Réponses moléculaires du pommier et du poirier en interactions compatibles et incompatibles avec Erwinia amylorova, agent du fzu bactérien des maloideae

Erwynia amylorova est l'agent du feu bactérien, maladie du pommier et du poirier. Les déterminants du pouvoir pathogène de cette bactérie sont identifiés (hrp-dsp cluster, capsule, sidérophore) mais les mécanismes moléculaires conduisant à la maladie ou à la résistance ne sont toujours pas connus. Pour tenter de les élucider, nous avons entrepris de comparer les réponses de deux génotypes de pommier (connus pour leurs sensibilités contrastées au feu bactérien) confrontés à E. amylorova, des mutants du pouvoir pathogène de cette bactérie et le 1pathogène incompatible pseudomonas syringae pv. tabaci. Deux stratégies ont été utilisées : 1) l'analyse biochimique et moléculaire de différentes défenses candidates et 2) l'analyse de l'expression différentielle de gènes par cDNA-AFLP. Les résultats mettent en évidence trois sortes dé réponses : 1) des mécanismes sont élicités dans les deux génotypes par E. amylorova et P. s. pv tabaci, selon des cinétiques similaires (choc oxydant, protéines PR)RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

New elicitors to protect winter wheat against Zymoseptoria tritici?

Today, focus is made on the crucial protection of wheat, as one of the most cultivated crop plants in the world. This crop is constantly challenged by a persistent and harmful fungus known as Zymoseptoria tritici, responsible of the Septoria Tritici Blotch (STB) disease. Control of this disease mainly depends on chemical products. However there is an urgentneed to identify and develop alternative methods as biocontrol tools to adopt an efficient IPM program for wheat. Elicitors are increasingly considered as promising biocontrol tools in the preventive treatment of plants against various diseases. These plant-immunity triggering compounds, also called “stimulators of plant natural defenses”, induce a general and systemic resistance of the plant to a large spectrum of biotic stresses. This study focuses on the screening of nine molecules of various origins and structures for their potential eliciting activity, to protect winter wheat against Zymoseptoria tritici. The protective efficacy of these molecules was evaluated under greenhouse conditions by comparing the infection severity of the treated plants with a water control. In addition, the biocide activity of the 9 candidates was tested in vitro directly towards the pathogen, by evaluating their impact on spore germination and fungal growth. Finally, the qPFD tool developed by INRA was used to study the expression of 23 defense genes in the wheat plant following the various treatments. These combined experiments finally allowed the selection of two molecules as potent elicitors: EGL1 and EGL4. They were efficient to reduce foliar disease symptoms from 60 to 80% on wheat under greenhouse conditions. The efficacy of these 2 promising molecules was thus evaluated in 2 field trials in 2016. The corresponding results will be presented and discussed, with the perspective to investigate the efficacy of these 2 potent elicitors to protect wheat cultivars showing different levels of sensitivity towards the pathogen.Développement d'une formulation d'éliciteurs pour lutter contre les bioagresseurs du bl

Feasibility of rating fire blight susceptibility of pear cultivars (Pyrus communis) on in vitro microcuttings

Typical symptoms of fire blight (ooze production and necrosis) can easily be obtained from the inoculation of in vitro microcuttings of a host plant. The purpose of the study was to determine whether the susceptibility of pear cultivars to fire blight can be evaluated in vitro. In a work based on several Pyrus cultivars (susceptible and resistant) propagated in vitro, the effects of different external factors (method of inoculation, concentration of inoculum, growing conditions) on quantitative and qualitative expression of symptoms were analyzed. The variability of the results, already noticed in orchards, was not lessened on this plant material. Inoculations on in vitro microcuttings usually overestimated susceptibility. However, a decrease of the receptivity of susceptible cultivars was sometimes observed. Therefore tests on in vitro microcuttings do not seem to be suitable for accurate discrimination between cultivars based on their different levels of susceptibility. Nevertheless these tests may be useful for selecting out individuals with high levels of resistance from a population (i.e. after mutagenic treatment or induction of somaclonal variations).Si les symptômes typiques du feu bactérien (production d’exsudat et nécrose) sont facilement obtenus sur microboutures in vitro de plantes-hôtes inoculées, est-il possible d’estimer la sensibilité d’un cultivar donné? Travaillant sur différents cultivars de Pyrus (sensible et résistant) multipliés in vitro, l’effet de facteurs externes (méthode d’inoculation, concentration d’inoculum, conditions de culture) sur l’expression quantitative et qualitative de la maladie est analysé. La variabilité des résultats, déjà connue en verger, n’est pas réduite par l’utilisation de ce matériel végétal. Des inoculations sur microboutures donnent souvent une surestimation de la sensibilité mais on observe parfois une diminution de la réceptivité de cultivars sensibles. Ainsi, un test sur microboutures ne paraît pas approprié pour différencier précisément des sensibilités variétales. Cependant, il peut être utilisé pour sélectionner des individus très résistants à l’intérieur d’une population (par exemple après un traitement mutagéne ou l’induction de variations somaclonales)

Nouveaux éliciteurs pour protéger le blé contre la septoriose: des outils de biocontrôle pour la lutte intégrée contre les bioagresseurs

Elicitors are increasingly considered as promising biocontrol tools in the preventive treatment of plants against various diseases. These plant-immunity triggering compounds, also called “stimulators of plant natural defenses”, induce a general and systemic resistance of the plant to a large spectrum of biotic stresses. Today, focus is made on the crucial protection of wheat, as one of the most cultivated crop plants in the world. This crop is constantly challenged by a persistent and harmful fungus known as Zymoseptoria tritici, responsible of the Septoria Tritici Blotch (STB) disease. Control of this disease mainly depends on phytosanitary products, and the social and economic importance of wheat make it all the more urgent to identify and develop new elicitors as biocontrol tools in wheat IPM strategies. This study focuses on the screening of nine molecules of various origins and structures for their potential eliciting properties to protect winter wheat against Zymoseptoria tritici. Three products were selected after screening trials in greenhouse conditions: EGL1, EGL4, and EGL5. They were efficient to reduce foliar disease symptoms from 40 to 80%. The biocide activity and phytotoxicity of these 3 products were evaluated directly towards the pathogen and the plant under laboratory and greenhouse conditions, respectively. On the other hand, the triggered signaling pathways were investigated by studying the activity of the defense-related enzymes lipoxygenase (LOX), peroxidase (POX) and phenylalanine ammonia-lyase (PAL) in treated wheat leaves. In addition, the expression of five defense genes (lox, pal, pox2, chi, pr1) was studied by qRT-PCR in wheat leaves treated with these elicitors and/or inoculated with Zymoseptoria tritici. The corresponding results will be presented and discussed, with the perspective to investigate the influence of environmental parameters on the elicitation capacity and the efficacy of the elicitors in field conditions.Développement d'une formulation d'éliciteurs pour protéger le blé d'hivers contre la septorios

Phytotoxicity and Plant Defence Induction by Cinnamomum cassia Essential Oil Application on Malus domestica Tree: A Molecular Approach

Essential oils (EOs) are actively investigated as an alternative to numerous synthetic biocide products. Due to their large spectra of biological activities, the impact of EOs on non-target organisms should be characterized for biopesticide development purposes. In this study the potential phytotoxicity of Cinnamomum cassia EO (CEO) on apple trees (Malus domestica) was investigated in terms of oxidative burst (glutathione redox state) and damage (malondialdehyde). At 2%, CEO concentration the reduced glutathione leaf content drops from 269.6 ± 45.8 to 143 ± 28.4 nmol g−1 FW, after 30 min, illustrating a rapid and strong oxidative burst. Regarding oxidative damage, malondialdehyde increased significantly 24 h post application to 10.7 ± 3.05 nmol g−1 FW. Plant defence induction was previously suspected after trans-cinnamaldehyde (CEO main compound) application. Therefore, the elicitor potential was investigated by qRT-PCR, on the expression level of 29 genes related to major defence pathways (PR protein, secondary metabolism, oxidative stress, parietal modification). Multivariate analysis and increased expression levels suggest induction of systemic resistance. Hence, the present research illustrates the dose–dependent phytotoxicity of CEO in terms of lipid peroxidation. Transcriptional data illustrates the elicitor properties of CEO. These findings can help to design pest management strategies considering both their risks (phytotoxicity) and benefits (defence activation combined with direct biocide properties)

Attachment, Chemotaxis, and Multiplication of Agrobacterium tumefaciens Biovar 1 and Biovar 3 on Grapevine and Pea

Tumorigenic (CG49) and nontumorigenic (CG484) strains of Agrobacterium tumefaciens bv. 3 attached to grape roots at a higher level than did a nonpectinolytic mutant of CG49 (CG50) or a tumorigenic strain of A. tumefaciens bv. 1 (CG628). Strains attached equally well to wounded and unwounded grape roots. Strains responded differently to pea plants in that biovar 3 strains consistently attached to unwounded roots at a lower level than they did to wounded roots, whereas CG628 attached equally well regardless of wounding. The lowest levels of attachment to pea roots were consistently observed for CG50. Population curves were calculated for the strains inoculated into wound sites on grape and pea roots. A. tumefaciens bv. 3 wild-type strains developed greater populations at wound sites on grape roots after 100 h (resulting in root decay) than did CG50 or CG628. Population curves for strains at wound sites on pea roots were different from those on grape roots. There were no significant differences in populations after 100 h, and no strains caused root decay. No differences in the chemotaxis of wild-type and mutant A. tumefaciens bv. 3 strains towards grape roots, crown pieces, or root extracts were observed, but the biovar 1 strain, CG628, always migrated the greatest distance towards all substrates. Polygalacturonase production may affect attachment to grape roots and multiplication of A. tumefaciens bv. 3 at wound sites and thus be associated with the specificity of the bacterium for grape

Transmission of Plant-Pathogenic Bacteria by Nonhost Seeds without Induction of an Associated Defense Reaction at Emergence▿ †

An understanding of the mechanisms involved in the different steps of bacterial disease epidemiology is essential to develop new control strategies. Seeds are the passive carriers of a diversified microbial cohort likely to affect seedling physiology. Among seed-borne plant-pathogenic bacteria, seed carriage in compatible situations is well evidenced. The aims of our work are to determine the efficiency of pathogen transmission to seeds of a nonhost plant and to evaluate bacterial and plant behaviors at emergence. Bacterial transmission from flowers to seeds and from seeds to seedlings was measured for Xanthomonas campestris pv. campestris in incompatible interactions with bean. Transmissions from seeds to seedlings were compared for X. campestris pv. campestris, for Xanthomonas citri pv. phaseoli var. fuscans in compatible interactions with bean, and for Escherichia coli, a human pathogen, in null interactions with bean. The induction of defense responses was monitored by using reverse transcription and quantitative PCR (RT-qPCR) of genes representing the main signaling pathways and assaying defense-related enzymatic activities. Flower inoculations resulted in a high level of bean seed contamination by X. campestris pv. campestris, which transmitted efficiently to seedlings. Whatever the type of interaction tested, dynamics of bacterial population sizes were similar on seedlings, and no defense responses were induced evidencing bacterial colonization of seedlings without any associated defense response induction. Bacteria associated with the spermosphere multiply in this rich environment, suggesting that the colonization of seedlings relies mostly on commensalism. The transmission of plant-pathogenic bacteria to and by nonhost seeds suggests a probable role of seeds of nonhost plants as an inoculum source

Bestim network : stimulating plant health in agroécological systems

National audienceThe evolution of agriculture is facing strong societal expectations. One of them is to drasticallyreduce the use of synthetic inputs and in particular of plant protection products (PPP). In response,farmers and professionals in charge of agricultural development must invent a so-called "agroecological" agriculture, by ensuring profitability and sustainability of production systems and byimplementing a combination of many levers. The BESTIM network is part of this logic and proposes theconcept of "agroecological immunity" which aims to optimize the stimulation of plant health in efficientagroecological systems. We’ve adapted the concept of ecological immunity initially described in theanimal system (Sadd and Schmid-Hempel, 2009; Schulenburg et al., 2009), to the plant system placed inan agroecological context.Plant health is to be understood here in a broad sense. It covers all the physiological mechanisms thatensure the expression of an efficient immune system that protects the plant from pests and diseaseswhile guaranteeing optimal development (yield, quality) and taking into account its environment(microbiota, abiotic stresses). The objective of the BESTIM network is not limited to understanding thephysiological mechanisms involved in the application of different levers, alone or in combination, thatimpact immunity. It aims, during the 5 years of the approval period (2021 - 2025), to transfer thisknowledge from the laboratory to the field and to associate it with other alternative levers alreadyavailable or being developed to achieve redesigned cropping systems tending towards "low inputs".The RMT BESTIM brings together many organizations wishing to engage collectively in thisagroecological immunity approach: Research institute, universities, Grandes Ecoles, agriculturalHighschool, Technical Institute, R&D centers, Producers associations….You can join the network here: https://rmt-bestim.org

Bestim network : stimulating plant health in agroécological systems

National audienceThe evolution of agriculture is facing strong societal expectations. One of them is to drasticallyreduce the use of synthetic inputs and in particular of plant protection products (PPP). In response,farmers and professionals in charge of agricultural development must invent a so-called "agroecological" agriculture, by ensuring profitability and sustainability of production systems and byimplementing a combination of many levers. The BESTIM network is part of this logic and proposes theconcept of "agroecological immunity" which aims to optimize the stimulation of plant health in efficientagroecological systems. We’ve adapted the concept of ecological immunity initially described in theanimal system (Sadd and Schmid-Hempel, 2009; Schulenburg et al., 2009), to the plant system placed inan agroecological context.Plant health is to be understood here in a broad sense. It covers all the physiological mechanisms thatensure the expression of an efficient immune system that protects the plant from pests and diseaseswhile guaranteeing optimal development (yield, quality) and taking into account its environment(microbiota, abiotic stresses). The objective of the BESTIM network is not limited to understanding thephysiological mechanisms involved in the application of different levers, alone or in combination, thatimpact immunity. It aims, during the 5 years of the approval period (2021 - 2025), to transfer thisknowledge from the laboratory to the field and to associate it with other alternative levers alreadyavailable or being developed to achieve redesigned cropping systems tending towards "low inputs".The RMT BESTIM brings together many organizations wishing to engage collectively in thisagroecological immunity approach: Research institute, universities, Grandes Ecoles, agriculturalHighschool, Technical Institute, R&D centers, Producers associations….You can join the network here: https://rmt-bestim.org

Combined Effects of Long-Living Chemical Species during Microbial Inactivation Using Atmospheric Plasma-Treated Water▿

Electrical discharges in humid air at atmospheric pressure (nonthermal quenched plasma) generate long-lived chemical species in water that are efficient for microbial decontamination. The major role of nitrites was evidenced together with a synergistic effect of nitrates and H2O2 and matching acidification. Other possible active compounds are considered, e.g., peroxynitrous acid