The use of incidence counts for estimation of cereal aphid populations. 3. Population development and the incidencedensity relation

The relation between the population density of the cereal aphid,Sitobion avenae, and the proportion of wheat tillers infested is examined. Three of the six models considered require the assumption that the aphids' spatial configuration can be described by a single statistical distribution; as this is not true forS. avenae these models are unsuitable. When the other three models were applied to field sample data, only that of Nachman (1981) yielded a regression equation that remained constant throughout the development of the aphid population.Samenvatting Om in de praktijk gebruik te kunnen maken van incidentie (de fractie bezette halmen) voor het schatten van graanluispopulaties moet dezelfde relatie tussen dichtheid en incidentie tijdens het hele groeiseizoen gelden. Uit analyses van veldgegevens voor de graanluisSitobion avenae blijkt dat wel het geval te zijn, zodat bepalingen van incidentie kunnen worden gebruikt om de populatiedichtheid betrouwbaar te schatten.     

Characterization of Distinct Tombusviruses that Cause Diseases of Lettuce and Tomato in the Western United States

A soilborne disease of lettuce, associated with necrosis and dieback, has been found with increasing frequency in California and Arizona over the last 10 years. An isometric virus, serologically related to Tomato bushy stunt virus (TBSV), was consistently isolated from lettuce plants with these disease symptoms. Back-inoculation to healthy lettuce plants and subsequent reisolation of the virus from symptomatic lettuce leaves suggested that this virus was the causal agent of this disease. A tombusvirus was also associated with a necrosis disease of greenhouse-grown tomatoes in Colorado and New Mexico. Complementary DNA representing the 3' end of viral genomic RNAs recovered from diseased lettuce and tomato plants had identical nucleotide sequences. However, these sequences were divergent (12.2 to 17.1%) from sequences of the previously described strains of TBSV, Petunia asteroid mosaic virus (PAMV), Artichoke mottled crinkle virus, and Carnation Italian ringspot virus. Additional tombusvirus isolates were recovered from diseased lettuce and tomato plants and these were most closely related to the TBSV-cherry strain (synonymous with PAMV) and to Cucumber necrosis virus based on comparison of 3'-end sequences (0.1 to 0.6% and 4.8 to 5.1% divergence, respectively). Western blot analysis revealed that the new tombusvirus isolated from diseased lettuce and tomato plants in the western United States is serologically distinct from previously described tombusvirus species and strains. Based on genomic and serological properties, we propose to classify this virus as a new tombusvirus species and name it Lettuce necrotic stunt virus.     

Improving Drought Tolerance of Rice by Designed QTL Pyramiding

Drought is the most important factor limiting rice yields in the rainfed areas of Asia. To overcome the problem, we developed a new strategy ＇designed QTL pyramiding＇ to more efficiently develop drought tolerant （DT） rice cultivars. In the first phase of this strategy, we developed large numbers of introgression lines （ILs） in elite backgrounds using backcross （BC） breeding, each of which carries multiple genomic segments for improved DT from a known donor. Then, we genotyped all ILs with SSR markers to track the genomewide pattern of introgression in the DT ILs of 16 BC populations derived from crosses between 2 recipients （IR64 and Teqing） and four different donors. X^2 tests and linkage disequilibrium analyses of introgression in the DT ILs revealed significant frequency shifts at many loci across the genome and non-random associations at the multilocus level as a result of selection for DT in the ILs, which led us to the discovery of putative genetic networks underlying DT in the ILs. The networks each containing all DT loci detected in ILs from a BC population showed some interesting features.     

Sperm production and quality in European eel (Anguilla anguilla) in relation to hormonal treatment

Aquaculture production relies on controlled management of gametogenesis, especially in species where assisted reproduction is needed for obtaining gametes in captivity. The present study used human chorionic gonadotropin (hCG) treatments to induce and sustain spermatogenesis in European eel (Anguilla anguilla). The aim was to evaluate effects of strip-spawning timing (12 vs. 24 hr) after weekly administration of hCG and the necessity of a primer dose (in addition to weekly hormonal treatment) prior to strip spawning (primer vs. no-primer) on sperm quality parameters. Sperm parameters included milt production (weight), density and sperm kinematics at Week 9, 11 and 13 after onset of treatment. Spermiation commenced in 11.5% of males in Week 5 and by Week 9, and all males produced milt. Male weight, milt production, sperm density and spermatocrit did not differ among hormonal treatments during the experimental period. Overall, male weight decreased from 106.3 to 93.0 g, milt weight increased from 3.5 to 5.4 g, sperm density counts decreased from 11.7 × 10⁹ to 10.5 × 10⁹ cells/ml, and spermatocrit decreased from 46.5% to 40.5%. Furthermore, spermatocrit was positively related to haemocytometer counts (R² = .86, p < .001), providing a reliable indicator of sperm density. Differences in sperm kinematics were observed depending on strip-spawning timing after hormonal injection (12 vs. 24 hr) but with no consistent pattern. These sperm quality parameters also did not consistently differ between the no-primer and primer treatments. Considering that each male may be stripped 4–5 times over the 2–3 months spawning season, omitting the primer would reduce animal handling, material costs and labour intensity, while sustaining high-quality sperm production.     

Coal science: basic research opportunities

More fundamental knowledge of coal (knowledge of its structure and its behavior during conversion processes) is essential before we can generate new technologies necessary for the efficient use of coal in the future. Herein are suggested specific basic research opportunities in the areas of coal characterization, gasification, combustion, and liquefaction, along with an assessment of the impact such research programs could have. Critical characterization needs include qualitative and quantitative determination of the chemical forms of carbon, oxygen, nitrogen, and sulfur and reliable methods for the measurement of surface area, pore volume, and weight-average molecular weights. Mechanistic studies aimed at increasing understanding of the thermal breakdown of the functionalities in coal, the behavior of coal in the presence of molecular and donor hydrogen environments, and carbon gasification and hydrocarbon synthesis reactions starting from carbon monoxide and hydrogen will lay the scientific foundation for the development of new processes for converting coal into clean usable fuels and chemicals.