Are similar landscapes the result of similar histories?

This landscape study was based on the sampling of 20 replicated landscape sites (1 km² each) that were located within the floodplain of the river Seine. For each site, 13 landscape variables were measured at three dates (1963–1985–2000). The aim of this study was to investigate the overall landscape variability through its different dimensions (space vs. time) and to assess the relative importance of each dimension. We used a new statistical method, i.e., partial triadic analysis (PTA), which allowed us to assess both (1) the spatial variability of the floodplain landscape and its dynamics in time and (2) the dynamic trajectories of the landscape variables for each site. The results showed, at the floodplain scale, the same landscape pattern has emerged since 1963, although a major trend was observed which consisted in a decrease in meadows resulting from an increase in arable crops. At the site scale, landscape sites, even if they were all influenced by this general trend during the 40-year period, showed contrasting trajectories. These results suggest that similar sites in 2000 do not necessarily share common histories and that contrasting sites in 2000 may have originated from similar patterns in 1963. The issue of biodiversity surrogates is then discussed, suggesting that new landscape metrics should be developed, emphasising spatial variability and (or) temporal dynamics.     

French isolates of Phytophthora infestans from potato and tomato differ in phenotype and genotype

Prior to 1996, the A2 mating type of Phytophthora infestans was not detected on potato in France, but was found at one site on tomato in 1995. This finding lead to the question of the extent of differences and relationships existing between the populations of P. infestans present on each host. A collection of 76 isolates collected in France, mainly in 1996, from potato and tomato was characterised for mating type, allozyme genotype at the Gpi and Pep loci, and mitochondrial DNA haplotype; 74 of these isolates were also characterised for multilocus RFLP fingerprint, and 62 for virulence. All isolates except four showed allozyme genotypes (Gpi 90/100 or 100/100, Pep 83/100 or 100/100) and mtDNA haplotypes (Ia or IIa) characteristic of the populations introduced into Europe in the late 1970s. The four exceptions were isolates collected from tomato in Southern France in 1988-1991, which showed some characteristics of the former European populations (Gpi 86/100, Pep 92/100, mtDNA Ib). Both mating types were present among the collections from both hosts, but isolates with the A2 mating type were found on potato only in one garden crop, adjacent to tomato. Nine different RG57 fingerprints were observed, with a greater diversity among tomato isolates. Furthermore, tomato and potato collections differed markedly in the frequencies of genotypes present. Finally, tomato isolates generally had a lower virulence complexity than potato isolates. These data suggest that P. infestans populations on tomato and potato are largely separated, despite the occurrence of limited gene flow.     

Characterisation of Erwinia carotovora subspecies and detection of Erwinia carotovora subsp. atroseptica in potato plants, soil and water extracts with PCR-based methods

A PCR-RFLP test based on a pectate-lyase encoding gene permits the detection of several Erwinia carotovora subspecies, but requires complete DNA extraction. This paper reports on the suitability of a simplified PCR-RFLP protocol to characterise E. carotovora strains and on the performance of PCR, using the same primers, to detect the atroseptica subspecies in substrates of epidemiological significance. A collection of 140 strains from various hosts and geographical origins was characterised for biochemical traits and PCR-RFLPs. PCR performed on boiled bacterial suspensions yielded an amplification product of 434 bp in 109 of the 140 strains. None of the E. carotovora subsp. betavasculorum strains was amplified, even after complete DNA extraction. RFLPs of the PCR product yielded 24 groups, 3 of which were new. Twenty one groups were specific to one subspecies. Several strains biochemically similar to E. carotovora subsp. atroseptica, but growing at 37 °C, showed PCR-RFLP profiles characteristic of E. carotovora subsp. carotovora. Phenetic and cladistic analyses gave three main domains, not strictly related to hosts or geographical origins. The atroseptica (RFLP groups 1 and 2) and wasabiae (group 21) subspecies constituted one of the domains, despite clustering distantly from one another. Host specialisation and molecular homogeneity suggest a clonal structure within these subspecies. Conversely, E. carotovora subsp. odorifera, despite its limited host range and geographical distribution, and E. carotovora subsp. carotovora showed great molecular diversity, spreading respectively across five and 19 RFLP groups. These two subspecies shared RFLP groups 4, 5 and 6. The tree nodes in the phenograms showed a low robustness when bootstrapping the data matrix. PCR coupled with a 48h enrichment step in a polypectate-rich medium improved detection thresholds of E. carotovora subsp. atroseptica (1.5.10²- 1.5.10³ bacteria/ml in leaves, stems, and tuber peel extracts to 4.10⁷ bacteria/ml in wash water) relative to either immunomagnetic separation coupled with PCR or DAS-ELISA (2.10⁵ in plant samples to 2.10⁷ bacteria/ml in wash water).     

Review on the epidemiology and dynamics of BSE epidemics

The paper describes how the comprehensive surveillance of bovine spongiform encephalopathy (BSE) and studies carried out on these data has enhanced our knowledge of the epidemiology of BSE. Around 7, 000 BSE cases were detected through the screening of about 50 million cattle with rapid tests in Europe. It confirmed that the clinical surveillance had a poor capacity to detect cases, and also showed the discrepancy of this passive surveillance efficiency between regions and production types (dairy/beef). Other risk factors for BSE were being in a dairy herd (three times more than beef), having a young age at first calving (for dairy cattle), being autumn-born (dairy and beef), and being in a herd with a very high milk yield. These findings focus the risk on the feeding regimen of calves/heifers. Several epidemiological studies across countries suggest that the feedborne source related to meat and bone meal (MBM) is the only substantiated route of infection - even after the feed ban -, while it is not possible to exclude maternal transmission or milk replacers as a source of some infections. In most European countries, the average age of the cases is increasing over time and the prevalence decreasing, which reflects the effectiveness of control measures. Consistent results on the trend of the epidemic were obtained using back-calculation modelling, the R(0) approach and Age-Period-Cohort models. Furthermore, active surveillance also resulted in the finding of atypical cases. These are distinct from previously found BSE and classified in two different forms based on biochemical characteristics; their prevalence is very low (36 cases up to 1st September 2007), affected animals were old and some of them displayed clinical signs. The origin and possibility of natural transmission is unknown.     

Improving models of forest nutrient export with equations that predict the nutrient concentration of tree compartments

? The objective of this study was to explore the distribution of major nutrients (N, P, K, Ca and Mg) in the aboveground compartments of an intensively managed tree species (Pinus pinaster Ait.). A total of 53 trees were cut down in even-aged stands respectively 8, 16, 26, 32 and 40 years old. The nutrient concentrations of the aboveground compartments were analysed.

? Nutrient concentrations of foliage did not vary with any of the variables used, except needle age. Nutrient concentrations of living branches, stem bark, stem sapwood, stem heartwood, stemwood and stem decreased with increasing branch diameter, bark thickness, sapwood thickness and heartwood thickness, respectively. Beyond a certain value of the predictive variable (stem diameter ≈ 15 cm; branch diameter ≈ 2.5 cm), the concentration of all the nutrients stabilised.

? A 50 year-old pine stand was used to obtain a validation dataset for nitrogen concentration. For this nutrient, the regression relationships gave satisfactory estimates for most compartments (mean error = 12–25%) and particularly for the stem.

? A procedure is proposed to estimate the nutrient exports associated with harvests of Pinus pinaster biomass.

     

Effects of minimal temperatures on low-linolenic rapeseed oil fatty-acid composition

Rapeseed oil is rich in alpha-linolenic acid (C18:3) and has a low content in saturated fatty acids. It is therefore considered as a very healthy edible oil. However, its high polyunsaturated fatty acid content makes it sensitive to temperature oxidation and therefore not suitable for deep-frying. Low-linolenic varieties with C18:3 content lower than 3.5% have been bred, but a large variability of alpha-linolenic acid content has been often observed in agricultural production of these new lines. Identifying factors affecting the fatty acid profile of oilseed rape should make it possible to produce rapeseed with alpha-linolenic acid content lower than 2.5% and therefore more suitable for frying and other uses in the food industry.Fatty acid composition is affected by environmental conditions, temperature being the main factor. Previous works showed that for conventional double-low rapeseed varieties, low minimal temperatures during the 60 days following the onset of flowering were related to higher alpha-linolenic acid contents.Monitoring the fatty acid profile in low-linolenic varieties from the beginning of seed filling to full maturity showed that alpha-linolenic acid synthesis occurred mainly between 550 and 850 degree-days (base 0 °C) after the onset of flowering, that is during the 20 first days of seed filling in Swiss conditions, i.e. 41–60 days after the onset of flowering. During this period, the determination coefficient of a second order regression between final alpha-linolenic acid (C18:3) content and minimal daily temperature was even better, with R² = 0.87. A significant positive relation was also found for the regression between minimal temperature and oleic acid (C18:1) content for the cultivar Splendor (R² = 0.77) but no correlation could evidence a relation between temperature and linoleic acid (C18:2) content.An easier way to show the relationship between linolenic acid content and minimal temperatures is based on the assumption that fatty acid desaturases regulated by temperature are active at low temperatures only. It consists in counting how many times during this period daily minimal temperature reaches a minimal threshold temperature of 13 °C. The relationship between final alpha-linolenic acid content and the number of days with minimal temperature below 13 °C is as good as the one presented before, i.e. with a determination coefficient, R² = 0.85. This simple model could be used to determine the growing areas with low linolenic acid content.     

DNA methylation and histone acetylation: genotypic variations in hybrid poplars, impact of water deficit and relationships with productivity

? Several reports on annual plants have already shown the involvement of epigenetic modifiers such as DNA methylation in their adaptation to abiotic stresses.

? Nevertheless, the genotypic variations of epigenetic modifiers, their possible correlations with morphological traits and the impact of water deficit have not been described for perennial plants.

? Six genotypes of Populus deltoides × P. nigra were subjected or not to a moderate water deficit treatment. Various morphological traits such as the height of the plants, their biomass and the total leaf area were measured to characterize the productivity in both conditions. Levels of DNA methylation, histone acetylation and the activities and isoform accumulation of the corresponding enzymes were measured at the shoot apex, the site of morphogenesis. Genotypic variation was observed for the morphological traits and the epigenetic variables and correlations were established among them. Genotypic variation for DNA methylation was detected in hybrid poplars. A positive correlation was demonstrated between DNA methylation percentage and productivity under well watered conditions.

? While there was a general decrease of growth for all genotypes in response to a moderate water deficit, genotypic dependant variations of DNA methylation were found suggesting different strategies among hybrids.

     

An equine joint friction test model using a cartilage-on-cartilage arrangement

This study describes an equine joint friction test using a cartilage-on-cartilage arrangement and investigates the influence of age and load on the frictional response. Osteochondral plugs were extracted from equine shoulder joints (2–5 years, n = 12; 10–14 years, n = 15), and mounted in a pin-on-disc tribometer. The frictional response was then measured under constant conditions (2 N; 20 °C; 5 mm/s), and with increasing load (2 N, 5 N, 10 N). In all experiments, the friction coefficient of young cartilage was significantly (P < 0.001) smaller than obtained from old cartilage, while the application of a greater load resulted in a significant (P < 0.001) decrease in friction coefficient only in old cartilage. It was concluded that cartilage ageing was responsible for an increase in friction coefficient under these experimental conditions. Moreover, where young cartilage lubrication remained stable, cartilage ageing may have been responsible for lubrication regime change. The cartilage-on-cartilage model could be used to better understand lubrication regime disturbances in healthy and diseased equine joints, and to test the efficacy of various bio-lubricant treatments.     

Rehabilitation practices that shape cocoa agroforestry systems in Central Cameroon: key management strategies for long-term exploitation

In Africa’s main cocoa producing countries, rehabilitation of old cocoa orchards is increasingly debated but rarely adopted. In Central Cameroon, rehabilitation practices are regularly set up in old cocoa-based agroforestry systems (cAFS). To better understand the impact of such practices we built a chronosequence of 40 cAFS. We carried out specific surveys with farmers on each plot in order to check for rehabilitation effects on cocoa stands and associated woody species (AWS). We found that cocoa trees represented on average 88.2% of woody individuals and increased with age (from 84.7 to 91.5%). The cocoa stand basal area (BA) share significantly increased with age and reached up to 40.2% in the oldest systems. Cocoa, fruit and forest trees mean BA increased with aging. They were on average of 6.5, 5.7 and 10.7 m² ha^?1 respectively. Six different architectural types, different from the theoretical architectural evolution of cocoa trees over time, were identified. Among them, type 4 characterized by several orthotropic suckers of differing ages, was found typical of farmers’ cutting back practices. Type 4 cocoa trees density increased over time and its BA represented on average 60% of cocoa stand BA in the oldest systems. Concomitantly, farmer’s management of AWS led to continuous evolution of the systems both in terms of density and species composition. Our results show that (i) permanent densification and cutting back practices (type 4) allow the rejuvenation of cocoa stands while increasing cocoa stands BA share; (ii) the continuous management of AWS by farmers is undertaken to favour cocoa trees share over time by limiting inter-specific competition and promoting complementarity between cocoa trees and AWS. We argue that such practices explain a fair part of the long-term sustainability observed in cAFS from Central Cameroon and represent a model from which new rehabilitation schemes could be inspired.