Serology of Haemophilus (Actinobacillus) pleuropneumoniae serotype 5 strains: establishment of subtypes a and b

The serological characteristicis of 14 strains assigned to serotype 5 were examined by the slide agglutination test, the indirect haemagglutination (IHA) test and by gel diffusion.All the strains possessed identical capsular antigenic determinants of polysaccharide (PS) nature and lipopolysaccharide (LPS) nature. However, based upon a capsular antigenic determinant of PS nature the strains could be divided in two subtypes. It is therefore proposed to refer to the H. pleuropneumoniae strains of serotype 5 to two subtypes: subtype a with strain K17 as the subtype strain and subtype b with strain L20 as the subtype strain.     

Identification of dynamic growth of Hedera helix as response to variation in daily light levels

Summary

The dynamic responses in shoot growth of three pot plants ofHedera helix L. ‘Mein Herz‘ in relation to changes in photosynthetic photon flux density (PPFD) is identified. In the experiment a two-level strategy of PPFD to the plants was used. The current level of PPFD on any day was either high or low, and was determined using a pseudo random binary signal (PRBS) both to avoid any correlations between the PPFD and other variables, and to ensure that the dynamic characteristics of the plant growth were present in the data. For each of the three pot plants a discrete dynamic model of growth responses to PPFD was estimated, and an agreement between the parameters of the three models was observed. The results show that not only is the current PPFD level of the current day related to the daily increase in fresh weight, but growth is also a function of the PPFD level of the previous days. With respect to the previous days the effects of PPFD can be described as an exponential decay where from one day to the previous day the effect of PPFD is reduced to 67%, 66% and 80% respectively for the three pot plants in the experiment.     

Propagation temperature,PPFD, auxin treatment,cutting size and cutting position affect root formation,axillary bud growth and shoot development in miniature rose (Rosa hybrida L.) plants and alter homogeneity

Summary

Rooting and growth responses of miniature rose cuttings were investigated in an experiment in which four propagation temperatures, two photosynthetic photon flux densities (PPFDs) with five auxin (IBA) concentrations, cutting sizes and cutting positions, were combined factorially in a response-surface design. Most prominently, temperature, cutting size and auxin and their interactions, influenced root and shoot growth. A propagation temperature of 24.6°C, and IBA concentrations between 10^–3 and 10^–1M, depending on temperature, were optimal for root formation. Root formation in extra short cuttings was delayed at low IBA concentrations. Regarding root formation, IBA could substitute for increased temperature as well as for increased cutting size. Onset of axillary bud growth was fastest at 24.6°C, and delayed in extra short cuttings. Application of IBA at 10^–4 to 10^–3M was optimal for axillary bud growth. By increasing the IBA concentration both time to flowering and plant height increased at 24.6°C. In cuttings from higher positions on stock plants, axillary shoots enhanced their growth to flowering, became shorter, and weighed less, suggesting occurrence of positional effects (topophysis). The growth rate increased with increasing IBA concentration, as well as from medial to low positioned cuttings. Increasing propagation PPFD from 46 to 72 µmol m^–2s^–1 did not affect the parameters. Time to axillary bud growth and time to first flower were related to time-to-visible root. Fast formation of roots apparently resulted in fast axillary bud growth. In time-to-visible root and axillary bud growth, the smallest variation between plants was found at optimal ranges for temperature, IBA concentration and cutting size, and further factors optimal for root formation and axillary bud growth provided the most synchronized plant development.     

Controlled atmosphere storage at high CO2 and low O2 levels affects stomatal conductance and influence root formation in kalanchoe cuttings

Since the response of cuttings to raised CO₂ concentration is not documented, controlled atmosphere (CA) storage of kalanchoe cuttings at combinations of high carbon dioxide and low oxygen levels was investigated to study the feasibility of using CA to sustain quality of cuttings prior to planting. During storage, stomata opening and plant fresh weight (FW) were measured, and root formation (RF) was recorded post storage. Storage atmosphere composition (10/2, 15/2, or 15/5; kPa CO₂/kPa O₂), storage duration (9 or 19 days), and cutting type (rooted or un-rooted) affected stomata conductance (G_s), and influenced FW and subsequent RF in cuttings of kalanchoe ‘Yellow Josefine’. In CA stored plants, G_s was high, 60–160 mmol m⁻² s⁻¹, indicating open stomata, whereas in control plants G_s was low, 5–14 mmol m⁻² s⁻¹, indicating closed stomata. Generally G_s values were higher for un-rooted than for rooted cuttings. Overall, cutting FW was reduced by CA storage with no significant differences in FW reduction between the CA treatments. RF of un-rooted CA stored cuttings was comparable to that of controls, whereas for rooted cuttings controls grew better than CA stored cuttings. CA at 10 kPa CO₂ and 2 kPa O₂ for 2–3 weeks could sustain un-rooted cuttings, in a pests-free state whilst retaining the ability of the cuttings RF. The results showed that stomata aperture may be altered by high CO₂ concentration combined with low O₂, and results indicated that this effect was not only caused by high CO₂ but also by low O₂ concentration. In addition, the results indicated that CA storage, stomata conductance, and water stress of kalanchoe cuttings may be correlated. Monitoring G_s of leaves of cuttings could be used as a non-destructive indicator of storability and quality status. Based on the novel positive preliminary results reported here, a protocol that focuses on minimising water loss should be developed and optimised for kalanchoe.     

Relative absorption of fatty acids by Atlantic salmon Salmo salar from different diets,as evaluated by multivariate statistics

By using a rapid and simple chemometric method it was shown that Atlantic salmon Salmo salar absorbed the polyunsaturated fatty acids from highly unsaturated diets more efficiently than the monounsaturated and saturated fatty acids. For the monounsaturated and the saturated fatty acids, the degree of absorption decreased with increasing chain length. The diets, based on oils from five different commercial fish species, had different fatty acid profiles. The differences between the several diet groups were maintained between the corresponding faeces groups, even though the fatty acid composition of the faeces was very different from that of the diet. This was because the proportion which was absorbed of each fatty acid was almost equal for all diets.     

Genetic variation in Norwegian piscine myocarditis virus in Atlantic salmon,Salmo salar L.

Cardiomyopathy syndrome (CMS) in Atlantic salmon, Salmo salar L., is a severe cardiac disease characterized by a necrotizing myocarditis involving the atrium and the spongious part of the ventricle. The disease is caused by piscine myocarditis virus (PMCV), a double‐stranded RNA virus likely belonging to the family Totiviridae. The objective of this study was to evaluate the genetic variation in Norwegian PMCV isolates focusing on the putative structural proteins encoded by open reading frames (ORFs) 1 and 3. The virus isolates were sampled from a total of 36 farms along the Norwegian coastline. This study represents the first investigation of PMCV genome variation and shows that Norwegian isolates are highly similar, with the most divergent isolates sharing 98.6% nucleotide identity. Interestingly, amino acid sequence diversity within ORF3 is approximately threefold higher than for ORF1. While phylogenetic analysis based on concatenated nucleotide data covering ORF1 and ORF3 revealed four main clusters, the maximum sequence variation of 1.4% at the nucleotide level suggests that all Norwegian isolates belong to a single genogroup. Substantial sequence variation within farms was also observed, which may complicate future molecular epidemiological investigations. The genetic homogeneity among the Norwegian isolates might facilitate development of both diagnostic tools and an efficient vaccine against CMS in the future.