Le dugong [Dugong dugon (Müller, 1776) sirenia,dugongidae] en république de djibouti

In 1979 and 1980 strandings, accidental captures and observations of animals at sea established the regular occurrence of the dugong in inshore waters of the Republic of Djibouti. Aerial surveys conducted at the end of 1980 located a small group of some 30 individuals, the largest herd ever recorded in the Red Sea and the Gulf of Aden.     

<Emphasis Type="Italic">Verticillium</Emphasis> disease of <Emphasis Type="Italic">Agaricus bisporus</Emphasis>: variations in host contribution to total fungal DNA in relation to symptom heterogeneity

The pathogenic fungus Verticillium fungicola, responsible for dry bubble disease of the common mushroom Agaricus bisporus, causes various symptoms on its host, bubbles (undifferentiated spherical masses), bent and/or split stipes (blowout) and spotty caps. Host DNA quantification by real-time PCR was used to observed relationships between the type of symptom and the relative amount of A. bisporus and V. fungicola in diseased mushrooms. Verticillium fungicola is involved in bubble formation but does not appear to regulate its growth. Quantifications in bubbles and stipe-bubbles (morphology between bubble and sporophore with stipe blowout) showed that the pathogen has no effect on the growth of undifferentiated host hyphae but prevents morphological differentiation if not initiated and stops it when initiated hyphae are affected. Mushrooms with stipe blowout exhibiting both mature and abortive lamellae reveal that V. fungicola has a restricted area of action in host tissues. Despite their visual aspect, healthy looking parts of mushrooms showing spots or stipe blowout were actually contaminated. Discolouration and symptom development are two distinct events. The colour of the tissues was correlated to the percentage of A. bisporus DNA, suggesting that discolouration is not an efficient defensive mechanism, and occurs at the time V. fungicola developed enough to induce tissues necrosis.     

Regeneration strategies in a temperate hardwood floodplain forest of the Upper Rhine: sexual versus vegetative reproduction of woody species

The regeneration mechanisms of woody species in the hardwood floodplain forest of the Upper Rhine are not well known, although they are of primary importance for future forest development. To gain a better understanding of the balance between sexual and asexual regeneration strategies and to assess the role of the seed bank in regeneration, the similarities in species composition and abundance of four fundamental compartments involved in regeneration (the seed rain, the seed bank, the recruits and the canopy) were compared in three hardwood forest stands with different flooding conditions. The results show that the floristic composition of the recruits is very similar to that of the canopy, whereas the composition of the seed bank is very dissimilar to the latter and comprises very few hardwood species. However, some species such as Fraxinus excelsior, Carpinus betulus and Acer pseudoplatanus which are very rare in the seed bank release a high number of diaspores, and seedlings of these species germinate abundantly in the field in the year following seed release. Moreover, the germinating seeds originate from the litter layer and not from the soil itself. This shows that most woody species regenerating by seed in the hardwood Rhine forest build transient seed banks and that the role of persistent seed banks for regeneration is very limited. Furthermore, it appears that many woody species have developed strategies favouring vegetative propagation for their regeneration, particularly understorey species, such as Cornus sanguinea and Prunus padus. As vegetatively grown individuals better withstand prolonged inundation in their early life stages than seedlings, species relying on vegetative regeneration strategies might be advantaged by regular and prolonged flooding of the Rhine forest over species regenerating only by seeds.     

A digital photographic method for 3D reconstruction of standing tree shape

A digital photographic method is presented which is able to reconstruct the profile of the stem on standing trees up to a height of 12 m and to provide a fine level of detail. The method uses two digital photographs taken at 90° to each other and does not require special illumination conditions. A method is proposed to perform the data acquisition process from the two photographs and to transform the stem dimensions and 3-D position from pixels to units of length. The accuracy of this method for measuring tree shape was tested by comparing the results with those obtained from a laser system. The comparison showed that the photographic method provides a good assessment of standing tree shape.     

Teaching veterinary radiography by e-learning versus structured tutorial: a randomized, single-blinded controlled trial

Case-based e-learning may allow effective teaching of veterinary radiology in the field of equine orthopedics. The objective of this study was to investigate the effectiveness of a new case-based e-learning tool, compared with a standard structured tutorial, in altering students' knowledge and skills about interpretation of radiographs of the digit in the horse. It was also designed to assess students' attitudes toward the two educational interventions. A randomized, single-blinded, controlled trial of 96 fourth-year undergraduate veterinary students, involving an educational intervention of either structured tutorial or case-based e-learning, was performed. A multiple-choice examination based on six learning outcomes was carried out in each group after the session, followed by an evaluation of students' attitudes toward their session on a seven-point scale. Text blanks were available to students to allow them to comment on the educational interventions and on their learning outcomes. Students also rated, on a Likert scale from 1 to 7, their performance for each specific learning outcome and their general ability to use a systematic approach in interpreting radiographs. Data were analyzed using the Mann-Whitney test, the t-test, and the equivalence test. There was no significant difference in student achievement on course tests. The results of the survey suggest positive student attitudes toward the e-learning tool and illustrate the difference between objective ratings and subjective assessments by students in testing a new educational intervention.     

Variations in leaf mass per area according to N nutrition, plant age, and leaf position reflect ontogenetic plasticity in winter oilseed rape (Brassica napus L.)

Leaf mass per area (LMA) is a parameter the variability of which contributes to architectural plasticity. However its variations according to environment remain not completely understood. We hypothesise that LMA variations of winter oilseed rape (WOSR) follow an ontogenetic trajectory that can be modified by the environment. This was assessed at plant and leaf levels comparing four genotypes field-grown under different environmental conditions characterised by year and nitrogen nutrition. Leaves of the main stem of plants sampled between emergence and harvest were surfaced, oven-dried and weighed to calculate LMA of each individual leaf. At the plant level, LMA presented a common ontogenetic trajectory, which increases from seedling emergence to bolting and from then on decreases. Variations in LMA were related to the variations in plant demand, LMA decreased when demand increased. The trajectory was modified by low N nutrition that increased LMA but differently according to year and genotype, reflecting the plant plasticity. At the leaf level, variations for each individual leaf were related to the variations at the plant level. Plant plasticity and genotypic variability of the responses of LMA to N deficiency seemed to be related to differences in biomass allocation between leaves and stems.     

Correction of moisture effects on near infrared calibration for the analysis of phenol content in eucalyptus wood extracts

? Methods based on near infrared spectroscopy used to assess wood properties are susceptible to variations in physical parameters (temperature, grain size, etc.). As wood is a hygroscopically sensitive material, we studied the effects of moisture on near infrared absorbance and calibration to accurately determine the application potential of this technique under routine.

? A collection of Eucalyptus urophylla × E. grandis hybrid wood pieces were analysed to obtain reference calibration of polyphenol contents in wood extracts via NIR spectra acquired under constant moisture conditions. Other specimens from the same source were assessed to obtain spectra for eight moisture contents spanning a broad variation range. The effects of moisture on absorption and on estimates based on a reference model were analysed.

? An increase in moisture content prompted a rise in near infrared absorption over the entire spectrum and for water O-H absorption bands. The polyphenol content estimates obtained by assessing specimens against the reference calibration at variable moisture contents revealed prediction bias. Five correction methods were then tested to enhance the robustness relative to moisture.

? In-depth calibration and external parameter orthogonalization (EPO) were found to be the most efficient methods for offsetting this factor.

     

Management zone delineation using a modified watershed algorithm

Site-specific management (SSM) is a common way to manage within-field variability. This concept divides fields into site-specific management zones (SSMZ) according to one or several soil or crop characteristics. This paper proposes an original methodology for SSMZ delineation which is able to manage different kinds of crop and/or soil images using a powerful segmentation tool: the watershed algorithm. This image analysis algorithm was adapted to the specific constraints of precision agriculture. The algorithm was tested on high-resolution bio-physical images of a set of fields in France.