Validation d’un tableau de bord d’indicateurs sur un réseau national de fermes en grande culture et en viticulture pour diagnostiquer la qualité biologique des sols agricoles

Ce numéro comprend les articles correspondant aux présentations du Colloque Casdar 2017.National audienceWithin a context of agroecological transition, the Agrinnov project validated a set of indicators of the biological quality of agricultural soils to enable farmers to grasp the impact of their practices. AgrInnov project brought researchers and farmers to work together. To accompany the set of indicators of soil fauna, microbiology and agronomy, training sessions on soil biology have also been implemented together with an appropriate transfer procedure. The training sessions and the set of indicators were spread on a national network of more than 250 field-crop and viticulture farms. From an operational viewpoint, more than 97% of the farmers invested heavily in the project and stayed involved throughout Cannavacciulo M. et al. 42 Innovations Agronomiques 55 (2017), 41-54 the project. From a scientific viewpoint, less than 10% of the tested plots were assessed to be in a critical state in terms of soil biology, which is encouraging on agricultural soil quality, even though the monitoring should be developed on a broader number of farms and production systems in order to have a more exhaustive and representative diagnosis. Thus the AgrInnov project demonstrated the application and adoption by the farmers of new research-based tools for diagnosing soil quality.Dans un contexte de transition agroécologique, le projet Agrinnov a permis de valider un tableau de bord d’indicateurs analytiques de la qualité biologique des sols agricoles permettant aux agriculteurs d’appréhender l’impact de leurs pratiques. Le projet AgrInnov a amené des chercheurs et des agriculteurs à collaborer. En parallèle du tableau de bord (comprenant des indicateurs de faune du sol, de microbiologie et agronomiques), des formations sur la biologie des sols ont été élaborées ainsi qu’un mode opératoire de transfert. Les formations et le tableau de bord ont été déployés sur un réseau national de plus de 250 fermes en grande culture et en viticulture. D’un point de vue scientifique, il a été démontré que moins de 10% des parcelles testées étaient dans un état critique en termes de biologie du sol ce qui est encourageant sur la qualité des sols agricoles, même si il faudrait développer leur surveillance sur un plus grand nombre de fermes et de systèmes de production afin d’avoir un diagnostic plus exhaustif et représentatif. D’un point de vue opérationnel, plus de 97% des agriculteurs ont suivi le projet jusqu’au bout avec un fort investissement de leur part. Par conséquent, le projet AgrInnov a fait la démonstration opérationnelle de l’application et de l’appropriation par les agriculteurs des nouveaux outils de diagnostic de la qualité des sols émanant directement de la recherche

Rhizosphere bacterial communities associated with disease suppressiveness stages of take-all decline in wheat monoculture

International audience• The decline of take-all disease (Gaeumannomyces graminis var. tritici), which may take place during wheat monocropping, involves plant-protecting, rootcolonizing microorganisms. So far, however, most work has focused on antagonistic fluorescent pseudomonads. Our objective was to assess the changes in rhizobacterial community composition during take-all decline of field-grown wheat. • The study was based on the development and utilization of a taxonomic 16S rRNA-based microarray of 575 probes, coupled with cloning–sequencing and quantitative PCR. Plots from one experimental field grown with wheat for 1 yr (low level of disease), 5 yr (high level of disease) or 10 yr (low level of disease, suppressiveness reached) were used. • Microarray data discriminated between the three stages. The outbreak stage (5 yr) was mainly characterized by the prevalence of Proteobacteria, notably Pseudomonas (Gammaproteobacteria), Nitrosospira (Betaproteobacteria), Rhizobacteriaceae, Sphingomonadaceae, Phyllobacteriaceae (Alphaproteobacteria), as well as Bacteroidetes and Verrucomicrobia. By contrast, suppressiveness (10 yr) correlated with the prevalence of a broader range of taxa, which belonged mainly to Acidobacteria, Planctomycetes, Nitrospira, Chloroflexi, Alphaproteobacteria (notably Azospirillum) and Firmicutes (notably Thermoanaerobacter). • In conclusion, take-all decline correlated with multiple changes in rhizobacterial community composition, far beyond the sole case of pseudomonads

Enhanced biodegradation of hexachlorocyclohexane (HCH) in contaminated soils via inoculation with Sphingobium indicum B90A.

Soil pollution with hexachlorocyclohexane (HCH) has caused serious environmental problems. Here we describe the targeted degradation of all HCH isomers by applying the aerobic bacterium Sphingobium indicum B90A. In particular, we examined possibilities for large-scale cultivation of strain B90A, tested immobilization, storage and inoculation procedures, and determined the survival and HCH-degradation activity of inoculated cells in soil. Optimal growth of strain B90A was achieved in glucose-containing mineral medium and up to 65% culturability could be maintained after 60 days storage at 30 degrees C by mixing cells with sterile dry corncob powder. B90A biomass produced in water supplemented with sugarcane molasses and immobilized on corncob powder retained 15-20% culturability after 30 days storage at 30 degrees C, whereas full culturability was maintained when cells were stored frozen at -20 degrees C. On the contrary, cells stored on corncob degraded gamma-HCH faster than those that had been stored frozen, with between 15 and 85% of gamma-HCH disappearance in microcosms within 20 h at 30 degrees C. Soil microcosm tests at 25 degrees C confirmed complete mineralization of [(14)C]-gamma-HCH by corncob-immobilized strain B90A. Experiments conducted in small pits and at an HCH-contaminated agricultural site resulted in between 85 and 95% HCH degradation by strain B90A applied via corncob, depending on the type of HCH isomer and even at residual HCH concentrations. Up to 20% of the inoculated B90A cells survived under field conditions after 8 days and could be traced among other soil microorganisms by a combination of natural antibiotic resistance properties, unique pigmentation and PCR amplification of the linA genes. Neither the addition of corncob nor of corncob immobilized B90A did measurably change the microbial community structure as determined by T-RFLP analysis. Overall, these results indicate that on-site aerobic bioremediation of HCH exploiting the biodegradation activity of S. indicum B90A cells stored on corncob powder is a promising technology