La santé des plantes passe par la santé des sols

National audienc

Ecological role of mycotoxin and consequences of the presence of mycotoxins in crop residues on the survival and pathogenic activity of Fusarium graminearum

National audienc

Impact of deoxynivalenol on soil microflora and fauna

National audienceF. graminearum is an important pathogen that causes head blight of cereal crops as wheat and maize. It also produces the mycotoxins (as Deoxynivalenol=DON) which are toxic to the human and animals. During the off season the pathogen survives in the soil, on weeds and in crop residues. A 24 weeks study was conducted in controlled conditions (microcosms of natural soil, 17 °C, 80% WHC) to test whether the presence of DON in the wheat crop residues gives competitive advantage to F. graminearum over the other soil microflora and fauna to survive and develop a primary inoculum during the decomposition process. This study was carried out in the presence of the whole soil biota (i.e. fungi, bacteria, protozoa, nematodes and earthworms). In this experimental approach, wheat straw was inoculated with F. graminearum. The latter was placed on the soil surface or incorporated into the natural soil. This experiment was conducted with (1mg DON/kg soil-straw mixture) and without DON. The molecular biomass of fungi, bacteria and F. graminearum was determined by qPCR (real time polymerase chain reaction). The changes in the community structure of fungi, bacteria, protozoa and nematodes were determined by T-RFLP (terminal restriction fragment length polymorphism). The results suggested that DON in wheat straw showed an impact on part of the biotic components of the soil but the impact depended on the communities and on the location of the wheat residues

Saprophytic survival of Fusarium graminearum in crop residues

National audienceFusarium Head Blight (FHB) is one of the most important disease altering wheat crops. A field experiment was conducted to better understand the saprotrophic development of Fusarium graminearum and its consequences on FHB, to characterize the relative importance of the different sources of FHB inoculum and the accumulation of mycotoxins in grains and subsequently, to determine early indicators of future disease development on ears and accumulation of mycotoxins in grains. The development of F. graminearum in the soil and crop residues was monitored in controlled conditions. The inoculum hosted by seeds and/or buried with crop residues in the topsoil had only an effect on the winter development of the disease. In contrast, the main source of inoculum causing FHB disease on ears and accumulation of mycotoxins in wheat kernels came from residues left on the soil surface. Monitoring of plant development from sowing to harvest, crop management and soil and weather conditions produced a large database. Unfortunately, the role of climate was decisive in the development of the Fusarium-host plant interaction, thus prevented the use of early indicators to accurately predict the risks of yield losses and accumulation of mycotoxins involved. F. graminearum was regulated by the soil microflora. However, crop residues provide the fungus spatial and trophic niches favourable to its development. The exploitation of these niches by F. graminearum depends on the nature (previous crop and C/N) of the residues. Maize stubbles provide a greater carrying capacity than wheat straw and rapeseed residues while mustard has a suppressive effect for the fungus. The management of crop residues is a key point to control the development of FHB. A strong emphasis should be placed on the biological decomposition of crop residues at the soil surface or/and on the use of suppressive intermediate crops such as mustard to limit the soil inoculum potential of saprotrophic F. graminearum

Jack et les légumineuses magiques face au réchauffement climatique. Atelier grand public

National audienceAvec le réchauffement climatique, les plantes sont soumises à différents stress, dont le stress hydrique et les fortes températures. Ces stress ont des conséquences négatives importantes sur les cultures et sur les éléments indispensables à la croissance et au développement des plantes, notamment l’azote et le fer.Dans cet atelier, nous allons vous montrer les pistes sur lesquelles les chercheurs se penchent pour comprendre comment les plantes peuvent résister à ces changements

Ecological role of mycotoxins in wheat crop residues and consequences on the multitrophic interactions in the soil and further development of Fusarium graminearum

Affiche, résuméFusarium graminearum causes wheat head blight disease and produce differentmycotoxins (as Deoxynivalenol=DON) which are toxic for human and animal. During off season itsurvives in the soil, on weeds and in crop residues. A 6 months study was conducted in controlledconditions (microcosms of natural soil, 17°C, 80%WHC) to test whether the presence of DON inthe wheat crop residues gives advantages to F. graminearum to survive and develop a primaryinoculum during the decomposition process. This study was carried out in the presence of the wholesoil biota (i.e. fungi, bacteria, protozoa, nematodes and earthworms). Both F. graminearum and thebiota were monitored during the decomposition process. The wheat crop residues were placed onthe soil surface or incorporated into the natural soil. This experiment was conducted with (1mgDON/kg soil-straw mixture) and without DON. This study suggested that the mycotoxins provideda competitive advantage to F. graminearum and were deleterious towards the fungal communityand the nematodes but not towards the bacteria or the earthworms. However, all the results were notstatistically significant. The use of molecular tools as well as the forthcoming quantification ofDON in the residues during 24 weeks of observation will provide the clarification and may confirmor not the trends we observed

Root rot of pea: characterization and biocontrol of the soil-borne disease complex including Aphanomyces euteiches

National audiencePea root rot is an increasing constraint in most of intensive pea cropping areas across the globe. The pathogenic complex responsible for the disease is composed of soil-borne fungal and oomycete pathogens such as Fusarium solani, F.oxysporum, F. avenaceum, F. culmorum, Rhizoctonia solani, Thielaviopsis basicola, Ascochyta pinodella, Pythium spp., Aphanomyces euteiches and probably others not yet identified. The diversity of their ecological and pathogenic properties can explain the worldwide dispersion of the disease and the absence of chemical, agricultural or genetic control tools. My research program aims at characterizing the parasitic consortium occurring in the North of France and at proposing biocontrol strategies. First, a field sampling strategy is being determined to measure Inoculum Potential and assess A. euteiches risk. In addition, a comparative analysis of the fungal and oomycete diversity from roots and rhizospheres of symptomatic and asymptomatic plants of infested fields is carried out. This analysis consists in a combination of microbiological isolations and molecular methods (Metabarcoding) to characterize the microbial complex responsible for the disease and identify putative biocontrol taxa. Promising candidates and commercial products with a biocontrol activity against oomycetes and fungi which could be part of the microbial complex will be tested in vitro, in greenhouse, and in field

Biocontrol of jimsonweed (datura stramonium l.), a weed toxic to human and animal health

National audienceJimsonweed (Datura stramonium L.) is an invasive weed that produces highly toxic alkaloids, posing a threat to both human and livestock health by infecting crops. The aim of my project is to identify biosolution using fungi (and oomycetes) and/or plant extracts for managing this plant in agricultural fields.195 fungi and oomycetes were isolated from jimsonweed plants showing collar pinching, wilting, yellowing, and root necrosis symptoms. Symptomatic plants were collected either directly from field or from bioassays in growth chambers using soils from crop fields with varying degrees of jimsonweed infestation. The isolates were purified by successive subculturing and cultivated on potato dextrose agar and carnation leaf agar for morphological characterisation. Most of them showed characteristics similar to those of Fusarium spp., Alternaria spp., Rhizoctonia spp. and Pythium spp.. The pathogenicity of different isolates was evaluated through their necrotic activity towards the germ tube and rootlets of germinating jimsonweed seeds, and their ability to cause damping-off on seedlings. Two experiments were conducted. First, pregerminated jimsonweed seeds were placed on pleated germination paper in a Caubère box and hydrated with 50mL of propagule suspension. The rate of necrosis on germ tubes and rootlets was evaluated. The second experiment consisted in transplanting pregerminated jimsonweed seeds into disinfected and non-disinfected substrates (soil/perlite, 70/30, v/v), which were inoculated with propagule suspension to assess the damping-off ability of each isolate. The most efficient isolates were characterised and their specificity evaluated. Two of them, including one that had never been described anywhere and one described only in the US, turned out to be pathogenic to jimsonweed and constitute promising candidates for the control of this weed. The second approach based on the use of substances of plant origin was carried out by spraying a panel of essential oils previously selected via a bibliographic analysis. Eight essential oils (Orange, Eucalyptus, Lavender, Lavandin, Thyme, Savoury, Clove, and Oregano) were sprayed at different concentrations (0.1, 1, 5, 10, 15%) on jimsonweeds at the 2-3 leaf stage. Two essential oils performed very well. A bioguided fractionation of these essential oils is being carried out, in interaction with the Faculty of Pharmacy of Strasbourg (L. Valois) to identify the fractions carrying the bioherbicide activity on jimsonweed and to identify the molecule responsible of the activity.All the results acquired make it possible to meet the objectives of this ICE1 thesis by proposing two products, one of fungal origin, the other of plant origin, which can be used in a complementary manner and constitute a strong component of the biosolutions sought for the jimsonweed control

Biocontrol of weeds toxic to human and animal health

National audienceimson weed (Datura stramonium L.) is an invasive weed plant that produces alkaloids that are particularly toxic to humans (crop contamination) and animals (fodder). The objective of my research project is to find a biocontrol solution based on the use of fungi (even oomycetes) and/or plant extracts to control this plant in agricultural plots. At first, I focus on the research of mycoherbicides. The presence of pathogens or phytotoxic metabolites for jimson weed in a panel of non-infested soils to highly infested soils is tested by applying aqueous extracts or filtrates (0.2µm) of these soil extracts to datura seeds placed on germination paper under controlled temperature and humidity conditions. 80% of the control seeds (supplied with sterile water) germinate on day D+5 while 60% do with the soil extract and 70% with the soil filtrate. This result suggests that microorganisms present in the soil extract, and to a lesser degree phytotoxic molecules present in the filtrate inhibited the development of jimson weed. The fungal diversity of these different soils will be analyzed using high throughput sequencing. This should allow us to look for a link between fungi richness, fungal communities structure, presence of datura and crop management technique. At the same time, one hundred and thirty-one fungal isolates were isolated from jimson weed seedlings exhibiting damping off symptoms, grown in a climatic chamber under controlled temperature and humidity conditions. The pathogenicity of these isolates, among which the most represented genera are Alternaria and Fusarium, is tested using bioassays in climatic chamber. Several stages of datura development will be considered: non-germinated seeds and germinated seeds on germination paper, and seedlings at the two-cotyledon stage in tests in pots containing a compost-perlite mixture to test the pathogenicity of the isolates on the three characteristics of damping off (inhibition of germination, root and crown rotting). I will present you the results of this screening of my 131 isolates during our next doctoral days or during an upcoming internal seminar

Visual assessment and computer–assisted image analysis of Fusarium head blight in the field to predict mycotoxin accumulation in wheat grains

Phenotypic traits are regularly used to diagnose the development of Fusarium head blight (FHB) in the field, whereas mycotoxin accumulation in wheat grains can only be accurately evaluated through costly methods, such as high–performance liquid chromatography (HPLC). The aim of this study was to determine whether: (i) the results providedby existing commercial decision support tools could be anticipated using phenotypic measurements, including a novel technique of computer– assisted image analysis of spikes; and (ii) these measurements could avoid using HPLC. We monitored the FHB development during two consecutive years in highly contaminated plots in the Burgundy region (France). Contamination by crop residues was simulated through a field inoculation with barley grains artificially colonized by Fusarium graminearum. The development of the disease on spikes and harvested grains was assessed on one tolerant and two susceptible wheat varieties. The accumulated amounts of mycotoxins were measured in harvested grains using HPLC. As expected, the measured traits revealed that the inoculum responsible for infection on spikes mainly came from residues left on the soil surface, and the susceptible varieties were more diseased than the tolerant variety.Weather conditions had a strong effect on disease development. The novel computer–assisted image analysis technique had a better prediction power of deoxynivalenol accumulation, was more objective and time–saving than classical visual symptom assessments.This assessment method could be suitable to supplement the use of existing prediction tools and might avoid systematic and costly mycotoxin measurements in likely infected plots