Innovations et actualités en agriculture : bio contrôle, micro-organismes, moyens de lutte alternative, intrants, pratiques culturales, OAD, agronomie...
La sélection de l'actualité agricole par Lallemand Plant Care
Pour diminuer les effets de la compaction au semis, Colin Hurd de l’État de l’Iowa, a ajouté des roues avec des dents travaillant le sol juste derrière le châssis principal du planteur.
L’utilisation de planteurs de plus en plus large avec de plus en plus de trémies centrales pour les semences et les engrais ajoute du poids et accentue les problèmes de compaction au moment où la terre est la plus sensible.
Didier Barral, vigneron bio à Lentheric (Hérault) a opté pour un système de polyculture-élevage. Il a délimité ses vignes de haies pour lutter contre l'érosion des sols, protéger la biodiversité et la zone de captage d'eau.
Editorial: Almost all land plant species form a symbiosis with mycorrhizal fungi. These soil fungi provide nutrients and other services to plants in return for plant carbohydrates. The recent application of microbial metagenomics, metatranscriptomics, and metabolomics to plants and their immediate surroundings confirms the key role of mycorrhizal fungi, rhizosphere bacteria and fungi, and suggests a world of hitherto undiscovered interactions (van der Heijden et al., this issue, pp. 1406–1423). This novel knowledge is leading to a paradigm-shifting view: plants cannot be considered as isolated individuals any more, but as metaorganisms, or holobionts (Hacquard & Schadt, this issue, pp. 1424–1430) encompassing an active microbial community re-programming host physiology (see Pozo et al., this issue, pp. 1431–1436). This bears tremendous implications for plant ecophysiology and evolution, plant breeding, crop management and sustainable ecosystem management.
Mycorrhizal associations are centerpieces in this wide cortege of plant-associated soil biota. To exploit these evolving insights, critical gaps need to be filled in our current understanding of mycorrhizal interactions. This special issue of New Phytologist addresses fundamental gaps and contains 30 new contributions on mycorrhizal science, covering topics from genomes to ecosystems. These contributions result from the 33rd New Phytologist Symposium Networks of power and influence: ecology and evolution of symbioses between plants and mycorrhizal fungi (Zürich, 14–16 May 2014, http://www.newphytologist.org/symposiums/view/4; see also Bender et al., 2014).
A series of key questions addressed in this issue explore some of the most cutting-edge approaches, and include: (1) How is the balance of mutualism maintained between plants and fungi? (2) What is the role of mycorrhizal fungi in the soil ecosystem? (3) What controls fungal community composition, and how is diversity maintained? While many of these questions originated in the earliest days of mycorrhizal science (Koide & Mosse, 2004), the development of new tools and approaches, from genomics to mathematical models to isotopes, is allowing them to be addressed in greater detail, clarity and depth than ever before.
En perte de vitesse depuis plus de 30 ans, l'agriculture française connaît ces derniers mois une période particulièrement difficile avec des revenus catastrophiques dans presque toutes les filières. Radiographie et bilan.
Medicago truncatula belongs to the legume family and forms symbiotic associations with nitrogen fixing bacteria, the rhizobia. During these interactions, the plants develop root nodules in which bacteria invade the plant cells and fix nitrogen for the benefit of the plant. Despite massive infection, legume nodules do not develop visible defence reactions, suggesting a special immune status of these organs. Some factors influencing rhizobium maintenance within the plant cells have been previously identified, such as the M. truncatula NCR peptides whose toxic effects are reduced by the bacterial protein BacA. In addition, DNF2, SymCRK, and RSD are M. truncatula genes required to avoid rhizobial death within the symbiotic cells. DNF2 and SymCRK are essential to prevent defence-like reactions in nodules after bacteria internalization into the symbiotic cells. Herein, we used a combination of genetics, histology and molecular biology approaches to investigate the relationship between the factors preventing bacterial death in the nodule cells. We show that the RSD gene is also required to repress plant defences in nodules. Upon inoculation with the bacA mutant, defence responses are observed only in the dnf2 mutant and not in the symCRK and rsd mutants. In addition, our data suggest that lack of nitrogen fixation by the bacterial partner triggers bacterial death in nodule cells after bacteroid differentiation. Together our data indicate that, after internalization, at least four independent mechanisms prevent bacterial death in the plant cell. These mechanisms involve successively: DNF2, BacA, SymCRK/RSD and bacterial ability to fix nitrogen.
Paysan Breton Les couverts multi-espèces recyclent plus d'azote Paysan Breton Cette gestion des couverts est surtout possible pour les adeptes du semis direct, dont fait partie Frédéric Thomas, dans un couvert déprimé au glyphosate ou broyé, en...
When I attended the meeting on ‘Molecular Microbe–Plant Interaction’ in Rhodes (6–10 July 2014) this summer, I had the feeling that a relevant change was taking place. The meeting is traditionally devoted to investigations of plant–microbe communication and gives the most attention to the molecular relationships between plants and pathogenic or symbiotic microbes, to signal transduction and to the characterization of virulence factors in bacteria and fungi. This year, however, the 2014 Rhodes meeting opened its doors to a plenary lecture entitled ‘The Phyllosphere Microbiome’ presented by Julia Vorholt (ETH Zurich) and to sessions like ‘The Plant Microbiome’ and ‘Evolution and Ecology’, which were well received by large audiences. Just a couple of examples from these sessions: starting from their previous characterization of the microbiota associated with Arabidopsis (Bulgarelliet al., 2012), Paul Schulze-Lefert demonstrated how Arabidopsis thaliana shares a largely conserved microbiota with its relatives, revealing quantitative species-specific footprints (Schlaeppi et al., 2014). Moving from characterization to function, the Schulze-Lefert group has started a systematic analysis of root microbiota functions under laboratory conditions. Interestingly, the first step required the isolation of 70% of the members of the A. thaliana root-enriched microbiota as pure cultures and the further generation of annotated whole-genome sequence drafts for all the cultivated rhizobacteria. Moving above ground, Vorholt pointed out in her lecture that leaves represent one of the largest terrestrial habitats for microorganisms. Also, in this case, after the identification of the main bacterial groups, the researchers aimed to understand the general strategies by which bacteria adapt to the phyllosphere, a very special habitat involving exposure to drastic, always-fluctuating conditions. Most of the presentations related to the microbiota field led to similar conclusions: as observed for the human microbiota, the bacterial root microbiota appears to have a major role in promoting plant growth and providing indirect protection against pathogens. Interestingly, to verify such hypotheses, traditional, cultivation-dependent approaches have to be examined, in addition to data from the much more recent cultivation-independent analyses.
What does this mean? I reasoned that the use of similar omics approaches in environmental microbiology and in molecular biology-based researches has led to the merger (or at least to a closer approach of) these fields, which only some years ago were very far apart. Questions like ‘which host genetic factors shape microbial populations in a given environment’ and ‘how does a plant interact with a plethora of microbes, activating or not activating its immune system’, may have more convergent responses when expertise from molecular ecology, genomics transcriptomics and metabolomics converges. It seems that the concept of systems biology has also incorporated knowledge of microbial ecology.
In this environmental-genomics context, the emerging field of fungal–bacterial interactions is assuming a new dimension. On the one hand, studies of the plant microbiota have mostly focused on bacteria, with only a few recent papers demonstrating that fungi play equally important and widespread roles (Orgiazzi et al., 2013; Smith and Peay, 2014). The obvious next step with such new data is to understand whether these two crucial microbial components interact, and, if the reply is positive, how they interact. Indeed, the novel question of fungal–bacterial relationships is not exclusive to the plant microbiota: Frey-Klett and colleagues (2011) produced a very accurate summary demonstrating that bacterial–fungal interactions are fundamental to agriculture, clinical and natural environments, as well as in food technology. Their novel results also demonstrated how fungi and bacteria coexist in the human body. What is our microbiome doing and how does it interact with bacteria? In their Nature paper, Findley and colleagues (2013) elegantly demonstrated that physiological attributes and topography of human skin differentially shape the pathogenic and commensal communities of fungi and bacteria. They conclude that the interaction between these microbes is crucial to the maintenance of human health and to disease pathogenesis. A Jacques Monod conference (http://www.cnrs.fr/insb/cjm/2013/Frey-Klett_e.html) devoted to the topic revealed an unexpectedly broad and interdisciplinary audience: soil microbiologists like Wietse de Boer and Dirk Van Elsans in The Netherlands alternated with speakers from hospitals and medical schools (Deborah Hogan and Gordon Ramage, United Kingdom) as well as speakers from food and wine departments, shedding new light on the relevance of interactions between prokaryotes and eukaryotes.
Of course, the crucial open questions involve the mechanisms behind these inter-domain interactions, as well as whether specificity exists and the identities of the involved molecular determinants. Results from the A. Brackage and C. Hertwech laboratories in Jena offer strong evidence on the communication between soil bacteria and fungi. The plant-pathogenic fungus Rhizopus microsporus hosts a bacterium, Burkholderia rizoxini, which is involved in the production of the pathogenicity factor rhizoxin, exclusive of the interaction (Partida-Martinez and Hertweck, 2005). The intimate contact between a soil Streptomyces and the human-pathogenic Aspergillus fumigatus leads to the activation of novel metabolic pathways, regulated by activator genes as well as by epigenetic factors (Nützmann et al., 2011; König et al., 2013). Such discoveries suggest that close fungal–bacterial encounters may have unpredictable consequences for diverse aspects of fundamental and applied biology.
Understanding fungal–bacterial interactions may also offer clues to new fields: for example, we are used to thinking that symbiosis is the result of two organisms that live together. However, an increasing body of knowledge demonstrates that bacterial communities often form crucial components of a symbiosis. Lichens offer a good example of this claim: algae and fungi strictly interact with many diverse bacterial communities, which probably also exert physiological functions (Grube et al., 2014). Systems biology approaches will be instrumental in dissecting the specific roles of all the partners. Similarly, mycorrhizas can be described as tripartite interactions where bacteria colonize the hyphal surface and act as helper bacteria (Frey-Klett et al., 2007), or may live inside the cytoplasm of arbscular mycorrhizal fungi (Bonfante and Anca, 2009; Bonfante, 2014). The discovery that a very ancient and still enigmatic group of endobacteria described as Mollicutes-related endobacteria (Mres) occurs inside the spores of most Arbuscular Mycorrhizal (AM) fungi (Naumann et al.,2010; Desirò et al., 2014) opened the door for many studies on the biodiversity of these endobacteria, which probably represent the top of a still-hidden iceberg. The discovery that Mres are present not only inside AM fungi but also inside the hyphae of other basal fungi, like the Mucoromycotina Endogone, opens new scenarios on the evolution of plant-associated fungi and bacteria (Desirò et al., 2015).
In conclusion, a combination of omics approaches, advanced phylogenetic studies and genetics experiments, all inserted in an evolutionary biology framework, will allow us, on the one hand, to extend our knowledge on bacterial–fungal biodiversity, and, on the other, to better understand the mechanisms underlying these interactions. Mixing environmental approaches and functional-genetics studies will be instrumental to providing a deeper understanding. Environmental Microbiology is already on this track.
1.From the phytocentric perspective, a mycorrhizal network (MN) is formed when the roots of two or more plants are colonized by the same fungal genet. MNs can be modelled as interaction networks with plants as nodes and fungal genets as links. The potential effects of MNs on facilitation or competition between plants are increasingly recognized, but their network topologies remain largely unknown. This information is needed to understand the ecological significance of MN functional traits.
2.The objectives of this study were to describe the interaction network topologies of MNs formed between two ectomycorrhizal fungal species, Rhizopogon vesiculosus and R. vinicolor, and interior Douglas-fir trees at the forest stand scale, identify factors leading to this structure and to contrast MN structures between forest plots with xeric versus mesic soil moisture regimes.
3.Tuberculate mycorrhizas were sampled in six 10 x 10 m plots with either xeric or mesic soil moisture regimes. Microsatellite DNA markers were used to identify tree and fungal genotypes isolated from mycorrhizas and for comparison with reference tree boles above-ground.
4.In all six plots, trees and fungal genets were highly interconnected. Size asymmetries between different tree cohorts led to non-random MN topologies, while differences in size and connectivity between Rhizopogon species-specific sub-network components contributed towards MN nestedness. Large mature trees acted as network hubs with a significantly higher node degree compared to smaller trees. MNs representing trees linked by R. vinicolor genets were mostly nested within larger, more highly connected R. vesiculosus-linked MNs.
5.Attributes of network nodes showed that hub trees were more important to MN topology on xeric than mesic sites, but the emergent structures of MNs were similar in the two soil moisture regimes.
6.Synthesis: This study suggests MNs formed between interior Douglas-fir trees and R. vesiculosus and R. vinicolor genets are resilient to the random loss of participants, and to soil water stress, but may be susceptible to the loss of large trees or fungal genets. Our results regarding the topology of MNs contribute to the understanding of forest stand dynamics and the resilience of forests to stress or disturbance.
Un consortium de recherche public-privé va être lancé afin de « développer une industrie française du biocontrôle », c'est-à-dire des méthodes de protection des cultures alternatives aux produits phytos, sous la houlette de l'Institut national de la recherche agronomique (Inra).
L’objectif général du projet PEPITES est de produire des connaissances sur les processus écologiques, les processus d’innovation technique et sociale, et leurs interactions, pour évaluer et concevoir des systèmes techniques et des dispositifs d’accompagnement plus durables.7
Les travaux se déroulent sur quatre terrains d’étude (France grandes cultures, France agriculture biologique, Brésil et Madagascar petite agriculture familiale) choisis pour explorer une gamme de situations agropédoclimatiques et socioéconomiques permettant une analyse comparative riche.
Réduire son IFT hors herbicides de 21 à 5,8 en trois ans, et ses charges d’intrants phytosanitaires de 950 à 213 €/ha, c'est le pari fou qu'a réussi Jean-Bernard Mussotte. Ce viticulteur girondin, basé à Mazères, voulait avant tout réduire ses charges et ne plus dépendre des prescriptions des fournisseurs de produits phytosanitaires.
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