Menace sur la santé des plantes

National audienc

Short-distance dispersal of wheat rust spores

After a brief description of the biophysical environment of diseased plants, mechanisms of short-distance dispersal of wheat rust spores by wind and rain are reviewed. Wind, and especially intermittent gusts, is the main agent of removal and transport of spores. Whereas wind does not seem to limit the process of short-distance dispersal, the effect of rain events is more complex. Laboratory and field experiments have shown that rain events enhance spore removal from sporulating lesions. Rain events also scrub airborne spores and deposit them onto susceptible plants. Extended or violent rain events, however, may finally wash off spores already deposited on leaves and be detrimental to the spread of disease.Dissémination à courte distance des spores des rouilles du blé par le vent et la pluie. Après une brève description de l'environnement biophysique des plantes malades, les mécanismes de dispersion à courte distance des spores des rouilles du blé par le vent et par la pluie sont discutés. Le vent, surtout lorsqu'il est intermittent, est l'agent principal de libération et de transport des spores. Alors que le vent ne semble jamais avoir d'action limitante sur la dispersion des spores à courte distance, l'influence des épisodes pluvieux est plus complexe. Des expérimentations au champ et en laboratoire ont montré que les épisodes pluvieux favorisent la libération des spores à partir des lésions sporulantes. Les épisodes pluvieux lessivent également les spores contenues dans l'air et les déposent sur les plantes sensibles. Cependant, des épisodes pluvieux prolongés ou violents peuvent entraîner le lessivage des spores déjà déposées sur les feuilles, et être ainsi défavorables à la progression de la maladie

Analyse des phases précoces d'une épidémie affectant les organes aériens des plantes : application aux rouilles du blé

Chapitre 14National audienc

Spécifier un processus caché non modélisé en déterminant le lien asymptotique entre résidus et processus caché (application à l'analyse de la variabilité dans les expériences de propagation des rouilles du blé)

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Seasonal Changes Drive Short-Term Selection for Fitness Traits in the Wheat Pathogen Zymoseptoria tritici

International audienceIn a cross-infection experiment, we investigated how seasonal changes can affect adaptation patterns in a Zymoseptoria tritici population. The fitness of isolates sampled on wheat leaves at the beginning and at the end of a field epidemic was assessed under environmental conditions (temperature and host stage) to which the local pathogen population was successively exposed. Isolates of the final population were more aggressive, and showed greater sporulation intensity under winter conditions and a shorter latency period (earlier sporulation) under spring conditions, than isolates of the initial population. These differences, complemented by lower between-genotype variability in the final population, exhibited an adaptation pattern with three striking features: (i) the pathogen responded synchronously to temperature and host stage conditions; (ii) the adaptation concerned two key fitness traits; (iii) adaptation to one trait (greater sporulation intensity) was expressed under winter conditions while, subsequently, adaptation to the other trait (shorter latency period) was expressed under spring conditions. This can be interpreted as the result of short-term selection, driven by abiotic and biotic factors. This case study cannot yet be generalized but suggests that seasonality may play an important role in shaping the variability of fitness traits. These results further raise the question of possible counterselection during the interepidemic period. While we did not find any trade-off between clonal multiplication on leaves during the epidemic period and clonal spore production on debris, we suggest that final populations could be counterselected by an Allee effect, mitigating the potential impact of seasonal selection on long-term dynamics

Les populations de Mycosphaerella graminicola s'adaptent-elles aux modifications saisonnières de leur environnement ?

absen

Influence of host resistance and phenology on South american leaf blight of the rubber tree with special consideration of temporal dynamics

International audienceSouth American leaf blight (SALB), the most dangerous disease of the rubber tree, is responsible for the lack of significant natural rubber production in South America and is a major threat to rubber tree plantations in Asia and Africa. Although the selection of resistant clones is the preferred disease control method, greater knowledge is required of the relationship between host and pathogen, in order to construct more durable resistance. Based on small-scale trials, this study set out to compare the dynamics of SALB on two highly susceptible and one moderately susceptible clone and to analyse the effect of host phenology on disease severity, at leaflet and flush scales. Clonal resistance was found to have a noticeable effect on disease severity, asexual sporulation and stromatal density at both leaflet and flush levels, and on disease dynamics at a leaflet level; time for symptom and sporulation appearance were longer on the moderately susceptible clone than on the susceptible clones. On the moderately susceptible clone, the stromatal density was largely dependent on disease severity. The phenology did not differ among the three clones and could not be considered as a factor in genetic resistance to SALB. However, for the three clones, the position of the leaflet in the flush affected the duration of the immature stages and the disease: the shorter the duration of leaflet development, the lower the disease severity, the sporulation intensity and the stromatal density

Building anisotropic sampling schemes for the estimation of anisotropic dispersal

International audienceAnisotropy, a structural property of dispersal, is observed in dispersal patterns occurring for a wide range of biological systems. While dispersal models more and more often incorporate anisotropy, the sampling schemes required to collect data for validation usually do not account for the anisotropy of dispersal data. Using a parametric model already published to describe the spatial spread of a plant disease, the wheat yellow rust, we carry out a study aimed at recommending an appropriate sampling scheme for anisotropic data. In a first step, we show with a simulation study that prior knowledge of dispersal anisotropy can be used to improve the sampling scheme. One of the main guidelines to be proposed is the orientation of the sampling grid around the main dispersal directions. In a second step, we propose a sequential sampling procedure (SSP) used to automatically build anisotropic sampling schemes adapted to the actual anisotropy of dispersal. The SSP is applied to simulated and real data. The proposed methodology is expected to be adapted easily to any kind of organisms with wind-borne propagule dispersal because it does not require the inclusion of biological features specific of the considered organism