High colonization by native arbuscular mycorrhizal fungi (AMF) of rubber trees in small-holder plantations on low fertility soils in North East Thailand

Rubber tree is a very important crop in Thailand, representing an essential source of income for farmers. In the past two decades, rubber tree plantations have been greatly expanding in unfavorable areas, where climate conditions are difficult and soil fertility is very poor. To optimize latex yields, mineral fertilizers have been widely used. A better understanding of the roles of the biological compartment in soil fertility is essential to determine alternative management practices to sustain soil fertility and optimize latex yields. Arbuscular mycorrhizal fungi (AMF) are widely recognized as beneficial for plants, mainly through their role in improving plant nutrient uptake. The objective of this study was to assess the AMF populations in rubber tree plantations and the impact of both soil characteristics and plantation age on these communities. Our results showed that all rubber trees were highly colonized, regardless of the soil structure and nutrient contents. AMF colonization was not affected by the age of the trees, suggesting that maintaining the symbiosis is likely to be beneficial at all stages. A better understanding and management of the microbial communities would contribute to maintaining or restoring soil fertility, leading to a better tree growth and optimized latex yield.     

Improvement of direct tree seeding with cover crops in afforestation: Microclimate and resource availability induced by vegetation composition

The low cost of direct tree seeding makes it increasingly useful for afforestation. However, the success of the technique is often unpredictable due to a series of different adverse biotic and abiotic factors. A plant cover with low competitive ability towards resources could offer a natural alternative to the herbicides currently used to control weeds. The effects of cover plants on availability of resources and microclimate were studied in a field experiment in the central France during three years. An experiment design crossing three mixtures of tree seeds with four vegetation compositions (a bare soil, flora of the meadow, and two mixtures of cover plants) was established and repeated randomly in three blocks in a meadow. Vegetation composition, tree seedling emergence, light availability, soil water content, and temperatures under each treatment were measured. The vegetation composition of the meadow stayed stable, with grass species dominating. The cover plants sown disappeared rapidly after one or two years. Outcome of direct seeding of trees depended on the vegetation treatment. Bare soil gave the highest emergence rate while meadow vegetation gave the lowest, with the mixture of cover plants being intermediate. Light availability and soil water content were very low under the meadow vegetation but were very high on the bare soil, again with cover plant mixtures being intermediate. This study confirms that a bare soil obtained by herbicide is a secure way to ensure tree seedling establishment in afforestation by direct seeding. However, with the onus currently on reducing herbicide use, the results suggest that sowing a mixture of cover plants could be an acceptable alternative to herbicides. The cover plants could offer protection against frost, scorching temperatures, or the water run-off encountered on bare soil. However, there are also a number of unresolved issues that need be addressed before the cover plants technique can be recommended.     

Impact of topography on cross-pollination in maize (Zea mays L.)

Understanding cross-pollination is important to achieve the coexistence of genetically modified (GM) and conventional maize (Zea mays L.); it is still not known whether topography favors or hinders cross-pollination. In 2005 and 2006, the effect of gradients of 3.4–6.8° on cross-pollination was investigated in the canton of Zurich, Switzerland. Cross-pollination was revealed by the presence of yellow-grains on a white-grain hybrid at distances up to 17.5 m from the yellow-grain pollen donor hybrid. The measurements of the inclination of the slope were based on aerial images data taken by an unmanned GPS/INS (Global Positioning System/Inertial Navigation System)-based and stabilized model helicopter, which delivered precise altitude-based data for sampling points at tassel height.The rate of cross-pollination increased significantly with decreasing altitude of the receptor field (r = 0.36–0.64). However, the effect seems to be weaker than that of other factors like wind direction and velocity.     

“Aberrant” plants in cauliflower: 2. Aneuploidy and global DNA methylation

Aberrant phenotypes of cauliflower were detected throughout the cultivation period and in any variety type. The rate of these phenotypes in the field has recently increased. We reported previously on the first part of our results which showed that (1) the rate of aberrant plants varied with genotype and cultivation area, (2) the aberrant phenotypes can evolve or reverse to normality during the plant cycle and (3) the capacity to express a variant phenotype can be transmitted to the progeny. An epigenetic hypothesis has been proposed to explain the determinism of the phenomenon. Further investigation on the “aberrant” character focussed on the flow cytometric estimation of ploidy levels and on the parallel observation of meiosis. Only a fraction of aberrant plants did show aneuploidy and various ploïdy levels were found for the same phenotype. Indeed, aneuploidy could not be related to the aberrant phenotype although it could probably be a consequence of the aberration phenomenon. HPLC analysis of global DNA methylation rates showed that DNA hypermethylation occurred in plants which exhibited an evolution of their phenotype during vegetative cycle. The epigenetic origin of aberrant phenotypes in cauliflower is discussed with reference to epigenetic diseases described in human beings.     

The present and future of withdrawal period calculations for milk in the European Union: dealing with data below the limit of quantification

The assessment of withdrawal periods for milk is affected by the occurrence of data below the lower analytical quantification limit (BLQ data) and the resulting uncertainty. The current regulatory approach for dealing with BLQ residues is simple and easy: BLQ data (and missing data) are arbitrarily reassigned a value of one‐half the LOQ before any calculation on the data with one of the three currently applicable methods. Here, we reconsider the determination of the withdrawal period of milk with data below the limit of quantification. Theoretical background on analytical limits and pharmacometric considerations will be established. Then, we analyze the uncertainty problems caused by the current approach and propose a calculation solution (maximum‐likelihood estimation handling left‐censored data) included in nonlinear mixed‐effects modeling. Finally, we illustrate this issue using a case example.     

BSAFs for freshwater fish and derivation of a sediment quality guideline for PCBs in the Rhone basin, France

Purpose  

Since 2005, freshwater fish contamination by polychlorobiphenyls (PCBs), polychlorodibenzodioxins, and polychlorodibenzofurans has been assessed in the Rhone River basin (France). A large database of surface sediment contamination by PCBs is also available, opening the way to the study of biota-to-sediment accumulation factor (BSAF) distribution throughout this basin. The ultimate goal of the study was to determine a sediment quality guideline (SQG) corresponding to the regulatory fish consumption limit.     

Seroprevalence of Q fever in naturally infected dairy cattle herds

Coxiella burnetii is the causal agent of Q fever, a worldwide spread zoonosis. Prevention of C. burnetii shedding in cattle is critical to control the spread of the pathogen between animals, and from animals to humans. Vaccination with a phase 1 vaccine has been shown to be effective in preventing shedding when implemented in still susceptible animals, even in infected cattle herds. The identification of these animals (dairy cows and nulliparous females) as targets for vaccination consequently is crucial. Hygiene measures conventionally also are implemented, but their relative impact on C. burnetii diffusion remains unknown. The objectives of this study therefore were to (i) describe the distribution of the within-herd apparent seroprevalence among cows and nulliparous females and (ii) to explore the association between management practices and herd characteristics on the one hand, and these seroprevalences on the other. In a sample of 100 naturally and clinically infected dairy herds, blood samples were taken systematically from all nulliparous females (older than 12 months) and cows, and serologically tested. Information on herd characteristics and management practices were collected through a questionnaire filled in by each farmer. The variation in within-herd seroprevalence among cows and the risk for a herd of having at least one seropositive nulliparous female were investigated using multivariate (linear and logistic respectively) regression models. Median within-herd seroprevalence was 0.32 (Q1=0.22; Q3=0.43). We observed a low to null (median=0.01; Q1=0; Q3=0.10) within-herd seroprevalence in nulliparous females contrary to a high value (median=0.42) and variability (Q1=0.28; Q3=0.56) in cows. Only a few herd characteristics and management practices were found to be related to seroprevalence. Within-herd seroprevalence in cows was found to be significantly (P<0.10) higher in herds (i) with a number of cows<46, (ii) with seasonal calving, and (iii) with grazing or contact through the fence with other ruminant herds. The risk of having at least one seropositive nulliparous female was increased in herds (i) with seasonal calving and (ii) where the foetus and/or the placenta of aborted cows were not systematically removed. Our findings support, in addition to the implementation of high level of hygiene measures, the relevance of vaccination (at least in nulliparous females) as a method to control the spread of C. burnetii within an infected herd, as vaccination is effective in susceptible animals and given that nulliparous females are mostly not infected even in infected herds.     

Plasma lipid lowering effects of wheat germ in hypercholesterolemic subjects

The present study was performed to investigate the possible effects of wheat germ supplementation on lipid metabolism in humans. Ten free-living adult subjects participated in the study. None was obese or diabetic. They all presented an, hypercholesterolemia (from 6.58 to 9.50 mM), associated in 6 over 10 cases to an hypertriglyceridemia (from 1.70 to 5.00 mM). The subjects were studied in three consecutive periods, during which they first were on their usual diet (first week), they then ingested a daily supplement of 30 g wheat germ (4 weeks) and then they returned to their usual basal diet (4 weeks follow-up). Dietary records were obtained for 7 and 3 consecutive days before and during wheat germ supplementation, respectively. Fasting blood samples were taken at the end of each period. After 4 weeks of wheat, germ intake, glycemia did not change while total plasma cholesterol significantly decreased (paired Student'st test,p0.05) from 7.80 to 7.15 mM. LDL and HDL cholesterol values did not show marked changes, but VLDL cholesterol significantly dropped by 40.6%. Thus, the plasma/HDL total cholesterol ratio was significantly lower. Apoprotein B and A1 decreased. In the hypertriglyceridemic subjects, this was accompanied by a significant reduction of plasma triglycerides (1.64 vs. 2.68 mM) and a marked drop of VLDL triglycerides (–51%). Taken as a whole, the present results obtained in humans are very close to those previously obtained in the rat [40] and point out that wheat germ may play a beneficial role in the dietary management of hyperlipidemia.Part of the data communicated in this paper was presented at the Fibre 90 Conference, 17–20 April 1990, Norwich, UK.