue of Geranium carolinianum L. showed strong antimicrobial activity against R. solanacearum . This extract also showed antimicrobial activity against the pathogens causing common scab of potato and soil rot of sweet potato. The antimicrobial substance could be extracted with hot water, and was effective against R. solanacearum in soil. In the field test, a treatment combining incorporation of dried aerial tissue into the soil and solarization was highly effective for control of bacterial wilt of potato. These findings suggest that G. carolinianum L. could be used as a biological agent for the control of bacterial wilt of potato.     

Control of soil rot of sweet potato by the incorporation of the fresh aerial tissue of Geranium carolinianum L. into the soil

In a previous study, we found that a 70% aqueous ethanol extract of the fresh aerial tissue of Geranium carolinianum L. showed antimicrobial activity against the pathogen causing soil rot of sweet potato. As the appropriate time for cultivation of sweet potato and the growing period of G. carolinianum do not overlap in Okinawa Prefecture, Japan, the fresh aerial tissue is available in order to control soil rot of sweet potato. Thus, we examined the control effect of fresh aerial tissue against soil rot of sweet potato. The various trials (a single repetition of 20 m²) were performed in fields that had undergone 8 years of continuous cropping of sweet potato at Okinawa Prefectural Agricultural Experiment Station, Horticultural branch. After harvest, when the disease severity was evaluated by determining the necrotic area of the storage root, the incorporation of fresh aerial tissue (5000 kg 1000 m^-2) into the soil was considered to be highly effective, with a protective value of 75.4. This result shows that G. carolinianum could be used as a biological agent for the control of soil rot of sweet potato.     

Lipid composition and deposition of cultured yellowtail Seriola quinqueradiata muscle at different anatomical locations in relation to meat texture

ABSTRACT:   The present study was undertaken to assess the lipid composition and deposition in muscle at three anatomical locations in cultured yellowtail and to investigate the effect of lipid composition and deposition on meat texture. Lipid deposition in muscle was studied by histochemical staining of lipid with Sudan dye. Lipid class composition analysis showed that neutral lipids were the main constituents of lipid in cultured yellowtail and accounted primarily for the variation in muscle lipid content with the anatomical location of meat, as well as with season, whereas the polar lipid content remained almost constant. Furthermore, muscle neutral lipid content was correlated negatively with meat breaking strength; however, no correlation was observed between muscle polar lipid content and meat breaking strength. The histochemical study revealed that, in yellowtail muscle, lipid is preferentially deposited in the myosepta and, with increases in muscle lipid content, additional fat is deposited along sparsely distributed thin connective tissue. It was also observed that the greater the lipid deposition in collageneous connective tissue, the lower the meat breaking strength; presumably, higher lipid deposition in the connective tissue resulted in weakening of the muscle structure.     

Identification and activity of ethyl gallate as an antimicrobial compound produced by Geranium carolinianum

We isolated an antimicrobial compound from the aerial tissue of Geranium carolinianum and identified it as ethyl 3, 4, 5-trihydroxy benzoate (ethyl gallate) by ¹H-NMR and ¹³C-NMR and gas chromatography–mass spectrometry. The antimicrobial activity of ethyl gallate against three potato pathogens was assayed by the paper disk method. The activity against Ralstonia solanacerum , Streptomyces scabies , and Streptomyces acidiscabies was observed at concentrations >200, >300, and >300 µg disk⁻¹, respectively. These results suggest that the antimicrobial activity of Geranium carolinianum against soil-borne plant disease pathogens is partly related to ethyl gallate.     

Environmental variability and growth histories of larval Japanese sardine (Sardinops melanostictus) and Japanese anchovy (Engraulis japonicus) near the frontal area of the Kuroshio

Environmental variability and growth‐rate histories from hatching to capture were investigated for larval Japanese sardine (Sardinops melanostictus) and Japanese anchovy (Engraulis japonicus). Larvae collected around the front of the Kuroshio Current were examined using otolith microstructure analysis, and their movement was estimated from numerical particle‐tracking experiments. Sardine larvae collected inshore of the Kuroshio front originated from a coastal area near the sampling site, while those collected in the offshore area originated from an area 500–800 km west‐southwest of the sampling site. Anchovy larvae collected both inshore and offshore had been transported from widely distributed spawning areas located west of the sampling area. At the age of 13–14 days for sardine and 19–20 days for anchovy, the offshore group exhibited significantly higher mean growth rates than did the inshore group. Although the offshore area was generally warmer than the inshore area, temporal variations in growth rate are not attributable solely to fluctuations in environmental temperature. While previous studies have examined the relationship between larval growth rates and environment based solely on data at capture, the methods used in the present study, combining otolith analysis and numerical particle‐tracking experiments, utilize data up until hatching. Although the relationship between growth rate and environment was not fully confirmed, this approach will greatly advance our understanding of fish population dynamics.     

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.     

Spatial distribution of the Japanese common squid, Todarodes pacificus, during its northward migration in the western North Pacific Ocean

The spatial distribution of Todarodes pacificus in and near the Kuroshio/Oyashio Transition Zone during its northward migration was examined by comparative surveys using two types of mid‐water trawl net and supplementary squid jigging from June to July 2000. The vertical and horizontal distribution patterns varied for different body sizes in relation to the oceanographic structure. Todarodes pacificus of 1–20 cm dorsal mantle length (ML) were widely distributed from the coastal waters of Japan to near 162°E longitude, probably due to transport by the Kuroshio Extension (KE). Todarodes pacificus smaller than 10 cm ML were mainly distributed in temperate surface layers at sea surface temperatures (SSTs) >15°C near the KE meander probably because of their poor tolerance to lower temperatures and limited swimming ability. Squid of 10–15 cm ML were distributed in the offshore waters of 10–15°C SST and in the coastal waters of northern Honshu, and underwent diel vertical migrations between the sea surface at night and deeper layers during the daytime. Squid larger than 15 cm ML were distributed in the coastal feeding grounds of northern Honshu and Hokkaido until they began their southward spawning migration. They also underwent diel vertical migrations, but remained deeper at night than the squid of 10–15 cm ML; this migration pattern closely matched that of their main prey such as euphausiids. We concluded that as T. pacificus grow, they shift their distribution range from the temperate surface layer around the KE toward the colder deeper layers, above 5°C, in the Oyashio and coastal areas.