THE RESPONSE OF TOBACCO TO SEEDBED APPLICATION OF DIPHENAMID

Summary. Seeds of three tobacco Nicotiana tabacum L.) varieties were soaked in water for 0, 1, 3 or 5 days and treated, after sowing in glasshouse flats, with NN -dimethyl-αα-diphenylacetamide (diphenamid) at 4·5 kg/ha 1, 3 or 5 days after sowing or at the cotyledonary stage. Unsprayed series were included as controls. Diphenamid caused thinning of seedlings in all varieties, but one (Maryland Catterton) showed some tolerance. All varieties showed stunting and malformations from diphenamid, particularly when seeds soaked for 5 days were treated either 1 or 5 days after sowing.     

Deformation of (Mg,Fe)SiO3 post-perovskite and D' anisotropy

Polycrystalline (Mg(0.9),Fe(0.1))SiO3 post-perovskite was plastically deformed in the diamond anvil cell between 145 and 157 gigapascals. The lattice-preferred orientations obtained in the sample suggest that slip on planes near (100) and (110) dominate plastic deformation under these conditions. Assuming similar behavior at lower mantle conditions, we simulated plastic strains and the contribution of post-perovskite to anisotropy in the D' region at the Earth core-mantle boundary using numerical convection and viscoplastic polycrystal plasticity models. We find a significant depth dependence of the anisotropy that only develops near and beyond the turning point of a downwelling slab. Our calculated anisotropies are strongly dependent on the choice of elastic moduli and remain hard to reconcile with seismic observations.     

Trypanosome genetics: populations, phenotypes and diversity

In the last decade, there has been a wide range of studies using a series of molecular markers to investigate the genotypic diversity of some of the important species of African trypanosomes. Here, we review this work and provide an update of our current understanding of the mechanisms that generate this diversity based on population genetic analysis. In parallel with field based studies, our knowledge of the key features of the system of genetic exchange in Trypanosoma brucei, based on laboratory analysis, has reached the point at which this system can be used as a tool to determine the genetic basis of a phenotype. In this context, we have outlined our current knowledge of the basis for phenotypic variation among strains of trypanosomes, and highlight that this is a relatively under researched area, except for work on drug resistance. There is clear evidence for ‘strain’-specific variation in tsetse transmission, a range of virulence/pathogenesis phenotypes and the ability to cross the blood brain barrier. The potential for using genetic analysis to dissect these phenotypes is illustrated by the recent work defining a locus determining organomegaly for T. brucei. When these results are considered in relation to the body of research on the variability of the host response to infection, it is clear that there is a need to integrate the study of host and parasite diversity in relation to understanding infection outcome.     

Isolation in cell cultures and initial characterisation of two novel bocavirus species from swine in Northern Ireland

We report the isolation in cell cultures of two novel bocavirus species in pigs from farms in Northern Ireland with clinical postweaning multisystemic wasting syndrome (PMWS). We have designated the isolates as porcine bocavirus-3 (PBoV3) and porcine bocavirus-4 (PBoV4). To date 5082 and 4125 bps of PBoV3 and PBoV4 have been sequenced, respectively. PBoV3 and PBoV4 show nucleotide homology to other known bocaviruses in swine and other organisms. Open reading frame (ORF) analysis has shown that these viruses have a third small ORF, equivalent to the NP1 ORF that distinguishes the bocaviruses from other parvoviruses. A panel of porcine field sera was screened by indirect immunofluorescence against both viruses. Of the 369 samples analysed, 32 (8.7%) and 35 (9.5%) sera were seropositive for PBoV3 and PBoV4 respectively, thus providing serological evidence of the exposure of swine in the field to bocavirus-like viruses. To date, the clinico-pathological significance of these novel swine bocaviruses, as primary pathogens or as immunosuppresive triggers for other infectious agents, is undetermined.     

Genetic diversity in the 3' terminal 4.7-kb region of grapevine leafroll-associated virus 3

Grapevine leafroll-associated virus 3 (GLRaV-3; Ampelovirus, Closteroviridae), associated with grapevine leafroll disease, is an important pathogen found across all major grape-growing regions of the world. The genetic diversity of GLRaV-3 in Napa Valley, CA, was studied by sequencing 4.7 kb in the 3' terminal region of 50 isolates obtained from Vitis vinifera 'Merlot'. GLRaV-3 isolates were subdivided into four distinct phylogenetic clades. No evidence of positive selection was observed in the data set, although neutral selection (ratio of nonsynonymous to synonymous substitution rates = 1.1) was observed in one open reading frame (ORF 11, p4). Additionally, the four clades had variable degrees of overall nucleotide diversity. Moreover, no geographical structure among isolates was observed, and isolates belonging to different phylogenetic clades were found in distinct vineyards, with one exception. Considered with the evidence of purifying selection (i.e., against deleterious mutations), these data indicate that the population of GLRaV-3 in Napa Valley is not expanding and its effective population size is not increasing. Furthermore, research on the biological characterization of GLRaV-3 strains might provide valuable insights on the biology of this species that may have epidemiological relevance.     

Interplanetary Magnetic Field Polarity and the Size of Low-Pressure Troughs Near 180{degrees}W Longitude

When the interplanetary magnetic field is directed away from the sun, the area of wintertime low-pressure (300-millibar) troughs near 180 degrees W longitude is significantly larger than when the field is toward the sun. This relation persists during most of the winters of 1951 to 1973.