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This review provides an overview of the advances made with the Arabidopsis thaliana-Fusarium oxysporum5176 pathosystem in understanding the cause and defense against wilt disease in plants. Fusarium oxysporum is a soil-borne fungal pathogen of several major food crops. Research on understanding the molecular details of fungal infection and the plant's defense mechanisms against this pathogen has long focused mainly on the tomato-infecting F. oxysporum strains and their specific host plant. However, in recent years, the Arabidopsis thaliana-Fusarium oxysporum strain 5176 (Fo5176) pathosystem has additionally been established to study this plant-pathogen interaction with all the molecular biology, genetic, and genomic tools available for the A. thaliana model system. Work on this system has since produced several new insights, especially with regards to the role of phytohormones involved in the plant's defense response, and the receptor proteins and peptide ligands involved in pathogen detection. Furthermore, work with the pathogenic strain Fo5176 and the related endophytic strain Fo47 has demonstrated the suitability of this system for comparative studies of the plant's specific responses to general microbe- or pathogen-associated molecular patterns. In this review, we highlight the advantages of this specific pathosystem, summarize the advances made in studying the molecular details of this plant-fungus interaction, and point out open questions that remain to be answered.

ispartof: HORTICULTURAL PLANT JOURNAL vol:8 issue:3 pages:289-296 status: published

Strawberry cultivation is associated with high mineral fertilizer doses and extensive use of chemical plant protection products. Based on previous research, we expected that chitin application to peat substrate would increase the nutrient availability and activate the plant systemic defense response, resulting in higher strawberry yields and fewer disease symptoms. We set up two experiments in which the temporal variability and differences in initial nutrient concentrations of the growing media were taken into account. Chitin treatment resulted in the attraction of plant growth–promoting fungi toward the plant root, such as species from genera Mortierella and Umbelopsis. In addition, by the end of the experiments 87 mg of mineral nitrogen (N) per liter of substrate was mineralized, which can be related to the observed increase in plant shoot biomass. This, however, led to nutrient imbalances in plant shoots and fruit; N concentration in the leaves increased over 30%, exceeding the optimal range, while phosphorous (P) and potassium (K) deficiencies occurred, with concentrations lower than 50% of the optimal range. This may explain the decreased fruit yield and disease resistance of the fruit toward Botrytis cinerea. In contrast, chitin caused a clear defense priming effect in the strawberry leaves, with a strong induction of the jasmonic acid response, resulting in fewer foliar disease symptoms. Chitin causes positive effects on shoot growth and foliar disease resistance, but caution needs to be taken for nutrient imbalances leading to negative influences on root growth, fruit production, and disease susceptibility toward B. cinerea. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

This study was carried out to determine the antifungal activity of mint (Mentha piperita L.), thyme (Thymus vulgaris L.) and eucalyptus (Eucalyptus citriodora Hook.) essential oils against 4 different pathotypes of chickpea blight (Ascochyta rabiei) under in-vitro conditions. The antifungal activity assay was performed in 100 mm petri dishes containing 20 mL Potato-Dextrose-Agar (PDA) media. Essential oils were added to petri dishes containing autoclaved PDA medium in doses of 0.125, 0.25, 0.5, 1 and 2 mu L mL(-1). 5 mm diameter fungal discs were placed in the middle of petri dishes. PDA medium free of essential oils as negative control and as a positive control PDA media containing commercial fungicide %25.2 Boscalid+%12.8 Pyraclostrobin (BASF company) were used. Petri dishes sealed with para-film were incubated for 14 days at 22 +/- 1 degrees C. The experiment was conducted in a randomized plot design with three replications. Measurements were made after completion of the incubation period and percent inhibition of mycelial growth was determined. It was deteimined that mint essential oil completely inhibited mycelium growth of pathotype I, II and IV, by 100% and the effect was fungicidal at the positive control. The dose of 2 mu L mL(-1) and positive control inhibited mycelium growth of pathotype III, by 81.3% and 82.9% respectively. It was found that thyme essential oil completely inhibited mycelium growth of all pathotypes at the dose of 2 mu L mL(-1) and positive control inhibited mycelium growth of pathotypes I and III, by 100% and the effects was fungicidal. It was seen that eucalyptus essential oil completely inhibited mycelium growth of pathotypes II and. IV, by 100% and this effect was fungicidal at the positive control, The dose of 2 mu L mL(-1) and positive control had an effect of 84.9% and 84.1% against pathotype 1, 84,1% and 83.7% against pathotype III, respectively.

Feeding a rising population of currently 7.8 billion people globally requires efficient agriculture, which is preferably sustainable. Today, farmers are largely dependent on synthetic fungicides to avoid food losses caused by fungal diseases. However, the extensive use of these has resulted in the emergence of fungicide-resistant pathogens and concerns have been raised over the residual effects on the environment and human health. In this regard, biocontrol agents (BCAs) have been proposed as an alternative to standard fungicides but their disease management capacity is usually incomplete and heavily relies on uncontrollable environmental conditions. An integrated approach combining BCAs with fungicides, which is the focus of this review, is put forward as a way to reduce the fungicide doses to manage plant diseases and thereby their residue on harvested crops. In addition, such a strategy of combining antifungal treatments with different modes of action reduces the selection pressure on pathogens and thereby the chances of resistance development. However, to allow its large-scale implementation, further knowledge is needed, comprising timing, number and interval of repeated BCA applications and their compatibility with fungicides. The compatibility of BCAs with fungicides might differ when applied in a mixture or when used in alternation. ispartof: MICROORGANISMS vol:8 issue:12 ispartof: location:Switzerland status: published

Sporadic and unpredictable extreme hot weather events associated with global warming have been an increasingly serious problem and are difficult to test under natural field conditions. In this study, we used subtropical summer to mimic extreme hot weather under realistic field conditions to test for heat tolerance in the cold-adapted emergent oil crop, Camelina sativa. Utilizing a forward genetic screen, Camelina was screened for heat-adapted genotypes, resulting in the identification of three subtropical summer tolerant (sst) mutants. The sst mutants were late flowering and exhibited altered expression of the key flowering genes FLOWER LOCUS C and FLOWER LOCUS T. With RNA-seq assay, it was found that redox and defense related genes were significantly enriched in the up-regulated genes of the sst mutants. Consistently, reduced hydrogen peroxide production and enhanced resistance to a fungal pathogen were observed. Overall, our results suggested that to breed temperate crops to adapt to the subtropics, flowering time, antioxidant ability, and defense signaling could be the potential targets.

The expression of Vitis vinifera polygalacturonase inhibiting protein 1 (VviPGIP1) in Nicotiana tabacum has been linked to modifications at the cell wall level. Previous investigations have shown an upregulation of the lignin biosynthesis pathway and reorganisation of arabinoxyloglucan composition. This suggests cell wall tightening occurs, which may be linked to defence priming responses. The present study used a screening approach to test four VviPGIP1 and four NtCAD14 overexpressing transgenic lines for cell wall alterations. Overexpressing the tobacco-derived cinnamyl alcohol dehydrogenase (NtCAD14) gene is known to increase lignin biosynthesis and deposition. These lines, particularly PGIP1 expressing plants, have been shown to lead to a decrease in susceptibility towards grey rot fungus Botrytis cinerea. In this study the aim was to investigate the cell wall modulations that occurred prior to infection, which should highlight potential priming phenomena and phenotypes. Leaf lignin composition and relative concentration of constituent monolignols were evaluated using pyrolysis gas chromatography. Significant concentrations of lignin were deposited in the stems but not the leaves of NtCAD14 overexpressing plants. Furthermore, no significant changes in monolignol composition were found between transgenic and wild type plants. The polysaccharide modifications were quantified using gas chromatography (GC&ndash, MS) of constituent monosaccharides. The major leaf polysaccharide and cell wall protein components were evaluated using comprehensive microarray polymer profiling (CoMPP). The most significant changes appeared at the polysaccharide and protein level. The pectin fraction of the transgenic lines had subtle variations in patterning for methylesterification epitopes for both VviPGIP1 and NtCAD14 transgenic lines versus wild type. Pectin esterification levels have been linked to pathogen defence in the past. The most marked changes occurred in glycoprotein abundance for both the VviPGIP1 and NtCAD14 lines. Epitopes for arabinogalactan proteins (AGPs) and extensins were notably altered in transgenic NtCAD14 tobacco.

Wild tomato species represent a rich gene pool for numerous desirable traits lost during domestication. Here, we exploited an introgression population representing wild desert-adapted species and a domesticated cultivar to establish the genetic basis of gene expression and chemical variation accompanying the transfer of wild-species-associated fruit traits. Transcriptome and metabolome analysis of 580 lines coupled to pathogen sensitivity assays resulted in the identification of genomic loci associated with levels of hundreds of transcripts and metabolites. These associations occurred in hotspots representing coordinated perturbation of metabolic pathways and ripening-related processes. Here, we identify components of the Solanum alkaloid pathway, as well as genes and metabolites involved in pathogen defense and linking fungal resistance with changes in the fruit ripening regulatory network. Our results outline a framework for understanding metabolism and pathogen resistance during tomato fruit ripening and provide insights into key fruit quality traits., This project has received funding from the European Research Council (grant agreement 204575-SAMIT), EU Framework Program FP7/2007–2013 (grant agreement 613692-TriForC) and the Israel Science Foundation (grant number 1805/15). We thank the Adelis Foundation, Leona M. and Harry B. Helmsley Charitable Trust, Jeanne and Joseph Nissim Foundation for Life Sciences, Tom and Sondra Rykoff Family Foundation Research and Raymond Burton Plant Genome Research Fund for supporting A.A.’s laboratory activity. A.K. is thankful for a short-term EMBO fellowship (EMBO-ASTF-146-2014).

Summary The fungus Batrachochytrium dendrobatidis (Bd) causes chytridiomycosis, a lethal epizootic disease of amphibians. Rapid identification of the pathogen and biosecurity is essential to prevent its spread, but current laboratory‐based tests are time‐consuming and require specialist equipment. Here, we describe the generation of an IgM monoclonal antibody (mAb), 5C4, specific to Bd as well as the related salamander and newt pathogen Batrachochytrium salamandrivorans (Bsal). The mAb, which binds to a glycoprotein antigen present on the surface of zoospores, sporangia and zoosporangia, was used to develop a lateral‐flow assay (LFA) for rapid (15 min) detection of the pathogens. The LFA detects known lineages of Bd and also Bsal, as well as the closely related fungus Homolaphlyctis polyrhiza, but does not detect a wide range of related and unrelated fungi and oomycetes likely to be present in amphibian habitats. When combined with a simple swabbing procedure, the LFA was 100% accurate in detecting the water‐soluble 5C4 antigen present in skin, foot and pelvic samples from frogs, newts and salamanders naturally infected with Bd or Bsal. Our results demonstrate the potential of the portable LFA as a rapid qualitative assay for tracking these amphibian pathogens and as an adjunct test to nucleic acid‐based detection methods.

Grey mould, the most important disease of strawberry worldwide, is caused by Botrytis cinerea and a few additional Botrytis spp. Fungicide resistance is a growing problem and has become a limiting factor in strawberry production. In northern Germany, an annual survey of Botrytis isolates from commercial strawberry fields in 2010 to 2017 has revealed high (> 20%) frequencies of resistance to quinone-outside inhibitors, fenhexamid, boscalid, fludioxonil and cyprodinil, as well as lower (

Vitamin B6 (pyridoxine) is vital for key metabolic reactions and reported to have antioxidant properties in planta. Therefore, enhancement of vitamin B6 content has been hypothesized to be a route to improve resistance to biotic and abiotic stresses. Most of the current studies on vitamin B6 in plants are on eudicot species, with monocots remaining largely unexplored. In this study, we investigated vitamin B6 biosynthesis in rice, with a view to examining the feasibility and impact of enhancing vitamin B6 levels. Constitutive expression in rice of two Arabidopsis thaliana genes from the vitamin B6 biosynthesis de novo pathway, AtPDX1.1 and AtPDX2, resulted in a considerable increase in vitamin B6 in leaves (up to 28.3‐fold) and roots (up to 12‐fold), with minimal impact on general growth. Rice lines accumulating high levels of vitamin B6 did not display enhanced tolerance to abiotic stress (salt) or biotic stress (resistance to Xanthomonas oryzae infection). While a significant increase in vitamin B6 content could also be achieved in rice seeds (up to 3.1‐fold), the increase was largely due to its accumulation in seed coat and embryo tissues, with little enhancement observed in the endosperm. However, seed yield was affected in some vitamin B6‐enhanced lines. Notably, expression of the transgenes did not affect the expression of the endogenous rice PDX genes. Intriguingly, despite transgene expression in leaves and seeds, the corresponding proteins were only detectable in leaves and could not be observed in seeds, possibly pointing to a mode of regulation in this organ., The Plant Journal, 99 (6), ISSN:0960-7412, ISSN:1365-313X

Peat based growing media are not ecologically sustainable and often fail to support biological control. Miscanthus straw was (1) tested to partially replace peat; and (2) pre-colonized with a Trichoderma strain to increase the biological control capacity of the growing media. In two strawberry pot trials (denoted as experiment I & II), extruded and non-extruded miscanthus straw, with or without pre-colonization with T. harzianum T22, was used to partially (20% v/v) replace peat. We tested the performance of each mixture by monitoring strawberry plant development, nutrient content in the leaves and growing media, sensitivity of the fruit to the fungal pathogen Botrytis cinerea, rhizosphere community and strawberry defense responses. N immobilization by miscanthus straw reduced strawberry growth and yield in experiment II but not in I. The pre-colonization of the straw with Trichoderma increased the post-harvest disease suppressiveness against B. cinerea and changed the rhizosphere fungal microbiome in both experiments. In addition, defense-related genes were induced in experiment II. The use of miscanthus straw in growing media will reduce the demand for peat and close resource loops. Successful pre-colonization of this straw with biological control fungi will optimize crop cultivation, requiring fewer pesticide applications, which will benefit the environment and human health.

The Elongator complex (hereafter Elongator) promotes RNA polymerase II-mediated transcript elongation through epigenetic activities such as histone acetylation. Elongator regulates growth, development, immune response and sensitivity to drought and abscisic acid. We demonstrate that elo mutants exhibit defective hypocotyl elongation but have a normal apical hook in darkness and are hyposensitive to light during photomorphogenesis. These elo phenotypes are supported by transcriptome changes, including downregulation of circadian clock components, positive regulators of skoto- or photomorphogenesis, hormonal pathways and cell wall biogenesis-related factors. The downregulated genes LHY, HFR1 and HYH are selectively targeted by Elongator for histone H3K14 acetylation in darkness. The role of Elongator in early seedling development in darkness and light is supported by hypocotyl phenotypes of mutants defective in components of the gene network regulated by Elongator, and by double mutants between elo and mutants in light or darkness signaling components. A model is proposed in which Elongator represses the plant immune response and promotes hypocotyl elongation and photomorphogenesis via transcriptional control of positive photomorphogenesis regulators and a growth-regulatory network that converges on genes involved in cell wall biogenesis and hormone signaling., The research was funded by the EC Marie Curie Intra European fellowship (FP7 People: Marie-Curie Actions; FP7-PEOPLE-2010-IEF-273068) (LightEr) to M.W.; the Initial Research Training network FP7-PEOPLE-2013-ITN-607880 (CHIP-ET) to M.V.L., P.M. and fellows S.L.G. and J.F.; IWT predoctoral fellowship to S.L.G; and Fonds Wetenschappelijk Onderzoek (FWO) (G.0656.13N) to D.V.D.S.

Abiotic and biotic stress factors are the major constrains for the realization of crop yield potential. As climate change progresses, the spread and intensity of abiotic as well as biotic stressors is expected to increase, with increased probability of crops being exposed to both types of stress. Shielding crops from combinatorial stress requires a better understanding of the plant’s response and its genetic architecture. In this study, we evaluated resistance to salt stress, powdery mildew and to both stresses combined in tomato, using the Solanum habrochaites LYC4 introgression line (IL) population. The IL population segregated for both salt stress tolerance and powdery mildew resistance. Using SNP array marker data, QTLs were identified for salt tolerance as well as Na+ and Cl− accumulation. Salt stress increased the susceptibility of the population to powdery mildew in an additive manner. Phenotypic variation for disease resistance was reduced under combined stress as indicated by the coefficient of variation. No correlation was found between disease resistance and Na+ and Cl− accumulation under combined stress Most genetic loci were specific for either salt stress tolerance or powdery mildew resistance. These findings increase our understanding of the genetic regulation of responses to abiotic and biotic stress combinations and can provide leads to more efficiently breeding tomatoes and other crops with a high level of disease resistance while maintaining their performance in combination with abiotic stress.

Steroid hormones, botrydial, and inorganic ions were studied from cold and hot tap water samples with capillary electrophoresis techniques using UV detection. Identification of the steroids and botrydial was made with ultra-high -performance liquid chromatography (UHPLC) coupled to electrospray ionization orbitrap high-resolution mass spectrometry. Solid phase extraction with nonpolar and ion-exchange sorbents was needed to enrich the compounds for CE and UHPLC studies. The steroids identified from the drinking water samples were estradiol glucoside, androstenedione, testosterone, and progesterone. However, only progesterone could be quantified in both cold and hot tap water samples from Helsinki households. Its concentration varied from 0.031 ng/L to 0.135 ng/L and from 0.054 ng/L to 0.191 ng/L, respectively. Chloride and nitrate amounts were 25 mg/L. Calcium, potassium, magnesium, and sodium were 20, 1, 1, and 17 mg/L at the highest, respectively. Copper, iron, sulphate, and ammonium were below the methods concentration limits. Botrydial from Botrytis cinerea mould was identified in all drinking waters. In both cold and hot tap waters its concentration was 861-3900% higher than in a drilled well water that was also used as the household tap water. The mould was also confirmed by identification of its metabolite abscisic acid. (C) 2017 Elsevier B.V. All rights reserved.

Special Issue: 70 years of SPPS – Outlook by Early-Career PIs Plants live in a world where they are challenged by abiotic and biotic stresses. In response to unfavorable conditions or an acute challenge like a pathogen attack, plants use various signaling pathways that regulate expression of defense genes and other mechanisms to provide resistance or stress adaptation. Identification of the regulatory steps in defense signaling has seen much progress in recent years. Many of the identified signaling pathways show interactions with each other, exemplified by the modulation of the jasmonic acid response by salicylic acid. Accordingly, defense regulation is more appropriately thought of as a web of interactions, rather than linear pathways. Here we describe various regulatory components and how they interact to provide an appropriate defense response. One of the common assays to monitor the output of defense signaling, as well as interaction between signaling pathways, is the measurement of altered gene expression. We illustrate that, while this is a suitable assay to monitor defense regulation, it can also inadvertently provide overstated conclusions about interaction among signaling pathways.

International audience; Bêta-Aminobutyric acid (BABA) is a nonprotein amino acid inducing resistance in many different plant species against a wide range of abiotic and biotic stresses. Nevertheless, how BABA primes plant natural defense reactions remains poorly understood. Based on its structure, we hypothesized and confirmed that BABA is able to chelate iron (Fe) in vitro. In vivo, we showed that it led to a transient Fe deficiency response in Arabidopsis thaliana plants exemplified by a reduction of ferritin accumulation and disturbances in the expression of genes related to Fe homeostasis. This response was not correlated to changes in Fe concentrations, suggesting that BABA affects the availability or the distribution of Fe rather than its assimilation. The phenotype of BABA-treated plants was similar to those of plants cultivated in Fe-deficient conditions. A metabolomic analysis indicated that both BABA and Fe deficiency induced the accumulation of common metabolites, including p-couma-roylagmatine, a metabolite previously shown to be synthesized in several plant species facing pathogen attack. Finally, we showed that the protective effect induced by BABA against Botrytis cinerea was mimicked by Fe deficiency. In conclusion, the Fe deficiency response caused by BABA could bring the plant to a defense-ready state, participating in the plant resistance against the pathogens.

Like their animal counterparts, plant glutamate receptor-like (GLR) homologs are intimately associated with Ca(2+) influx through plasma membrane and participate in various physiological processes. In pathogen-associated molecular patterns (PAMP)-/elicitor-mediated resistance, Ca(2+) fluxes are necessary for activating downstream signaling events related to plant defense. In this study, oligogalacturonides (OGs), which are endogenous elicitors derived from cell wall degradation, were used to investigate the role of Arabidopsis GLRs in defense signaling. Pharmacological investigations indicated that GLRs are partly involved in free cytosolic [Ca(2+)] ([Ca(2+)]cyt) variations, nitric oxide (NO) production, reactive oxygen species (ROS) production and expression of defense-related genes by OGs. In addition, wild-type Col-0 plants treated with the glutamate-receptor antagonist 6,7-dinitriquinoxaline-2,3-dione (DNQX) had a compromised resistance to Botrytis cinerea and Hyaloperonospora arabidopsidis. Moreover, we provide genetic evidence that AtGLR3.3 is a key component of resistance against H. arabidopsidis. In addition, some OGs-triggered immune events such as defense gene expression, NO and ROS production are also to different extents dependent on AtGLR3.3. Taken together, these data provide evidence for the involvement of GLRs in elicitor/pathogen-mediated plant defense signaling pathways in Arabidopsis thaliana.

International audience; The effects of different anthropic activities (vineyard: phytosanitary protection; winery: pressing and sulfiting) on the fungal populations of grape berries were studied. The global diversity of fungal populations (moulds and yeasts) was performed by pyrosequencing. The anthropic activities studied modified fungal diversity. Thus, a decrease in biodiversity was measured for three successive vintages for the grapes of the plot cultivated with Organic protection compared to plots treated with Conventional and Ecophyto protections. The fungal populations were then considerably modified by the pressing-clarification step. The addition of sulfur dioxide also modified population dynamics and favoured the domination of the species Saccharomyces cerevisiae during fermentation. The non-targeted chemical analysis of musts and wines by FT-ICR-MS showed that the wines could be discriminated at the end of alcoholic fermentation as a function of adding SO2 or not, but also and above all as a function of phytosanitary protection, regardless of whether these fermentations took place in the presence of SO2 or not. Thus, the existence of signatures in wines of chemical diversity and microbiology linked to vineyard protection has been highlighted.

Endophytic Pseudomonas aeruginosa strain BP35 was originally isolated from black pepper grown in the rain forest in Kerala, India. Strain PaBP35 was shown to provide significant protection to black pepper against infections by Phytophthora capsici and Radopholus similis. For registration and implementation in disease management programmes, several traits of PaBP35 were investigated including its endophytic behaviour, biocontrol activity, phylogeny and toxicity to mammals. The results showed that PaBP35 efficiently colonized black pepper shoots and displayed a typical spatiotemporal pattern in its endophytic movement with concomitant suppression of Phytophthora rot. Confocal laser scanning microscopy revealed high populations of PaBP35::gfp2 inside tomato plantlets, supporting its endophytic behaviour in other plant species. Polyphasic approaches to genotype PaBP35, including BOX-PCR, recN sequence analysis, multilocus sequence typing and comparative genome hybridization analysis, revealed its uniqueness among P.¿aeruginosa strains representing clinical habitats. However, like other P.¿aeruginosa strains, PaBP35 exhibited resistance to antibiotics, grew at 25–41°C and produced rhamnolipids and phenazines. PaBP35 displayed strong type II secretion effectors-mediated cytotoxicity on mammalian A549 cells. Coupled with pathogenicity in a murine airway infection model, we conclude that this plant endophytic strain is as virulent as clinical P.¿aeruginosa strains. Safety issues related to the selection of plant endophytic bacteria for crop protection are discussed.

Cuticular defects trigger a battery of reactions including enhanced reactive oxygen species (ROS) production and resistance to necrotrophic pathogens. However, the source of ROS generated by such impaired cuticles has remained elusive. Here, we report the characterization of Arabidopsis thaliana ohyl mutant, a Peroxidase 57 (PER57) - overexpressing line that demonstrates enhanced defense responses that result both from increased accumulation of ROS and permeability of the leaf cuticle. The ohyl mutant was identified in a screen of A. thaliana seedlings for oligogalacturonides (OGs) insensitive/hypersensitive mutants that exhibit altered growth retardation in response to exogenous OGs. Mutants impaired in OG sensitivity were analyzed for disease resistance/susceptibility to the necrotrophic phytopathogens Botrytis cinerea and Pectobacterium carotovorum. In the ohyl line, the hypersensitivity to OGs was associated with resistance to the tested pathogens. This PER57 overexpressing line exhibited a significantly more permeable leaf cuticle than wild-type plants and this phenotype could be recapitulated by overexpressing other class III peroxidases. Such peroxidase overexpression was accompanied by the suppressed expression of cutin biosynthesis genes and the enhanced expression of genes associated with OG-signaling. Application of ABA completely removed ROS, restored the expression of genes associated with cuticle biosynthesis and led to decreased permeability of the leaf cuticle, and finally, abolished immunity to B. cinerea. Our work demonstrates that increased peroxidase activity increases permeability of the leaf cuticle. The loss of cuticle integrity primes plant defenses to necrotrophic pathogens via the activation of DAMP-responses.

Botrytis cinerea Pers.:Fr. is a major plant pathogen and a new approach is needed for its control in strawberry to minimise the increasing use of synthetic fungicides. The biofungicide Prestop-Mix, which contains Gliocladium catenulatum, is effective against Botrytis infections; however, the need for frequent applications increases the costs for farmers. Here, we demonstrate that bumble bees, Bombus terrestris L., effectively disseminate the preparation onto flowers in open field conditions. Over the course of three years, we found a highly significant decrease in the rate of Botrytis infection. Pathogen control was achieved with relatively low numbers of G. catenulatum spores per flower, even using flowers that are not highly attractive to bumble bees. An even distribution of spores was detected up to 100 m from the hives, either due to primary inoculation by bumble bees or secondary distribution by other flower visitors such as honey bees and solitary bees. We showed that the application of a biocontrol agent by bumble bees is reliable for the use of environmentally friendly pest control strategies in northern climatic conditions. This low cost technology is especially relevant for organic farming. This study provides valuable information for introducing this method into practice in open strawberry fields.

Reduced levels of trienoic fatty acids (TAs) in chloroplast membranes induce thermotolerance in several plant species, but the underlying mechanisms remain unclear. TA peroxidation in plant cell membranes generates cytotoxic, TA-derived compounds containing alpha,beta-unsaturated carbonyl groups. The relationship between low TA levels and the amounts of cytotoxic TA-derived compounds was examined using thermotolerant transgenic cyclamen (Cyclamen persicum Mill.) with low TA contents. Changes in the levels of the cytotoxic TA-derived acrolein (ACR), methyl vinyl ketone (MVK), (E)-2-hexenal, 4-hydroxy-2-nonenal, and malondialdehyde were analysed in the leaf tissues of wild-type (WT) and thermotolerant transgenic cyclamen under heat stress. Levels of ACR and MVK in the WT increased in parallel with the occurrence of heat-induced tissue damage, whereas no such changes were observed in the thermotolerant transgenic lines. Furthermore, exogenous ACR and MVK infiltrated into leaves to concentrations similar to those observed in heat-stressed WT leaves caused similar disease symptoms. These results suggest that thermotolerance in transgenic cyclamen depends on reduced production rates of ACR and MVK under heat stress, due to the low level of TAs in these plants. Ministry of Education, Science and Culture of Japan/211114002 BRAIN

Chemical control of Septoria leaf blotch, caused by Mycosphaerella graminicola, is essential to ensure wheat yield and food security in most European countries. Mycosphaerella graminicola has developed resistance to several classes of fungicide and, with the efficacy of azoles gradually declining over time, new modes of action and/or improvements in host varietal resistance are urgently needed to ensure future sustainable disease control. Several new-generation carboxamide fungicides with broad-spectrum activity have recently been introduced into the cereal market. Carboxamides inhibit succinate dehydrogenase (Sdh) of the mitochondrial respiratory chain (complex II) but, because of their single-site specificity, these fungicides may be prone to resistance development. The objective of this study was to assess the risk of resistance development to different Sdh inhibitor (SDHI) fungicides in M. graminicola. UV mutagenesis was conducted to obtain a library of carboxin-resistant mutants. A range of SDHI resistance-conferring mutations was found in Sdh subunits B, C and D. Pathogenicity studies with a range of Sdh variants did not detect any fitness costs associated with these mutations. Most of the amino acid residues identified (e.g. B-S221P/T, B-H267F/L/N/Y, B-I269V and D-D129E/G/T) are directly involved in forming the cavity in which SDHI fungicides bind. Docking studies of SDHI fungicides in structural models of wild-type and mutated Sdh complexes also indicated which residues were important for the binding of different SDHI fungicides and showed a different binding for fluopyram. The predictive power of the model was also shown. Further diagnostic development, enabling the detection of resistant alleles at low frequencies, and cross-resistance studies will aid the implementation of anti-resistance strategies to prolong the cost-effectiveness and lifetime of SDHI fungicides.

Plant-pathogenic fungi employ a variety of infection strategies; as a result, fungi probably rely on different sets of proteins for successful infection. The F-box protein Frp1, only present in filamentous fungi belonging to the Sordariomycetes, Leotiomycetes and Dothideomycetes, is required for nonsugar carbon catabolism and pathogenicity in the root-infecting fungus Fusarium oxysporum. To assess the role of Frp1 in other plant-pathogenic fungi, FRP1 deletion mutants were generated in Fusarium graminearum and Botrytis cinerea, and their phenotypes were analysed. Deletion of FgFRP1 in F. graminearum led to impaired infection of barley roots, but not of aerial plant parts. Deletion of BcFRP1 in B. cinerea did not show any effect on pathogenicity. Sexual reproduction, however, was impaired in both F. graminearum and B. cinerea FRP1 deletion mutants. The mutants of all three fungi displayed different phenotypes when grown on an array of carbon sources. The F. oxysporum and B. cinerea deletion mutants showed opposite growth phenotypes on sugar and nonsugar carbon sources. Replacement of FoFRP1 in F. oxysporum with the B. cinerea BcFRP1 resulted in the restoration of pathogenicity, but also in a switch from impaired growth on nonsugar carbon sources to impaired growth on sugar carbon sources. This effect could be ascribed in part to the B. cinerea BcFRP1 promoter sequence. In conclusion, the function of the F-box protein Frp1, despite its high sequence conservation, is not conserved between different fungi, leading to differential requirements for pathogenicity and carbon source utilization.

The development of new biocontrol products against plant diseases requires screening of high numbers of candidate antagonists. Antagonists for commercial use have to fulfill many different requirements. Besides being active against the specific targeted plant pathogens they must be safe and cost-effective. Important criteria besides pathogenic efficacy are market size, ecological characteristics, production costs, safety, environmental risks, and possibilities for intellectual property protection. A stepwise screening program considering these very different aspects is proposed. Research highlights ¿ Stepwise screening of microorganisms for commercial use in biocontrol. ¿ Multi-disciplinary approach considering many aspects besides control efficacy. ¿ Examples for protocols for use in screening programmes illustrating this approach. Article Outline 1. Introduction 2. Screening steps 2.1. Step 1: Assessment of targeted crop, disease and markets 2.2. Step 2: Origin and isolation of candidate antagonists 2.3. Step 3: Preliminary assessments in rapid-throughput screening systems 2.4. Step 4: Identification of candidate antagonists and database mining 2.5. Step 5: Efficacy testing against pathogens on plants 2.6. Step 6: Preliminary tests on mass production 2.7. Step 7: Development and testing of a pilot formulation and estimation of registration costs 2.8. Step 8: Field testing and upscaling mass production 2.9. Step 9: Integration into cropping systems Discussion

Parthenocarpy is the development of the fruit in absence of pollination and/or fertilization. In tomato, parthenocarpy is considered as an attractive trait to solve the problems of fruit setting under unfavorable conditions. We studied the genetics of parthenocarpy in two different lines, IL5-1 and IVT-line 1, both carrying Solanum habrochaites chromosome segments. Parthenocarpy in IL5-1 is under the control of two QTLs, one on chromosome 4 (pat4.1) and one on chromosome 5 (pat5.1). IVT-line 1 also contains two parthenocarpy QTLs, one on chromosome 4 (pat4.2) and one on chromosome 9 (pat9.1). In addition, we identified one stigma exsertion locus in IL5-1, located on the long arm of chromosome 5 (se5.1). It is likely that pat4.1, from IL5-1 and pat4.2, from IVT-line 1, both located near the centromere of chromosome 4 are allelic. By making use of the microsynteny between tomato and Arabidopsis in this genetic region, we identified ARF8 as a potential candidate gene for these two QTLs. ARF8 is known to act as an inhibitor for further carpel development in Arabidopsis, in absence of pollination/fertilization. Expression of an aberrant form of the Arabidopsis ARF8 gene, in tomato, has been found to cause parthenocarpy. This candidate gene approach may lead to the first isolation of a parthenocarpy gene in tomato and will allow further use in several crop species.

For the soybean pathogen Phytophthora sojae , chemotaxis of zoospores to isoflavones is believed to be critical for recognition of the host and for initiating infection. However, the molecular mechanisms underlying this chemotaxis are largely unknown. To investigate the role of G-protein and calcium signaling in chemotaxis, we analyzed the expression of several genes known to be involved in these pathways and selected one that was specifically expressed in sporangia and zoospores but not in mycelium. This gene, named PsGPA1 , is a single-copy gene in P. sojae and encodes a G-protein α subunit that shares 96% identity in amino acid sequence with that of Phytophthora infestans . To elucidate the function, expression of PsGPA1 was silenced by introducing antisense constructs into P. sojae. PsGPA1 silencing did not disturb hyphal growth or sporulation but severely affected zoospore behavior, including chemotaxis to the soybean isoflavone daidzein. Zoospore encystment and cyst germination were also altered, resulting in the inability of the PsGPA1 -silenced mutants to infect soybean. In addition, the expressions of a calmodulin gene, PsCAM1 , and two calcium- and calmodulin-dependent protein kinase genes, PsCMK3 and PsCMK4 , were increased in the mutant zoospores, suggesting that PsGPA1 negatively regulates the calcium signaling pathways that are likely involved in zoospore chemotaxis.

International audience; Cell wall hemicelluloses and pectins are O-acetylated at specific positions, but the significance of these substitutions is poorly understood. Using a transgenic approach, we investigated how reducing the extent of O-acetylation in xylan affects cell wall chemistry, plant performance and the recalcitrance of lignocellulose to saccharification. The Aspergillus niger acetyl xylan esterase AnAXE1 was expressed in Arabidopsis under the control of either the constitutively expressed 35S CAMV promoter or a woody-tissue-specific GT43B aspen promoter, and the protein was targeted to the apoplast by its native signal peptide, resulting in elevated acetyl esterase activity in soluble and wall-bound protein extracts and reduced xylan acetylation. No significant alterations in cell wall composition were observed in the transgenic lines, but their xylans were more easily digested by a beta-1,4-endoxylanase, and more readily extracted by hot water, acids or alkali. Enzymatic saccharification of lignocellulose after hot water and alkali pretreatments produced up to 20% more reducing sugars in several lines. Fermentation by Trametes versicolor of tissue hydrolysates from the line with a 30% reduction in acetyl content yielded similar to 70% more ethanol compared with wild type. Plants expressing 35S: AnAXE1 and pGT43B:AnAXE1 developed normally and showed increased resistance to the biotrophic pathogen Hyaloperonospora arabidopsidis, probably due to constitutive activation of defence pathways. However, unintended changes in xyloglucan and pectin acetylation were only observed in 35S: AnAXE1-expressing plants. This study demonstrates that postsynthetic xylan deacetylation in woody tissues is a promising strategy for optimizing lignocellulosic biomass for biofuel production.

The objective of this work was to investigate possible modes of action of the yeast Cryptococcus magnus in controlling anthracnose (Colletotrichum gloeosporioides) on post harvested papaya fruits. Scanning electron microscopy was used to analyze the effect of the yeast on inoculations done after harvest. Results showed that C. magnus is able to colonize wound surfaces much faster than the pathogen, outcompeting the later for space and probably for nutrients. In addition, C. magnus produces a flocculent matrix, which affects hyphae integrity. The competition for space and the production of substances that affect hyphae integrity are among the most important modes of action of this yeast

Medical drugs known to modulate the activity of human ATP-binding cassette (ABC) transporter proteins (modulators) were tested for the ability to potentiate the activity of the azole fungicide cyproconazole against in vitro growth of Mycosphaerella graminicola and to control disease development due to this pathogen on wheat seedlings. In vitro modulation of cyproconazole activity could be demonstrated in paper disk bioassays. Some of the active modulators (amitriptyline, flavanone, and phenothiazines) increased the accumulation of cyproconazole in M. graminicola , suggesting that they reversed cyproconazole efflux. However, synergism between cyproconazole and modulators against M. graminicola on wheat seedlings could not be shown. Despite their low in vitro toxicity to M. graminicola , some modulators (amitriptyline, loperamide, and promazine) did show significant intrinsic disease control activity in preventive and curative foliar spray tests with wheat seedlings. The results suggest that these compounds have indirect disease control activity based on modulation of fungal ABC transporters essential for virulence and constitute a new class of disease control agents.

International audience; There have been many reviews concerned with antimicrobial food packaging, and with the use of antifungal compounds, but none provided an exhaustive picture of the applications of active packaging to control fungal spoilage. Very recently, many studies have been done in these fields, therefore it is timely to review this topic. This article examines the effects of essential oils, preservatives, natural products, chemical fungicides, nanopartides coated to different films, and chitosan in vitro on the growth of moulds, but also in vivo on the mould free shelf-life of bread, cheese, and fresh fruits and vegetables. A short section is also dedicated to yeasts. All the applications are described from a microbiological point of view, and these were sorted depending on the name of the species. Methods and results obtained are discussed. Essential oils and preservatives were ranked by increased efficacy on mould growth. For all the tested molecules, Penicillium species were shown more sensitive than Aspergillus species. However, comparison between the results was difficult because it appeared that the efficiency of active packaging depended greatly on the environmental factors of food such as water activity, pH, temperature, NaCl concentration, the nature, the size, and the mode of application of the films, in addition to the fact that the amount of released antifungal compounds was not constant with time.

A flexible model for biological control of a plant pathogen affecting host flowers is developed which takes into account the transfer of both the plant pathogen and the biological control agent (BCA) from the leaves to flowers. Because flowers, other than in ornamental plants, are largely ephemeral, the emphasis in analysis is on the rates of transfer and establishment on flowers. The form of the model analysed depends upon: the pattern of flowering for a particular host plant, a single instantaneous flush or continuous seasonal production; the effect of flowering phenology and morphology on transfer of both the pathogen and BCA; and the transient dynamics of such transfer. In the case of a single instantaneous flush, the relative importance of mycoparasitism and competition in protecting flowers during their short period of blooming is assessed. Where flowering is continuous but transfer lags behind because of floral phenology or morphology, a comparison is made between the initial levels of the pathogen and the BCA as they transfer to the flowers, depending again on the relative contribution of mycoparasitism and competition over the extended period of blooming. Differential rates of transfer of the pathogen and the BCA, depending on their time-dependent population densities on leaves, have a major impact on eventual biocontrol outcomes. The model results are used to analyse biocontrol strategies for contrasting host-pathogen systems which show different flowering patterns and biological control mechanisms. For Erwinia amylovora causing fireblight in pome fruit trees, an inundative biocontrol strategy targeting flowers is supported. In Botrytis cinerea, there is considerable potential for a strategy based on the establishment of BCAs on leaves for some of the plant hosts affected.

Host cells use an intricate signaling system to respond to invasions by pathogenic microorganisms. Although several signaling components of disease resistance against necrotrophic fungal pathogens have been identified, our understanding for how molecular components and host processes contribute to plant disease susceptibility is rather sparse. Here, we identified four transcription factors (TFs) from Arabidopsis that limit pathogen spread. Arabidopsis mutants defective in any of these TFs displayed increased disease susceptibility to Botrytis cinerea and Plectosphaerella cucumerina, and a general activation of non-immune host processes that contribute to plant disease susceptibility. Transcriptome analyses revealed that the mutants share a common transcriptional signature of 77 up-regulated genes. We characterized several of the up-regulated genes that encode peptides with a secretion signal, which we named PROVIR (for provirulence) factors. Forward and reverse genetic analyses revealed that many of the PROVIRs are important for disease susceptibility of the host to fungal necrotrophs. The TFs and PROVIRs identified in our work thus represent novel genetic determinants for plant disease susceptibility to necrotrophic fungal pathogens., Author Summary Diseases caused by pathogens affect most plants in their natural environment. Plants combat the majority of these intruders by activating elaborate immune responses, which typically result in a disease resistance response. Nevertheless, pathogens have typically evolved ways to bypass plant defenses, and susceptibility to pathogens re-appears. In addition to this occasional immune failure of the host, other immune-response independent processes allow further ingress of the invading pathogen, and contribute to plant pathogen susceptibility. We identified four transcription factors (TFs) that are required for effective disease resistance to fungal necrotrophs. These TFs regulate critical aspects of disease resistance/susceptibility to necrotrophs without interfering with immune signaling. Mutant plants defective in any of these four TFs commonly induce about 80 genes, with a substantial proportion encoding peptides with secretion signals that are described to act as local signals (peptide hormones) during cell-to-cell communication, and that function in the plant-specific paracrine/autocrine system. We further show that many of these peptide hormones affect disease susceptibility of the host to necrotrophs. Our findings have thus uncovered many new factors that underpin immune-response independent processes of plant disease susceptibility.

The effect of inoculations with yeasts occurring on apple surfaces and fungicide treatments on the russeting of Elstar apples was studied. Captan, dithianon and a water treatment were implemented to study the interaction between the fungicides, the inoculated yeast species and Aureobasidium pullulans, and the development of russet. All yeast inoculations aggravated russet, but Rhodotorula glutinis, Sporidiobolus pararoseus and A. pullulans did so to a greater extent than the other species. Both captan and dithianon significantly reduced russeting. Denaturing gradient gel electrophoresis analysis showed that inoculations with R. glutinis and S. pararoseus seemed to suppress other yeast species present on the apple surface.

SUMMARY Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic fungal pathogen causing disease in a wide range of plants. This review summarizes current knowledge of mechanisms employed by the fungus to parasitize its host with emphasis on biology, physiology and molecular aspects of pathogenicity. In addition, current tools for research and strategies to combat S. sclerotiorum are discussed.Sclerotinia sclerotiorum (Lib.) de Bary: kingdom Fungi, phylum Ascomycota, class Discomycetes, order Helotiales, family Sclerotiniaceae, genus Sclerotinia.Hyphae are hyaline, septate, branched and multinucleate. Mycelium may appear white to tan in culture and in planta. No asexual conidia are produced. Long-term survival is mediated through the sclerotium; a pigmented, multi-hyphal structure that can remain viable over long periods of time under unfavourable conditions for growth. Sclerotia can germinate to produce mycelia or apothecia depending on environmental conditions. Apothecia produce ascospores, which are the primary means of infection in most host plants.S. sclerotiorum is capable of colonizing over 400 plant species found worldwide. The majority of these species are dicotyledonous, although a number of agriculturally significant monocotyledonous plants are also hosts. Disease symptoms: Leaves usually have water-soaked lesions that expand rapidly and move down the petiole into the stem. Infected stems of some species will first develop dark lesions whereas the initial indication in other hosts is the appearance of water-soaked stem lesions. Lesions usually develop into necrotic tissues that subsequently develop patches of fluffy white mycelium, often with sclerotia, which is the most obvious sign of plants infected with S. sclerotiorum.http://www.whitemoldresearch.com; http://www.broad.mit.edu/annotation/fungi/sclerotinia_sclerotiorum.

Complete inhibition of the germination of spores of Botrytis cinerea occurred after a 10 s exposure to 30% ethanol or more at 24degreesC. Mortality of spores in heated 10% ethanol was higher than in water at the same temperatures. Immersion of naturally infected, freshly harvested table grapes for 30 s in 30% ethanol at 24 degreesC reduced decay approximately 50% after 35 days of storage at 1 degreesC. The addition of ethanol significantly improved the efficacy of a hot water treatment applied to grapes that were inoculated with B. cinerea two hours prior to immersion in heated solutions. Immersion of inoculated, freshly harvested table grapes for 3 min at 30, 40, or 50 degreesC in 10% ethanol reduced decay to 20.7, 6.7, and 0.1 berries/kg after 30 days of storage at 1 degreesC, while decay after immersion in water at these temperatures was 35.9, 17.6, and 1.7 berries/kg, respectively. Immersion for 30 or 60 s at 50, 55, or 60 degreesC in water or 10% ethanol also significantly reduced the number of decayed berries that developed after storage for 30 days at 1 degreesC. The appearance of the rachis and berries, incidence of cracked berries, flesh browning, flavor, weight loss, and berry color were examined and most treatments did not adversely affect these quality parameters. Prompt drying of the fruit after treatment was important to prevent berry cracking.

The yeast Metschnikowia fructicola was tested as a preharvest treatment to control preharvest and postharvest rots of strawberry fruit in Turkey and Israel. In greenhouse trials, the efficacy of the yeast antagonist against preharvest rots was equal to that of a chemical control (fenhexamid) in two growing seasons. In an open-field experiment, the yeast reduced the incidence of rot to commercially acceptable levels. M. fructicola reduced the incidence of fruit rot by 56-69% in greenhouses, open-field culture, and in low plastic tunnels. The yeast suppressed postharvest incidence of fruit rot significantly better than fenhexamid. Among fruit from greenhouses, open-field culture, or tunnels, M. fructicola treatment reduced the incidence of fruit rot during postharvest storage by 70, 64, and 72%, respectively. When applied weekly in the greenhouse or in the field, the population density of M. fructicola was about 1 x 10(5) cfu/fruit. Similar population density of the antagonist was also observed during storage of the fruit at 0 degrees.

FEMS Microbiology Reviews, 39 (2), ISSN:0168-6445, ISSN:1574-6976

Previous studies have identified the Arabidopsis thaliana transcription factor WRKY70 as a node of convergence for salicylic acid (SA) and jasmonic acid (JA)-mediated defense signal pathways and, together with its closest homolog WRKY54, as a negative regulator of SA biosynthesis. Here, we demonstrate that WRKY70 together with WRKY54 negatively affect the response of Arabidopsis to the necrotrophic pathogens Pectobacterium carotovorum and Botrytis cinerea, but not to the hemibiotroph Pseudomonas syringae pv tomato (Pst) DC3000, as revealed by mutants studies. Unstressed wrky54wrky70 double mutants exhibited increased levels of SA, accumulation of hydrogen peroxide (H2O2) and up-regulated expression of both SA and JA/ethylene (ET) responsive defense related genes. Additionally, protein cross-linking in cell wall was promoted by endogenous SA, suggesting involvement of wall-associated defenses against necrotrophs. This response to necrotrophs was compromised by introducing the sid2-1 allele impairing SA biosynthesis and leading to reduction of H2O2 content and of defense gene expression. The data suggest that the elevated SA level in the wrky54wrky70 double mutant results in moderate accumulation of H2O2, in promoting cell wall fortification and consequently enhanced resistance to necrotrophs but is not sufficient to trigger hypersensitive reaction (HR)-like cell death and resistance to biotrophs/hemibiotrophs like Pst DC3000.

International audience; The non-protein amino acid b-aminobutyric acid (BABA) protects the plant against various pathogens. Until now, this protection was described to involve the priming of pathogen-specific defence responses but a direct fungicidal effect was excluded. The present study shows that BABA inhibited mycelial growth and germination of the necrotrophic fungus Botrytis cinerea and affected Saccharomyces cerevisiae growth in a concentration-dependent manner. Variations of the fungicidal action at acidic pH and between different strains were observed.

Plant immunity is activated through complex and cross-talking transduction pathways that include a mitogen-activated protein kinase phosphorylation cascade. Here, we have investigated the role in immunity of the Arabidopsis (Arabidopsis thaliana) gene subfamily that encodes the mitogen-activated protein triple kinases indicated as ARABIDOPSIS NUCLEUS- AND PHRAGMOPLAST-LOCALIZED KINASE1-RELATED PROTEIN KINASE1 (ANP1), ANP2, and ANP3. For this study, we used representative danger signals (elicitors) belonging to the classes of the damage- and pathogen-associated molecular patterns, i.e. oligogalacturonides, linear fragments derived from the plant cell wall homogalacturonan, and the peptide elf18 derived from the bacterial elongation factor thermo-unstable. Analyses of single and double as well as conditional triple mutants show that ANPs are required for elicitor-triggered defense responses and protection against the necrotrophic fungus Botrytis cinerea. Notably, ANPs are also required for both the elicitor-induced oxidative burst and the transduction of the hydrogen peroxide signal but not for the inhibition of auxin-induced gene expression, indicating that this response can be uncoupled from the activation of defense responses. Our findings point to ANPs as key transduction elements that coordinate damage- and pathogen-associated molecular pattern-triggered immunity and orchestrate reactive oxygen species accumulation and signaling.

Resistance of Alternaria alternata to boscalid, the first succinate dehydrogenase inhibitor (SDHI) fungicide labeled on pistachio, has become a common occurrence in California pistachio orchards and affects the performance of this fungicide. In this study, we established the baseline sensitivities of A. alternata to the new SDHIs fluopyram, fluxapyroxad, and penthiopyrad and assessed their cross resistance patterns with boscalid. Examination of the effective fungicide concentration that inhibits mycelial growth to 50% relative to the control (EC50) for 50 baseline isolates revealed that the majority were sensitive to boscalid, penthiopyrad, fluopyram, and fluxapyroxad. Analysis of EC50 values for boscalid for 117 A. alternata isolates originating from boscalid-exposed orchards showed that 44, 3, 1, and 69 isolates had sensitive, reduced sensitivity, moderately resistant, and highly resistant boscalid phenotypes, respectively. Molecular investigation of the occurrence of known SDH mutations showed that, among the 69 isolates highly resistant to boscalid, 44, 2, 14, and 1 isolates possessed the mutations leading to the H277Y, H277R, H134R, and H133R amino acid substitutions in AaSDHB, AaSDHB, AaSDHC, and AaSDHD subunits, respectively. Some SDHB or SDHC mutants displayed highly sensitive, sensitive, or reduced sensitivity phenotypes toward penthiopyrad or fluxapyroxad, whereas other had low, moderate, or high levels of resistance to these fungicides. In contrast, all the SDHB mutants were sensitive to fluopyram, while 10, 5, and 1 SDHC mutants had sensitive, reduced sensitivity, and moderately resistant fluopyram phenotypes, respectively. The SDHD mutant had reduced sensitivity to fluopyram and penthiopyrad but was highly resistant to fluxapyroxad. The discrepancies of cross-resistance patterns between SDHIs suggest that their binding sites in complex II may differ slightly and that additional mechanisms of resistance to these compounds are likely involved. Ultimately, the findings of this study should lead to the rational and sustained deployment of new SDHIs in Alternaria late blight spray programs.

•While recent studies have elucidated many of the factors driving parasite dynamics during the growing season, the ecological and evolutionary dynamics during the off-season (i.e. the period between growing seasons) remain largely unexplored. •We combine large-scale surveys and detailed experiments to investigate the overwintering success of the specialist plant pathogen Podosphaera plantaginis on its patchily distributed host plant Plantago lanceolata on the Åland Islands. •Twelve years of epidemiological data establish the off-season as a crucial stage in pathogen metapopulation dynamics, with approximately forty percent of the populations going extinct during the off-season. At the end of the growing season, we observed environmentally-mediated variation in the production of resting structures, with major consequences for spring infection at spatial scales ranging from single individuals to populations within a metapopulation. Reciprocal transplant experiments further demonstrated that pathogen population of origin and overwintering site jointly shaped infection intensity in spring, with a weak signal of parasite adaptation to the local off-season environment. •We conclude that environmentally-mediated changes in the distribution and evolution of parasites during the off-season are crucial for our understanding of host-parasite dynamics, with applied implications for combating parasites and diseases in agriculture, wildlife and human disease systems.

International audience; Plant diseases caused by fungi and oomycetes result in significant economic losses every year. Although phylogenetically distant, these organisms share many common features during infection. We identified genes in the oomycete Plasmopara viticola that are potentially involved in pathogenesis in grapevine by using fungal databases and degenerate primers. Fragments of P. viticola genes encoding NADH-ubiquinone oxidoreductase (PvNuo), laccase (PvLac), and invertase (PvInv) were obtained. PvNuo was overexpressed at 2 days postinoculation (dpi), during the development of the first hyphal structures and haustoria. PvLac was overexpressed at 5 dpi when genes related to pterostilbene biosynthesis were induced in grapevine. Transcript level for PvInv increased between 1 and 4 dpi before reaching a plateau. These results might suggest a finely tuned strategy of infection depending on nutrition and plant response. Phylogenetic analyses of PvNuo showed that P. viticola clustered with other oomycetes and was associated with brown algae and diatoms, forming a typical Straminipila clade. Based on the comparison of available sequences for laccases and invertases, the group formed by P. viticola and other oomycetes tended to be more closely related to Opisthokonta than to Straminipila. Convergent evolution or horizontal gene transfer could explain the presence of fungus-like genes in P. viticola.