Combining a weed traits database with a population dynamics model predicts shifts in weed communities

A functional approach to predicting shifts in weed floras in response to management or environmental change requires the combination of data on weed traits with analytical frameworks that capture the filtering effect of selection pressures on traits. A weed traits database (WTDB) was designed, populated and analysed, initially using data for 19 common European weeds, to begin to consolidate trait data in a single repository. The initial choice of traits was driven by the requirements of empirical models of weed population dynamics to identify correlations between traits and model parameters. These relationships were used to build a generic model, operating at the level of functional traits, to simulate the impact of increasing herbicide and fertiliser use on virtual weeds along gradients of seed weight and maximum height. The model generated ‘fitness contours’ (defined as population growth rates) within this trait space in different scenarios, onto which two sets of weed species, defined as common or declining in the UK, were mapped. The effect of increasing inputs on the weed flora was successfully simulated; 77% of common species were predicted to have stable or increasing populations under high fertiliser and herbicide use, in contrast with only 29% of the species that have declined. Future development of the WTDB will aim to increase the number of species covered, incorporate a wider range of traits and analyse intraspecific variability under contrasting management and environments

A TaqMan real-time PCR assay for Rhizoctonia cerealis and its use in wheat and soil

Rhizoctonia cerealis causes sharp eyespot in cereals and the pathogen survives as mycelia or sclerotia in soil. Real-time Polymerase Chain Reaction (qPCR) assays based on TaqMan chemistry are highly suitable for use on DNA extracted from soil. We report here the first qPCR assay for R. cerealis using TaqMan primers and a probe based on a unique Sequence Characterised Amplified Region (SCAR). The assay is highly specific and did not amplify DNA from a range of other binucleate Rhizoctonia species or isolates of anastomosis groups of Rhizoctonia solani. The high sensitivity of the assay was demonstrated in soils using a bulk DNA extraction method where 200 μg sclerotia in 50 g of soil were detected. DNA of the pathogen could also be amplified from asymptomatic wheat plants. Using the assay on soil samples from fields under different crop rotations, R. cerealis was most frequently detected in soils where wheat was grown or soil under pasture. It was detected least frequently in fields where potatoes were grown. This study demonstrates that assays derived from SCAR sequences can produce specific and sensitive qPCR assays

An ecological future for weed science to sustain crop production and the environment. A review

Sustainable strategies for managing weeds are critical to meeting agriculture's potential to feed the world's population while conserving the ecosystems and biodiversity on which we depend. The dominant paradigm of weed management in developed countries is currently founded on the two principal tools of herbicides and tillage to remove weeds. However, evidence of negative environmental impacts from both tools is growing, and herbicide resistance is increasingly prevalent. These challenges emerge from a lack of attention to how weeds interact with and are regulated by the agroecosystem as a whole. Novel technological tools proposed for weed control, such as new herbicides, gene editing, and seed destructors, do not address these systemic challenges and thus are unlikely to provide truly sustainable solutions. Combining multiple tools and techniques in an Integrated Weed Management strategy is a step forward, but many integrated strategies still remain overly reliant on too few tools. In contrast, advances in weed ecology are revealing a wealth of options to manage weedsat the agroecosystem levelthat, rather than aiming to eradicate weeds, act to regulate populations to limit their negative impacts while conserving diversity. Here, we review the current state of knowledge in weed ecology and identify how this can be translated into practical weed management. The major points are the following: (1) the diversity and type of crops, management actions and limiting resources can be manipulated to limit weed competitiveness while promoting weed diversity; (2) in contrast to technological tools, ecological approaches to weed management tend to be synergistic with other agroecosystem functions; and (3) there are many existing practices compatible with this approach that could be integrated into current systems, alongside new options to explore. Overall, this review demonstrates that integrating systems-level ecological thinking into agronomic decision-making offers the best route to achieving sustainable weed management

How to use a “virtual field” to evaluate and design integrated weed management strategies at different spatial and temporal scales

International audienc

How much of seed dormancy in weeds can be related to seed traits?

International audienceSeed dormancy contributes to species persistence in unpredictable environments and is a key process to be taken into account in weed dynamics models. As the level of seed dormancy, photosensitivity and the dates of dormancy induction and release are difficult to measure, our objective was to relate weed seed dormancy with morphological, chemical or physiological seed traits and with expert knowledge. Dormancy of four species was studied experimentally during a 2-year seed burial experiment. Experiments were supplemented with data from the literature to increase the number of species analysed, resulting in a data set of 29 species. Proportions of non–dormant seeds were higher for elongated than spherical seeds, even when accounting for phylogenetic relatedness between species. Elongated seeds, which tend to remain on the soil surface in undisturbed habitats, may have been selected for lack of dormancy and immediate germination to limit mortality due to predation. Dormancy increased with seed coat thickness, which can act as a chemical and physical barrier to germination, while no relation was found with seed lipid or protein content. No correlation was found between photosensitivity parameters and any of the species traits analysed. Variations in dormancy dates (induction and release) were highly correlated with average field emergence season estimated from expert knowledge. The observed correlations suggest that the level of dormancy results both from direct and from indirect effects of traits being involved in trade-offs together with seed mortality

Influence des successions culturales sur les maladies du pied et des racines du blé d'hiver

Les conséquences de différentes successions culturales sur les maladies du pied et des racines ont été étudiées sur une culture de blé d'hiver conduite de manière homogène. Les niveaux d'infestation de piétin-verse (Pseudocercosporella herpotrichoides), piétin-échaudage (Gaeumannomyces graminis var tritici) et rhizoctone (Rhizoctonia cerealis) ont été notés à la floraison sur tige et racines. Les résultats obtenus ont permis de proposer un modèle simple de l'effet du précédent et de l'antéprécédent sur les 3 maladies, basé sur le classement des risques des précédents culturaux en 3 groupes : hôte, culture amplificatrice et non-hôte pour le piétin-échaudage et le rhizoctone, hôte fort/faible, culture amplificatrice et non-hôte pour le piétin-verse. Alors que les cultures hôtes tendent à augmenter le risque et les non-hôtes à le diminuer, les cultures du groupe des amplificatrices (maïs, ray-grass...) n'entraînent un risque que si elles sont associées dans le temps à des cultures hôtes.Influence of crop succession on foot and root diseases of wheat. The consequences of different crop successions on foot and root diseases were analysed on a subsequent winter wheat crop managed identically, regardless of crop succession. At flowering, tillers and roots were assessed for eyespot (Pseudocercosporella herpotrichoides), take-all (Gaeumannomyces graminis var tritici) and sharp eyespot (Rhizoctonia cerealis). As a consequence, we can propose a simple model of the effect of the preceding crop and the 1 before that on the 3 diseases. This model is based on a crop classification into 3 groups: host, amplifying crop and non-host for take-all and sharp eyespot; and 'strong/weak' host, amplifying crop and non-host for eyespot. Whereas host crops tend to increase and non-host crops to decrease disease risk, amplifying crops (maize, ryegrass, etc) can only increase risk if they are associated with host crops