Enzymatic Maceration of Witloof Chicory by the Soft Rot Bacteria Erwinia carotovora Subsp. carotovora: The Effect of Nitrogen and Calcium Treatments of the Plant on Pectic Enzyme Production and Disease Development

Disease incidence of bacterial soft rot caused by Erwinia carotovora subsp. carotovora and activities of bacterial pectolytic enzymes were studied in witloof chicory. Disease incidence after forcing of the chicory heads was enhanced by the nitrogen treatment and reduced by the calcium treatment of the chicory plants prior to forcing. Significant differences in susceptibility to bacterial soft rot were found for the tested chicory cultivars. Disease severity after 96h ranged from 6% in Clause R2 to 100% in Bea and Tabor. Chicory cultivars Rumba and Salsa showed a final average severity of 65–70%. Activity of the pectolytic enzymes, polygalacturonase and pectate lyase increased in artificially inoculated chicory heads of cultivar Rumba and was not affected by calcium and nitrogen treatments of the plants. Polygalacturonase showed highest activity 48h after inoculation while pectate lyase activity increased throughout 72h of incubation. Maceration of the chicory tissue and bacterial growth increased continuously until 96h after inoculation, when more than 60% of the chicory heads was macerated by pectolytic enzymes of the bacteria. Enzyme activity of Erwinia carotovora subsp. carotovora grown on chicory cell wall extracts was influenced by nitrogen and calcium treatments of the chicory plants. The activity of polygalacturonase reached its highest level at 48h after incubation and pectate lyase activity peaked at 24h followed by a continuous decrease until 72h after inoculation.     

Production, disinfection and evaluation for aquaculture applications of rotifer resting eggs from Bohai Bay, P.R. of China

The dynamics of resting egg production of the rotifer Brachionus plicatilis originating from a wild population in the Tanggu Saltworks (P.R. China) was investigated. In the natural environment as well as in semi-controlled rearing conditions an increased resting egg production was noticed with declining food availability. Processed resting eggs had a hatching efficiency of 3 x 10 6 rotifers per gramme irrespective of their origin. Hatching started 22 h after the initiation of incubation and was completed after 36 h. Rotifers obtained from resting eggs could be further cultured on Culture Selco® and enriched with Super Selco®. The fatty acid profile of these rotifers were not divergent from reference rotifers (originating from the Laboratory of Aquaculture and Artemia Reference Centre) demonstrating that this strain was not catabolizing essential fatty acids and could be used for enrichment purposes. Storage of resting eggs at 4°C resulted in a 50% lower hatching after 1 year but remained stable during the next 2 years. The resting eggs used for storage could easily be disinfected without affecting their hatching characteristics. These results indicate that this material could be used as inocula for mass cultures of live food for commercial hatcheries.     

Soil dynamics of the origination of soil tare during sugar beet lifting

High soil tare of sugar beet on wet clay soil after uprooting with share lifters is usually attributed to the fact that the soil becomes sticky due to mechanical impact during uprooting. Results of field experiments have shown good potential for obtaining low soil tare of sugar beet on wet clay soil by beet extraction with a high average vertical acceleration and a spiral extraction path with a small pitch. The objective of this research was to provide models for soil–beet–lifter systems used in these experiments, and to simulate some of the observed effects of the uprooting method on soil tare and soil adherence. As the rootlet system plays an important role in the origination of soil tare, the rootlet system was also modelled. A constitutive soil model, assuming elastic–perfectly-plastic soil behaviour, was used as a basis for modelling soil–beet–lifter system variants, including beet with and without rootlets, uprooting by extraction, rotation and extrusion, and uprooting with low and high vertical acceleration. The origination of soil tare is presented on the basis of the calculated zone of initial soil failure during extraction. Expected soil adherence is discussed in relation to the stress state of the soil. The simulated initial soil failure and stress state of the soil agreed well with experimental results on soil tare and soil adherence.     

Total CK and CK-BB activity in serum from sheep with scrapie.

Total CK and iso-enzyme CK-BB activity was measured in serum from four sheep with scrapie and in serum from four healthy control sheep. Blood samples were taken weekly for about six months. There was a clear overlap between the total CK and CK-BB activity in serum from sheep with scrapie and that in serum from control sheep. Thus measurement of these enzymes does not aid the clinical diagnosis of scrapie.     

Isolation of Cowdria ruminantium by means of Percoll density gradient centrifugation and detection by an enzyme-linked immunosorbent assay

The isolation of Cowdria ruminantium by means of Percoll density gradient centrifugation permits the recovery of partially purified viable populations of the organism possessing distinctly different densities. These conclusions are based upon results of analyses of density fractions by intravenous inoculation into sheep, protein determination, electron microscopy and enzyme-linked immunosorbent assay. Morphological differences were observed in the density fractions obtained from infected brain tissue and Amblyomma hebraeum nymphae.     

The detection of antibodies to Cowdria ruminantium in serum and C. ruminantium antigen in Amblyomma hebraeum by an enzyme-linked immunosorbent assay

A sensitive and reliable enzyme-linked immunosorbent assay for the detection of antibodies to Cowdria ruminantium in serum and C. ruminantium antigen in Amblyomma hebraeum nymphae is described. For the screening of antibodies, C. ruminantium from A. hebraeum nymphae, partially purified by wheat-germ lectin affinity chromatography, was used as antigen. To screen nymph populations, sera from either Ball 3 strain-infected sheep or Kumm-strain infected mice were used. By using appropriate controls the assays were rendered specific with respect to C. ruminantium.     

Production of virus-free freesia's by means of meristem culture

Samenvatting Door middel van meristeemcultures werd getracht virusvrije planten te verkrijgen van vijf Freesia-variëteiten. Hiertoe werden meristemen uitgeprepareerd en op verschillende voedingsbodems geplaatst (Fig. 1). Op één medium ontwikkelde zich een aantal meristemen tot normale planten, op de andere media vertoonden de cultures soms een overmatige wortelontwikkeling. Veertien meristemen groeiden uit tot planten (Tabel 1, Fig. 2), waarvan na serologische toetsing er zes virusvrij bleken te zijn.The authors thank MissW. M. Haen for technical assistance.     

Numbers of dogs, cats, birds, and exotic animals in veterinary practices in the Netherlands 1994-2005 and possible consequences for the veterinary curriculum

The species of pets owned in the Netherlands are constantly changing, and it is important that veterinary practitioners have information about the number and species of pets presented in veterinary practice. Using the same methodology as in 1994, we determined the relative importance of the various pet species in 2005 and compared these data with those for 1994. The most notable findings were a 25% increase in the number of birds and exotic animals seen in small and large animal practices (from about 10% to about 12.5%), a doubling of the number of birds and tripling of the number of pigeons seen in mixed practices, a doubling of the number of reptiles seen in small animal practices, and a 10-fold increase in the number of fish seen in veterinary practices in general. There was a significant decrease in the proportion of cats (from 46% to 40.7%) and an increase in the proportion of dogs (from 44% to 46.7%). These trends in veterinary practice consultations did not parallel those seen in pet ownership. The increase in the number of birds (especially pigeons), reptiles, and fish seen in veterinary practice emphasizes the need to pay attention to these species in the standard companion animal curriculum.     

Detection of downy and powdery mildew resistance QTL in a ‘Regent’ × ‘RedGlobe’ population

One hundred and eighty six F₁ plants from a ‘Regent’ × ‘RedGlobe’ cross were used to generate a partial linkage map with 139 microsatellite markers spanning all 19 chromosomes. Phenotypic scores for downy mildew, taken over two years, confirmed a major resistance QTL (Rpv3) against downy mildew in the interval VVIN16-cjvh to UDV108 on chromosome 18 of ‘Regent’. This locus explained up to 62 % of the phenotypic variance observed. Additionally a putative minor downy mildew resistance locus was observed on chromosome 1 in one season. A major resistance locus against powdery mildew (Ren3) was also identified on chromosome 15 of ‘Regent’ in the interval UDV116 to VChr15CenGen06. This study established the efficacy of and validated the ‘Regent’-derived downy and powdery mildew major resistance genes/QTL under South African conditions. Closely linked SSR markers for marker-assisted selection and gene pyramiding strategies were identified.