HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
The emergence of new genotypes of parasites involves several evolutionary, epidemiological and ecological processes whose individual effects and interactions are difficult to disentangle using experimental approaches. Here, a model is proposed to investigate how these processes lead to the emergence of plant viral genotypes breaking down qualitative resistance genes. At the individual plant scale, selection, drift and mutation processes shape the evolution of viral populations from a set of differential equations. The spatial segregation of virus genotypes in their hosts is also considered. At the host population scale, the epidemiological dynamics is given by an individual-based algorithm. Global sensitivity analyses allowed ranking the ten demo-genetic and epidemiological parameters of the model according to their impact on the mean and variance of the risk of breakdown of a plant resistance. Demo-genetic parameters (number and nature of mutations involved in breakdown, fitness of mutant genotypes) had the largest impact on the mean breakdown risk, whereas epidemiological parameters had more influence on its standard deviation. It is discussed how these results can be used to choose the potentially most durable resistance genes among a pool of candidates. Finally, our analyses point out the parameters which should be estimated more precisely to improve durability predictions.
A b s t r a c tMaize plants grown in field conditions were used to describe the histological organisation of the nodal roots, those of their laterals, and also to test the presence of critical stages where the subsequent capability for growth and development of young laterals was determined irreversibly. The absence of undeveloped primordia, which stop their development before boring through the nodal mother-root epidermis, proved that the number of laterals could not be regulated between the differentiation and the emission stage. Cross sections performed on nodal roots beared by the internodes 2, 4 and 6 and their long (>3 cm) and short (<3 cm) laterals showed that: -The short laterals have almost the same root and stele diameter, cortex width and xylem size regardless of the insertion position of their mother root. Consequently they stopped their development at nearly the same stage, which seems to be concomitant with late metaxylem vessel differentiation. Thus, 92% of these short roots had only one of these vessels. On the contrary, the dimensions of the tested histological parameters, as well as the numbers of late and early metaxylem vessels and of xylem poles increased with internode rank for both long laterals and nodal roots. Moreover, for the nodal roots issued from internode 6, important decreases (up to 50%) in the sizes of most of the measured parameters were observed along the roots with the distance from the stem insertion point. Complementary experiments performed in mist boxes, under strict homogeneous conditions, showed that the observed variability is not generated by the culture medium. -Up to 750/xm, the root diameter is correlated to most of the histological characters tested. -Nodal roots have a higher proportion of xylem than lateral roots. Consequently their conduction abilities, evaluated using the C/E ratio of Hagen-Poiseuille's law, were particularly important. -No relationship was found between the diameter of a nodal root and those of its laterals.
Abstract. One way in which Apis mellifera honey bees resist Varroa destructor is by detection and elimination of nestmates. This study uses behavioural tests and electroanntennography to assess the role of chemostimuli in recognition by honey bees of this acarian ectoparasite. Behavioural tests using living or dead parasites involved observation of honey bee grooming activity (antennation) under controlled conditions in Petri dishes, and removal behaviour (uncapping and elimination of parasitized and unparasitized control brood cells) under natural conditions. Some bees from colonies with both small and large parasite populations showed aggressive behaviour (biting). No difference was observed according to whether the mite was dead or alive. Under natural conditions, bees uncapped more parasitized cells than control cells. Electroantennographic tests were performed to measure sensitivity to various Varroa extracts at three concentrations (10, 20 and 30 Varroa Equivalents). Only 30 Varroa Equivalent methanol extracts made from Varroa collected from brood cells elicited significantly greater antennal response than controls (pure solvent). All three methanol extracts elicited significantly greater antennal response than controls. No response was observed using Varroa extracts made with acetone or hexane. These findings suggest that polar products may act as chemostimuli for recognition of V. destructor by honey bees. Further study will be necessary to determine which polar products are involved in this recognition and assess grooming and removal behaviour using these products.
Prunus persica = pêcher / qualité / fruit / modèle de croissance / analyse multivariée Summary ― Variability of peach (Prunus Persica L Batsch) growth and quality, and relationships between growth and quality. The individual fruit growth of the peach (Suncrest cultivar), was studied by modelling growth curves based on cheek-diameter measurements. Our model assumed that peach fruit growth; was divided into 2 phases. The first one described the pit growth and the first part of the flesh growth; the second described the second part of the flesh growth (fig 1). The fit of the model was good (fig 2). The growth curves were compared using a particular principal component analysis (PCA) working on the model parameters. The differences between fruits were highest during the second phase (fig 3). The curves were grouped into classes using a cluster analysis running on PCA factors (fig 4). At harvest, quality data, ie pH, soluble solids, sucrose, reducing sugars, citric and malic acids, flesh firmness and skin color, were recorded. Quality variation among fruits was studied using a correspondence analysis and a cluster analysis. The pH did not vary (table I). Acidity, sugars and soluble solids were correlated and described a gustatory gradient (fig 5). Firmness and yellow color were correlated with this gradient. Other color descriptors were correlated to each other and described a coloration gradient which was independent from the gustatory one (fig 6). Four groups of peach fruits were individualized (figs 5, 6). For most quality descriptors, between-class differences were high (table II). The relationship between growth and quality was studied using a canonical correspondence analysis. The peach diameter in April was not correlated with quality (table IV). Growth was more correlated with gustatory quality and firmness than with coloration (tables I and III). Early mature fruits with a high cheek diameter at the end of the first phase had a large amount of purple. The other fruits had a large amount of orange and a high chrominance (fig 9). In fruits with both a significant second growth phase and a high and late maximal growth rate the highest soluble solids and sucrose content and the lowest citric acid content and firmness were found (fig 8). Luminance was not correlated with growth.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.