Mobility and degradation of the herbicide imazosulfuron in lysimeters under field conditions

The mobility and degradation of imazosulfuron, labeled with carbon-14 at the imidazole ([imi-(14)C]imazo) or pyrimidine ring ([pyr-(14)C]imazo), in lysimeters with 1 m(2) surface and 110 cm depth were investigated for three years. One lysimeter was treated with [imi-(14)C]imazo in two successive years at the rate of 50 g of active ingredient (ai)/ha each. The other two lysimeters were treated once with [pyr-(14)C]imazo and a mixture (1:1, w/w) of the two labeled imazosulfurons, respectively (50 g of ai/ha). In the first and second years of monitoring, the yearly mean concentration of (14)C in the leachate water was <0.10 microg/L in each lysimeter. Although in the third year the concentration of (14)C in the leachate water was 0.17 microg/L for the lysimeter treated twice with [imi-(14)C]imazo, the concentration of imazosulfuron and its degradation products in the leachate water ranged from 0.01 to 0.06 microg/L. At the study termination, the main portion of (14)C recovered was found in the upper 30 cm soil layer in each lysimeter, and no (14)C was detected below a depth of 50 cm. These findings indicated that imazosulfuron and its degradation products in soils translocated into groundwater only slightly.     

Role of coresistance in the development of resistance to chloramphenicol in Escherichia coli isolated from sick cattle and pigs

OBJECTIVE: To determine the cause of persistent resistance to chloramphenicol (CP) after the ban on its use in food-producing animals in several countries. SAMPLE POPULATION: 71 CP-resistant and 104 CP-susceptible Escherichia coli strains isolated from sick cattle and pigs in Japan. PROCEDURE: Susceptibility of all bacterial strains to thiamphenicol (TP) and florfenicol (FFC) was tested by use of an agar dilution method. The CP-resistance genes and variable region within class 1 integrons in CP-resistant strains were identified by use of a PCR assay. RESULTS: The CP acetyltransferase gene (ie, cat1) was identified as the predominant CP-resistance gene in strains isolated from cattle, and the cat1and nonenzymatic CP-resistance gene (ie, cmlA) were the predominant CP-resistance genes in strains isolated from pigs. Additionally, strains with cat1 isolated from cattle often were resistant to ampicillin, dihydrostreptomycin (DSM), oxytetracycline, and trimethoprim (TMP), whereas strains with cat1 or cmlA isolated from pigs often were resistant to DSM and TMP. Class 1 integrons were significantly more prevalent in strains with CP-resistance genes, compared with prevalence in strains without CP-resistance genes. All gene cassettes within the integrons were involved in resistance to DSM, TMP, or both. CONCLUSIONS AND CLINICAL RELEVANCE: Coresistance that develops because of the use of DSM and TMP in cattle and pigs apparently contributes to the selection of CP-resistant strains of E coli. Thus, it is possible that bacterial resistance to CP in animals would persist despite a ban on the use of CP in cattle and pigs.     

Progress in varietal improvement for increasing upland rice productivity in the tropics

Enhancing rice yield in upland rice systems through genetic improvement remains a major challenge in the tropics. This review aims to provide the trends on upland rice cultivation over the last 30 years and recent distribution of upland rice in the tropics, and to report progress in studies on genetic improvement for enhancing productivity in Africa, Asia, and Latin America. While upland rice cultivation area has reduced in Asia and Latin America over the last 30 years, the area in Africa has increased. The current share of upland rice area in total rice area is related to rainfall and gross national income per capita, especially in Africa, and higher share is associated with lower rice self-sufficiency at national level. Breeding programs in Asia and Latin America have developed high-yielding varieties using indica materials as parents. In Africa, New Rice for Africa (NERICA) varieties were developed from crosses between improved tropical japonica and Oryza glaberrima. However, recent studies report that there is scope for improving existing NERICA using upland indica materials from Asia. In highlands of Africa, there are ongoing breeding programs using japonica varieties, such as the Nepalese Chhomrong Dhan. Key important plant traits used in the breeding programs are not largely different across regions, especially intermediate plant height and tillering capacity (which may be related to weed-suppressive ability), and high harvest index. In conclusion, we propose an international network for breeding upland rice with accelerating seed exchange across regions that could enhance upland rice productivity through genetic improvement.     

Fractionation of phosphorus in soils with different geological and soil physicochemical properties in southern Tanzania

ABSTRACT

Soil phosphorus (P) forms have been practically defined as chemically fractionated pools. A knowledge of the abundance and diversity of P forms in soil, and the factors affecting them, will lead to better soil management. However, little is known about the differences in P forms among soils with different geological properties in tropical Africa. The aim of this study was to investigate the P forms in soils with different physicochemical properties formed under different geological conditions in southern Tanzania and to identify the factors affecting the P forms in these soils. In total, 37 surface soil samples were collected from three geological groups; the plutonic (mainly granite) rock (PL) group, the sedimentary and metamorphic rock (SM) group, and the volcanic ash (V) group. Soil P was sequentially extracted by NH₄Cl, NH₄F, NaHCO₃, NaOH + NaCl, and HCl, and inorganic (P_i) and organic P (P_o) in each fraction were determined. The lowest total P was in the PL group (average, 360 mg P kg^-1) because of the high sand content. Iron (Fe)-P (NaOH-P_i) was the major form in this group, accounting for 8.4% of total P. In the SM group (average total P, 860 mg P kg^-1), Fe-P was the major form in most, accounting for 7.8% of total P. Soils in the SM group occasionally had high calcium (Ca)-P due to application of chemical fertilizer at the collection site. The V group had the highest total P (average, 1600 mg P kg^-1) and its major P form was Ca-P, which was possibly derived from primary minerals (i.e., apatite), accounting for 14% of total P. In addition, the high oxalate-extractable Al possibly caused the accumulation of Al-P in the V group. Oxalate-extractable Fe generally increased with increasing Fe-P_i, while oxalate-extractable Al increased with increasing organic P and Al-P_i in soils in all three geological groups. These results demonstrate that the soil P forms differ greatly among sites in southern Tanzania with different geological conditions and associated soil properties.     

Novel reovirus isolation from an Ostrich (Struthio camelus) in Japan

An orthoreovirus was isolated from an Ostrich (Struthio camelus) and rapidly identified as orthoreovirus by the rapid determination of viral RNA sequences (RDV) system and electron microscopy. Phylogenetic analysis of the sigma A protein indicated that the isolate belonged to avian species and was closely related to chicken orthoreovirus strain 138. The results of the present study indicated that an ostrich orthoreovirus is slight different from other chicken orthoreoviruses and provided evidence of diversity among avian orthoreoviruses. To our knowledge, this is the first genetic report of an orthoreovirus isolated from an ostrich.