Denitrification in a cultivated soil: Optimal glucose and nitrate concentrations

An experiment was conducted in the laboratory on a cultivated soil incubated in serum bottles with a range of C-to-nitrate concentrations. C was added in form of glucose and nitrate in form of Ca(NO₃)₂. It was shown that an C-N concentration of respectively 500 μg C (glucose-equivalent, Glc-Eq.) and 36 μg N g⁻ dry soil was optimal for denitrification. Results obtained either in the laboratory, in soil columns or in the field were in good agreement with one another. In particular, the root zone was shown to be favorable for denitrifying activity because the water-soluble C (Glc-Eq.) and N concentrations were more favorable than in bare soil. Furthermore, the water-soluble extractable Glc-Eq. appeared to be closely related to the denitrification rate and is thus likely to represent the energetic C pool supporting denitrification.

This was related to an inhibiting effect of increasing NO₃⁻ and NO₂⁻ concentrations on NO₃⁻ loss and N₂O production. Such inhibition can affect short-term measurements of denitrification in the field.     

In vitro pre-exposure of Haemonchus contortus L3 to blood eosinophils reduces their establishment potential in sheep

Different authors have reported that eosinophils are capable of immobilising infective larvae of different species of nematodes in vitro. However, classifying larvae as mobile or immobile is so subjective that it does not always mean all apparently immobile larvae are dead or those that are mobile are capable of surviving further immune responses if administered to their natural hosts. The objective of this experimental study was therefore to substantiate the role of eosinophils in the killing of Haemonchus contortus infective larvae by comparing the infectivity in sheep of larvae that had been incubated with eosinophil-enriched cell suspensions with control larvae. Since it was not possible to isolate pure eosinophils from sheep blood, we were compelled to evaluate the effects of other blood cells contaminating our eosinophil-enriched suspensions. Although eosinophils and neutrophils were the only cells found adherent to H. contortus infective larvae in vitro, induced eosinophils in the presence of immune serum were primarily responsible for the drastic reduction in larval motility compared to the minor effects of neutrophils and mononuclear cells. Corresponding reductions in faecal egg count and worm numbers were observed when the incubated larvae were transferred intra-abomasally to sheep. Interestingly, the proportion of larvae that failed to establish was much higher following incubation with induced eosinophils compared with other cells or with immune serum alone. Although this study did not address the in vivo role of eosinophils in sheep, the results strongly indicate that sheep blood eosinophils have a larval killing potential in vitro, and a larval mobility test alone may not fully explain the level of damage inflicted on the larvae.     

DNA sequence polymorphisms and their application to bread wheat quality

Single-nucleotide polymorphisms (SNPs) constitute an abundant source of DNA polymorphisms, which have been successfully used to identify loci that are associated with a particular phenotype. Additionally, such markers could be efficiently used in combination with doubled haploid technology to improve the efficiency of breeding programmes. Information on such markers in plants is still scarce. For bread wheat, SNP data are restricted to a few genes. This can be explained by the hexaploidy of Triticum aestivum which makes SNP discovery difficult. We developed a novel method for SNP discovery in bread wheat. The strategy is based on the development of highly specific PCR-primers, which were used to sequence 27 lines. SNPs were discovered from sequence alignment data. Some SNPs were identified by mass spectrometry in a collection of 113 lines, which were both evaluated for agronomic traits and genotyped at 42 neutral microsatellite loci. Traits investigated include: protein content, the quantity of high-molecular-weight glutenins and that of the GluBx subunit. The 42 markers were used to infer population structure, which was included in linear models for association studies. The results of this preliminary study showed 89 SNPs in approximately 20 kbp, i.e., one SNP every 223 bp on average. Six SNPs were genotyped: three were located along the sequence of Glu-B1-1, while three non-synonymous SNPs were located along the sequence of the B homoeologous gene coding for SPA (Storage Protein Activator). The SNPs from Glu-B1-1 had a significant effect on the studied variables, whereas those of SPA had no effect. Such results might indicate that some haplotypes for Glu-B1-1 are linked to higher protein content, through an increased amount of high-molecular-weight glutenins, especially the GluBx subunit.     

Effect of Dietary Essential Fatty Acids and Vitamins on Egg Quality in Turbot Broodstocks

Varying egg quality is one of the main factors interfering with the reliable performance of marine fish hatcheries. As larval performance during the first period largely depends on the availability of essential nutrients, the endogenous provision of these nutrients through the egg stages, and possibly parental diet, might be an important tool in improving hatchery output. Therefore, several feeding experiments were conducted on turbot (Scophthalmus maximus) broodstock reared under production conditions at two commercial facilities in France: France Turbot (FT) and Sepia Conseil (SC). Diets varied mainly in essential fatty acids (-3 HUFA), Vitamins C and E, and were fed for 2–3 months prior to the reproductive season. Egg quality parameters, i.e. fertilization and hatching rate, egg and oil droplet diameter, and biochemical composition, were monitored for each female during its total reproductive phase.Egg size during the reproductive cycle showed a low variability among females receiving the same treatment, but became significantly smaller as the season progressed. The same occurred for the oil globule in the non-vitamin supplemented groups, whereas it significantly increased in the vitamin-supplemented groups. However, these observations could not be correlated with any of the hatching or fertilization characteristics. The egg dimensions also varied as a function of the diet supplied, i.e. high HUFA levels in the broodstock diet resulted in a significant increase of egg diameter, oil globule diameter as well as fertilization rate. Interestingly, the control groups, with the lowest fertilization rate, had the highest hatching percentage, significantly higher than the HUFA/non-vitamin enriched groups.Using non-selected sources of trash fish as a food source at SC resulted in low levels of ascorbic acid (AA) in the eggs compared to the administration of an optimal quality batch of mackerel at FT. Enrichment of the trash fish with ascorbate-2–polyphosphate (ApP) resulted in a tripling of the AA content. Extra enrichment of the FT control diet did not further increase the levels in the eggs, suggesting that a saturation level was obtained. The major fatty acids in turbot eggs as well as freshly hatched larva are 16:0, 18:1-9, 20:5-3 and 22:6-3, but no obvious changes in their pattern could be detected for the different broodstock treatments. However, the level of 20:4-6 was significantly higher in the control group of FT, and showed a high correlation with the hatching percentage of the eggs obtained from the various broodstock treatments.     

CAPRA: the EPPO Computer Assisted PRA scheme*

The EPPO Secretariat has developed computer software for Pest Risk Analysis (PRA) within the EC 7th Framework Programme PRATIQUE (Enhancements of Pest Risk Analysis Techniques) and with the support of the EPPO Panels. The software, Computer Assisted PRA (CAPRA), aims to assist pest risk analysts to run the EPPO Decision‐support scheme for pest risk analysis [EPPO Standard PM 5/3(5) Decision‐support scheme for quarantine pests], and other decision‐support schemes. It is freely avaliable on the EPPO website or on http://capra.eppo.org/ .