Alternative sampling to establish the Escherichia coli O157 status on beef cattle farms

Prevalence of Escherichia coli O157 in cattle at the farm level is mostly determined by taking individually rectal samples. From the animal welfare point of view the collection of such samples on the farm is not advisable. The present study evaluated alternative sample types to assess the E. coli O157 status of cattle farms. Twelve closed cattle farms were visited twice with a time interval of 6-8 months. Rectal and hide surface samples (the nose, the neck, the shoulder, the flank, and the round) were collected from beef cattle within the period of 5 months before slaughter and from their environment (overshoes from the pen bedding, swabs from the pen barrier, feed and water). Statistical analysis revealed that from all samples taken only the "overshoe method" might be a good sampling technique to substitute the collection of individual fecal samples to establish the E. coli O157 status of a farm and even a pen. Characterization of the isolates, using pulsed field gel electrophoresis, revealed that on each positive farm only one genotype was presented, even after a period of more than 6 months.     

Interspecific hybridisation between Hibiscus syriacus, Hibiscus sinosyriacus and Hibiscus paramutabilis

Interspecific hybrids from crosses between H. syriacus × H. paramutabilis and H. syriacus × H. sinosyriacus were obtained. In both cases unilateral incongruity was observed and reciprocal crosses yielded no fruits. In vitro embryo rescue, 11 weeks after pollination, increased the germination capacity of H. syriacus × H. sinosyriacus embryos, while this was not the case for H. syriacus × H. paramutabilis embryos. However, a lot of the generated H. syriacus × H. sinosyriacus seedlings were lost due to variegated and total albinism. In the progeny of H. syriacus ‘Oiseau Bleu’ × H. paramutabilis about 95% of the seedlings had an intermediate flower and leaf morphology compared to both parent plants. Leaves on the adult F1 hybrids showed a polymorphism. In total four different leaf types could be observed on the same plant. This leaf polymorphism also was seen in the progeny of H. syriacus ‘Melwhite’ × H. sinosyriacus ‘Lilac Queen’. In this progeny about 50% of the seedlings had an intermediate flower and leaf morphology compared with the parent plants. The hybrid nature of the seedlings of both progenies was also confirmed by AFLP analysis. Despite the low germination vigour of the pollen of the hybrids, a small F2 generation was obtained from H. syriacus ‘Oiseau Bleu’ × H. paramutabilis.     

Interspecific hybridization in <Emphasis Type="Italic">Sarcococca</Emphasis> supported by analysis of ploidy level,genome size and genetic relationships

Knowledge of ploidy level differences, genome size and genetic relationships between species facilitates interspecific hybridization in ornamentals. For Sarcococca (Buxaceae) only limited (cyto)genetic information is available. The aim of this study was to determine the genome size and chromosome number and to unravel the genetic relationships of a breeder’s collection using AFLP marker analysis. Based on these results, interspecific crosses were made and the efficiency and hybrid status was verified. Two groups of diploid plants (2n = 2x = 24) were observed, with either a genome size of 4.11–4.20 or 7.25–9.63 pg/2C. All the tetraploid genotypes (2n = 4x = 48) had genome sizes ranging from 7.91 to 8.18 pg/2C. In crosses between parents with equal ploidy level and genome size a higher crossing efficiency (on average 58% of the hybridizations resulting in fruits) and more true hybrids (on average 96% of the offspring) were obtained compared to crosses between plants with different genome size and ploidy level (on average 23% fruits and 24% hybrids, respectively). In none of the cross combinations, the ploidy level or genome size was found to be a complete hybridization barrier, although unilateral incongruity was found in some cross combinations. Distant genetic relationships did not hamper the hybridization within Sarcococca genotypes. Our findings will contribute to a more efficient breeding program and a faster achievement of hybrids with an added value.     

Interspecific hybridisation and genome size analysis in <Emphasis Type="Italic">Buddleja</Emphasis>

Interspecific hybrids Buddleja davidii × Buddleja weyeriana, Buddleja weyeriana × Buddleja davidii and Buddleja davidii × Buddleja lindleyana were generated using in vitro embryo rescue 10–11 weeks after manual pollination. The morphological variation within the F1 populations was limited. The F1 progeny of B. davidii × B. lindleyana was almost sterile and no F2 generation was obtained. From the other hybrids, F2 generations were made by self pollinations and back crosses. Hybrid nature of all F1 and F2 seedlings was confirmed by AFLP. Chromosome counting and genome size measurement for B. weyeriana (F2 selection of (diploid) B. globosa × (tetraploid) B. davidii) revealed a higher chromosome number (76 chromosomes) and genome size than expected, indicating 2n-gametes formation occurred during meiosis of B. globosa. The F1 hybrids B. weyeriana × B. davidii (76 chromosomes) had an intermediate genome size compared with the genome size of the parent plants, proving their hybrid nature. However, the F1 and F2 hybrids of B. davidii × B. weyeriana all had 76 chromosomes but had a lower genome size than expected, suggesting the occurrence of chromosome rearrangements in the genome of the hybrids. B. lindleyana had 38 chromosomes, while the F1 hybrids of B. davidii × B. lindleyana had 76 chromosomes. Also genome size measurements revealed that the F1 seedlings B. davidii × B. lindleyana had higher genome sizes than expected. Both the results of chromosome counting and genome size measurement indicate that 2n-gametes formation took place during meiosis of B. lindleyana.     

Effects on pesticide spray drift of the physicochemical properties of the spray liquid

This research was on the effect of the physicochemical properties of the spray liquid on pesticide spray drift. Ten pesticide spray liquids with various physicochemical properties were selected for study. Some of these spray liquids were also examined with the addition of a polymer drift-retardant. In the first part, laboratory tests were performed to measure surface tension, viscosity, evaporation rate and density of the spray liquids. Subsequently, drift experiments were performed in a wind tunnel. From the results it was found that the dynamic surface tension is a major drift-determining factor, and also that the addition of a polymer drift-retardant can reduce drift significantly by increasing the viscosity. Drift reduction was found to be less effective with spray liquids of emulsifiable and suspendable formulation types than with spray liquids of water-dispersible granules and powders.     

Occurrence of non-sorbitol fermenting, verocytotoxin-lacking Escherichia coli O157 on cattle farms

Escherichia coli O157 is often associated with hemorrhagic colitis and the hemolytic uremic syndrome (HUS). The verocytotoxins are considered to be the major virulence determinants. However, vt-negative E. coli O157 were recently isolated from patients with HUS. Several transmission routes to humans are described, but cattle feces are the primary source from which both the food supply and the environment become contaminated with E. coli O157.In a prevalence study performed on dairy, beef, mixed dairy/beef and veal farms in the summer of 2007, vt-negative isolates were detected on 11.8% (8/68) of the positive farms. From these eight farms, a total of 43 sorbitol-negative E. coli O157:H7 were collected. On five farms, only strains negative for the vt genes were present whereas both vt-negative and vt-positive strains could be detected on three other farms. Further characterization revealed that all isolates carried the eaeA and hlyA genes. Pulsed-field gel electrophoresis (PFGE) of all isolates resulted in nine different PFGE types and within the vt-negative strains, four different genotypes were identified, indicating that certain genetic clones are widespread over the cattle population.