Evolution of grapevine downy mildew (Plasmopara viticola) aggressiveness in response to host partial resistance

International audienceThe increasing use of plants resistant to fungal pathogens in agro-ecosystems may lead to the evolution of plant pathogen populations. Pathogen adaptation to partially resistant host varieties would imply the evolution of life history traits linked to aggressiveness (quantitative pathogenicity). Understanding how pathogen quantitative traits respond to the introduction of host partial resistance is a crucial step toward an accurate management of disease resistance to ensure its sustainability over time. Here, we estimated aggressiveness in grapevine downy mildew (Plasmopara viticola) in a cross-inoculation experiment using a broad range of quantitative traits [e.g. disease severity, sporangia production, sporangia size, latent period, rate of zoospore liberation]. Plasmopara viticola isolates were collected on 9 susceptible varieties (N = 55 isolates) and 14 resistant varieties (N = 55 isolates) and inoculated on the susceptible V. vinifera cv. Cabernet Sauvignon and on partially resistant genotypes (Regent, Prior and Bronner). Specifically, we addressed the following questions: Are pathogen isolates collected on resistant and susceptible varieties able to infect partially resistant genotypes? Do they exhibit similar levels of aggressiveness and which traits are involved? Do isolates from resistant and susceptible varieties exhibit similar aggressiveness on a susceptible variety? Is there any trade-off between aggressiveness components? The main results include: (i) most of the P. viticola isolates collected on different resistant varieties were able to infect both Regent and Prior varieties and exhibited significant higher sporulation than isolates from susceptible varieties; (ii) isolates from resistant and susceptible varieties exhibited similar level of aggressiveness in terms of sporulation when inoculated on the susceptible Cabernet Sauvignon variety; (iii) increase in sporangia number was correlated with a reduction in sporangia size illustrating how partial plant disease resistance can impact selection of pathogen's life-history traits. These results highlight that P. viticola aggressive isolates from various resistant varieties exhibit a high level of sporulation on partially resistant grapevine genotypes. Overall, there was no significant cost of virulence. Plant pathogen populations may rapidly evolve to adapt to partially resistant grapevine varieties and the quantity of sporangia produced and sporangia size were the key traits involved in the adaptation process

Spatial–Spectral Analysis of Hyperspectral Images Reveals Early Detection of Downy Mildew on Grapevine Leaves

Downy mildew is a highly destructive disease of grapevine. Currently, monitoring for its symptoms is time-consuming and requires specialist staff. Therefore, an automated non-destructive method to detect the pathogen before the visible symptoms appear would be beneficial for early targeted treatments. The aim of this study was to detect the disease early in a controlled environment, and to monitor the disease severity evolution in time and space. We used a hyperspectral image database following the development from 0 to 9 days post inoculation (dpi) of three strains of Plasmopara viticola inoculated on grapevine leaves and developed an automatic detection tool based on a Support Vector Machine (SVM) classifier. The SVM obtained promising validation average accuracy scores of 0.96, a test accuracy score of 0.99, and it did not output false positives on the control leaves and detected downy mildew at 2 dpi, 2 days before the clear onset of visual symptoms at 4 dpi. Moreover, the disease area detected over time was higher than that when visually assessed, providing a better evaluation of disease severity. To our knowledge, this is the first study using hyperspectral imaging to automatically detect and show the spatial distribution of downy mildew on grapevine leaves early over time

OSCAR, a national observatory to support the deployment of new grapevine disease resistant varieties in France

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Leaf microbiome data for European cultivated grapevine (Vitis vinifera L.) during downy mildew (Plasmopara viticola) epidemics in three wine-producing regions in France

International audienceGrapevine downy mildew (Plasmopara viticola) is a major disease of European cultivatedgrapevine (Vitis vinifera L.) against which a large amount of synthetic pesticides are used. Developing microbial biocontrol of P. viticola could reduce the use of pesticides in viticulture and preserve human and environmental health. To achieve this goal, the ecological interactions that develop during infection between P. viticola and the vine foliar microbiome need to be explored. Here, we present metabarcoding datasets describing the bacterial and fungal communities of pairs of symptomatic and asymptomatic leaf samples collected during downy mildew epidemics in three major wine-producing regions of France. Fungal and bacterial communities were sequenced on a MiSeq Illumina platform, and the abundance of the oomycete P. viticola was quantified using qPCR. We provide the raw metabarcoding datasets, the amplicon sequence variant tables obtained after bioinformatic processing, the metadatadescribing sampling sites and tissue health conditions, and the code used for bioinformatic analysis. These datasets will enable microbiome comparison within pairs of symptomatic and asymptomatic samples collected at the same time on the same leaf. Such a comparison could help describe the ecological interactions between P. viticola and the grapevine foliar microbiome

Cépages résistants : la vigne contre-attaque

National audienc