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Xylem anatomy may change in response to environmental or biotic stresses. Vascular occlusion, an anatomical modification of mature xylem, contributes to plant resistance and susceptibility to different stresses. In woody organs, xylem occlusions have been examined as part of the senescence process, but their presence and function in leaves remain obscure. In grapevine, many stresses are associated with premature leaf senescence inducing discolorations and scorched tissue in leaves. However, we still do not know whether the leaf senescence process follows the same sequence of physiological events and whether leaf xylem anatomy is affected in similar ways. In this study, we quantified vascular occlusions in midribs from leaves with symptoms of the grapevine disease esca, magnesium deficiency and autumn senescence. We found higher amounts of vascular occlusions in leaves with esca symptoms (in 27% of xylem vessels on average), whereas the leaves with other symptoms (as well as the asymptomatic controls) had far fewer occlusions (in 3% of vessels). Therefore, we assessed the relationship between xylem occlusions and esca leaf symptoms in four different countries (California in the USA, France, Italy and Spain) and eight different cultivars. We monitored the plants over the course of the growing season, confirming that vascular occlusions do not evolve with symptom age. Finally, we investigated the hydraulic integrity of leaf xylem vessels by optical visualization of embolism propagation during dehydration. We found that the occlusions lead to hydraulic dysfunction mainly in the peripheral veins compared with the midribs in esca symptomatic leaves. These results open new perspectives on the role of vascular occlusions during the leaf senescence process, highlighting the uniqueness of esca leaf symptoms and its consequence on leaf physiology.

International audience; In the context of climate change, plant mortality is increasing worldwide in both natural and agroecosystems. However, our understanding of the underlying causes is limited by the complex interactions between abiotic and biotic factors and the technical challenges that limit investigations of these interactions. Here, we studied the interaction between two main drivers of mortality, drought and vascular disease (esca), in one of the world’s most economically valuable fruit crops, grapevine. We found that drought totally inhibited esca leaf symptom expression. We disentangled the plant physiological response to the two stresses by quantifying whole-plant water relations (i.e., water potential and stomatal conductance) and carbon balance (i.e., CO 2 assimilation, chlorophyll, and nonstructural carbohydrates). Our results highlight the distinct physiology behind these two stress responses, indicating that esca (and subsequent stomatal conductance decline) does not result from decreases in water potential and generates different gas exchange and nonstructural carbohydrate seasonal dynamics compared to drought.

Hydraulic failure has been extensively studied during drought-induced plant dieback, but its role in plant-pathogen interactions is under debate. During esca, a grapevine (Vitis vinifera) disease, symptomatic leaves are prone to irreversible hydraulic dysfunctions but little is known about the hydraulic integrity of perennial organs over the short- and long-term. We investigated the effects of esca on stem hydraulic integrity in naturally infected plants within a single season and across season(s). We coupled direct (ks) and indirect (kth) hydraulic conductivity measurements, and tylose and vascular pathogen detection with in vivo X-ray microtomography visualizations. Xylem occlusions (tyloses) and subsequent loss of stem hydraulic conductivity (ks) occurred in all shoots with severe symptoms (apoplexy) and in more than 60% of shoots with moderate symptoms (tiger-stripe), with no tyloses in asymptomatic shoots. In vivo stem observations demonstrated that tyloses occurred only when leaf symptoms appeared, and resulted in more than 50% loss of hydraulic conductance in 40% of symptomatic stems, unrelated to symptom age. The impact of esca on xylem integrity was only seasonal, with no long-term impact of disease history. Our study demonstrated how and to what extent a vascular disease such as esca, affecting xylem integrity, could amplify plant mortality through hydraulic failure.

Hydraulic failure has been extensively studied during drought-induced plant dieback, but its role in plant-pathogen interactions is under debate. During esca, a grapevine (Vitis vinifera) disease, symptomatic leaves are prone to irreversible hydraulic dysfunctions but little is known about the hydraulic integrity of perennial organs over the short- and long-term. We investigated the effects of esca on stem hydraulic integrity in naturally infected plants within a single season and across season(s). We coupled direct (ks) and indirect (kth) hydraulic conductivity measurements, and tylose and vascular pathogen detection with in vivo X-ray microtomography visualizations. We found xylem occlusions (tyloses), and subsequent loss of stemks, in all of the shoots with severe symptoms (apoplexy) and in more than 60% of the shoots with moderate symptoms (tiger-stripe), and no tyloses in shoots that were currently asymptomatic. In vivo stem observations demonstrated that tyloses were observed only when leaf symptoms appeared, and resulted in more than 50% PLC in 40% of symptomatic stems, unrelated to symptom age. The impact of esca on xylem integrity was only seasonal and no long-term impact of disease history was recorded. Our study demonstrated how and to what extent a vascular disease such as esca, affecting xylem integrity, could amplify plant mortality by hydraulic failure.HighlightOur study reveals that esca can critically affect xylem water movement in grapevine perennial organs, by the presence of plant-derived tyloses.

International audience; BACKGROUND: Systemic infection through the seed is one of the routes used by the mycotoxinogenic pathogen Fusarium verticillioides for colonizing maize plants. The prohibition of the use of most chemical fungicides by the EU has promoted research on plant resistance inducers as an effective and sustainable alternative. Induction of a priming state in maize seeds might affect their susceptibility to contamination and accumulation of fumonisins. This state by application of a natural fertilizer called Chamae on maize seeds, was investigated in two varieties to control the colonization by the fungus and the accumulation of fumonisins B 1 , B 2 and B 3 , germinating seeds, dead plants and yield.RESULTS:After inoculation of F. verticillioides on germinating seeds, the colonization by the fungus and the accumulation of fumonisins were significantly lower in seedlings coming from treated seeds, but a significant number of plants stopped their development by necrosis. In a field trial, the 0.01% (v/v) application dilution showed a lower plant density, although the level of biomass at harvest was not affected.CONCLUSION: The priming state contributed to the control of F. verticillioides development from seed infection and fumonisin accumulation in the early stage of plant growth, without affecting the final crop yield, and could reduce fungicide use and environmental contamination. © 2018 Society of Chemical Industry

Fumonisin B1 (FB1 ) is a mycotoxin produced by several Fusarium species and is a very common contaminant of maize-based food and feed throughout the world. The selection and use of FB1 -degrading microorganisms appears as a promising alternative to cope with the problem of toxicity towards humans and livestock. High moisture maize grain silage, which is based on natural maize fermentation, could be an interesting reservoir of such microorganisms.; Results: Using an in vitro simulated silage model with FB1 naturally contaminated grains, we demonstrated a significant raw decrease in FB1 during ensiling process ascribed to biodegradation mechanisms. A panel of 98 bacteria and yeasts were isolated from this matrix and selected for their ability to use FB1 as the sole source of C and N. For nine of them, the ability to degrade FB1 in vitro was evidenced. Notably, two bacteria identified as Lactobacillus sp. were highlighted for their efficient FB1 -degrading capacity and production of hydrolysed FB1 as intermediate degradation metabolite.; Conclusion: Fermentation of high moisture maize grain contaminated with FB1 leads to a significant reduction of the toxin and allows the isolation of FB1 -degrading microorganisms that could further be used as FB1 decontaminating agents. © 2016 Society of Chemical Industry.; © 2016 Society of Chemical Industry.

International audience; The button mushroom Agaricus bisporus is cultivated almost worldwide. Its cultivation is standardized and a temperature of 16-19°C is needed during the fruiting period. The development of A. bisporus cultivars able to fruit at higher temperature (FHT) represents a promising alternative to reduce energy costs during cultivation in hot countries as well as in temperate countries during the hot season. A. bisporus var. burnettii is able to fruit at 25°C. Understanding the biological mechanisms that underlie such a thermo-tolerance is a prerequisite to further development of breeding strains. The foundation of the FHT ability of the var. burnettii was dissected using a combination of candidate gene approaches and genetic tools. Transcript profiling of A. bisporus var. burnettii at two developmental stages (primordium P and sporophore SP) under two fruit-producing temperature conditions (17°C and 25°C) were established by cDNA-AFLP. The expression patterns were more similar within the same stage at the two different temperatures rather than between stages under the same temperature. Only one transcript-derived fragment (TDF) sequence differentially expressed between temperatures was recovered but it could not be further characterized. Twenty-nine TDF sequences differentially expressed between development stages were obtained. The phenotypic assessment of an intervarietal A. bisporus var. bisporus×A. bisporus var. burnettii progeny demonstrated the complex inheritance of the FHT trait. Two quantitative trait loci (QTL) involved in the number of fruit bodies yielded at 25°C were found on LG II and LG VI. Two functional candidate genes known to be potentially involved in A. bisporus thermo-tolerance, a heat shock protein (HSP70) gene and a gene coding for a para-aminobenzoic acid synthase (PABA), were found in the vicinity of the QTL on LG II. Several positional candidate genes have been also identified in the confidence interval of the QTL on LG VI and are promising for further fine mapping purpose.

BACKGROUND The almond mushroom Agaricus subrufescens (formerly Agaricus blazei or Agaricus brasiliensis) is cultivated at commercial level in Brazil and some Asian countries on local substrates and casing mixtures. Despite its tropical origin, A. subrufescens might be a seasonal option for mushroom growers in western countries, where some wild strains have been isolated. For this purpose, cultivation conditions were developed starting from the substrate and casing mixture commonly used for commercial production of the button mushroom Agaricus bisporus in France. RESULTS The commercial compost, based on wheat straw and horse manure, used for A. bisporus and the casing mixture (peat and limestone) supplemented with fine sand proved efficient to grow A. subrufescens. Increasing the depth of the casing layer improved significantly the yield and time to fruiting. Daily variations in temperature did not markedly modify the yield. Significantly higher mushroom biomass was obtained with three wild European strains compared with three Brazilian cultivars. The very productive wild strain CA438-A gave mushrooms of size and dry matter content comparable to those of a cultivar. CONCLUSION Commercial production of A. subrufescens can be developed in western countries on the wheat straw-based substrate commonly used for A. bisporus in these regions, by a simple modification of the casing mixture and maintaining the incubation temperature throughout the crop, which is expected to save energy during summer. Good yields were obtained cultivating European strains under optimised parameters. © 2013 Society of Chemical Industry

Fumonisin BUsing an in vitro simulated silage model with FBFermentation of high moisture maize grain contaminated with FB

Summary In the next few decades, the production of oil fields with high contents of associated sour gases will increase. For instance, it is estimated that 40% of the world's remaining gas reserves contain more than 2% of carbon dioxide (CO2) and/or more than 100 ppm of hydrogen sulphide (H2S). Therefore, investigations on technologies to produce such fields are of utmost importance. Because of the presence of corrosive gas, special attention has to be paid to the design and the selection of materials (steel and cement) used for well construction. Corrosion of steel caused by acid-gas- containing brines is well documented in the literature, and to a lesser extent, data about the degradation by wet CO2 or wet H2S can be found. For cement-based materials, one can find abundant literature dealing with deterioration of cement pastes because of the CO2 environment. Published data on degradation mechanisms of cement-based materials exposed to H2S environments are more scarce. This paper addresses the problem of durability of oilwell cement in different H2S environments. Different periods of time can be identified in the lifetime of the wells—the production period (typically between 20 and 40 years), the post-abandonment period (some tens of years following the permanent well abandonment), and the abandonment period (several centuries). For each period of time, cementing materials (primary cementing, plugs) are in contact with different types of fluids. Therefore, to correctly assess the behavior of oilwell cement, aging tests have to be carried out in fluids representative of these different periods of time. In this paper, we present both the methodology implemented under high-pressure/high-temperature conditions for testing materials in H2S-containing fluids and the results obtained on cement-based materials. Main physicochemical degradation mechanisms of cement-based materials caused by H2S are identified using various characterization techniques. Depending on the nature of the fluid in contact with cement materials, severe degradation can occur with a strong impairment of macroscopic properties.

International audience; Agaricus subrufescens is one of the most important culinary-medicinal cultivable mushrooms with potentially high-added-value products and extended agronomical valorization. The development of A. subrufescens-related technologies is hampered by, among others, the lack of suitable molecular tools. Thus, this mushroom is considered as a genomic orphan species with a very limited number of available molecular markers or sequences. To fill this gap, this study reports the generation and analysis of the first set of expressed sequence tags (EST) for A. subrufescens. cDNA fragments obtained from young sporophores (SP) and vegetative mycelium in liquid culture (CL) were sequenced using 454 pyrosequencing technology. After assembly process, 4,989 and 5,125 sequences were obtained in SP and CL libraries, respectively. About 87 % of the EST had significant similarity with Agaricus bisporus-predicted proteins, and 79 % correspond to known proteins. Functional categorization according to Gene Ontology could be assigned to 49 % of the sequences. Some gene families potentially involved in bioactive compound biosynthesis could be identified. A total of 232 simple sequence repeats (SSRs) were identified, and a set of 40 EST-SSR polymorphic markers were successfully developed. This EST dataset provides a new resource for gene discovery and molecular marker development. It constitutes a solid basis for further genetic and genomic studies in A. subrufescens.

International audience; The structure, homologies, polymorphism and expression profiles of a new gene, aap1, have been studied for precisely characterizing it and defining its putative involvement in thermo-tolerance of both vegetative mycelium growth and sporophore differentiation. Sequence polymorphism was analyzed in 3 homokaryons of A. bisporus and 24 strains having different abilities for mycelial growth at temperatures above 30°C and for producing mature fruiting bodies at 25°C. The level of gene expression was measured by real-time PCR both in vegetative mycelium after transfer from 25 to 32°C and in primordia and fruiting bodies produced during cultures at 17 or 25°C. The results indicated that aap1 gene belong to a new subfamily of the yeast YAP1 homologs. It is not a dominant contributor to the thermo-tolerance of A. bisporus, but the protein it encodes may be involved as an overall stress resistance transcription factor. The way Aap1 senses redox level differs from that of AP-1-like transcription factor Yap1.

The almond mushroom Agaricus subrufescens (formerly Agaricus blazei or Agaricus brasiliensis) is cultivated at commercial level in Brazil and some Asian countries on local substrates and casing mixtures. Despite its tropical origin, A. subrufescens might be a seasonal option for mushroom growers in western countries, where some wild strains have been isolated. For this purpose, cultivation conditions were developed starting from the substrate and casing mixture commonly used for commercial production of the button mushroom Agaricus bisporus in France.The commercial compost, based on wheat straw and horse manure, used for A. bisporus and the casing mixture (peat and limestone) supplemented with fine sand proved efficient to grow A. subrufescens. Increasing the depth of the casing layer improved significantly the yield and time to fruiting. Daily variations in temperature did not markedly modify the yield. Significantly higher mushroom biomass was obtained with three wild European strains compared with three Brazilian cultivars. The very productive wild strain CA438-A gave mushrooms of size and dry matter content comparable to those of a cultivar.Commercial production of A. subrufescens can be developed in western countries on the wheat straw-based substrate commonly used for A. bisporus in these regions, by a simple modification of the casing mixture and maintaining the incubation temperature throughout the crop, which is expected to save energy during summer. Good yields were obtained cultivating European strains under optimised parameters.

International audience; The Brazilian almond mushroom is currently cultivated for its medicinal properties but cultivars are suspected all to have a common origin. The objective of this work was to assess the potential of wild isolates of Agaricus subrufescens Peck (Agaricus blazei, Agaricus brasiliensis) as a source of new traits to improve the mushroom yield and quality for developing new cultures under European growing conditions. The wild European strains analysed showed a good ability to be commercially cultivated on wheat straw and horse manure based compost: shorter time to fruiting, higher yield, similar antioxidant activities when compared to cultivars. They have a valuable potential of genetic and phenotypic diversity and proved to be interfertile with the original culture of the Brazilian almond mushroom. Intercontinental hybrids could be obtained and combine properties from both Brazilian and European germplasm for increasing the choice of strains cultivated by the mushroom growers.

In the near future, the production of oilfields with high contents of associated sour gases will increase. Research on technologies to produce such fields are therefore of utmost importance. Due to the presence of corrosive gas, special attention has to be paid to the design of well materials (casing, cementing materials). However, published data on degradation mechanisms of cement-based materials exposed to H2S environments are very scarce. When placed in contact with acid fluid, portland cement will dissolve and become, at some time, fully degraded. In this case, the zonal isolation will be no more effective. New solutions are required to ensure long-term integrity of cementing materials. One potential solution is to incorporate chemicals in the cementitious matrix. The key idea is to incorporate additives that react preferentially with H2S and not with hydrated phases of the cement. The goal of this work was to assess this solution. The paper is dealing with cement formulations that incorporate mineral admixtures. These mineral admixtures have been chosen because of their high chemical affinity with hydrogen sulphide. We first give properties (density, compressive strength, rheological behaviour) of the novel formulations. Then we describe the static ageing tests performed in H2S-saturated brine at 120°C and 15 MPa. By combining different analytical techniques, the chemical evolution of the new formulations has been investigated. The results are dependent on the nature of the reactive mineral admixture. We show that, in some particular case, the incorporation of specific mineral admixtures leads to a strong damaging effect for the cement matrix. Consequently, for the design of H2S-resistant cement, these specific mineral admixtures should be discarded. The proposed solution (addition of reactive chemicals) is promising but requires more investigation in order to carefully control the reactivity of the different chemical species.