Esca, a Grapevine Trunk Disease (GTD), is of major concern for viticulture worldwide. Our study compares the fungal communities that inhabit the wood tissues of vines that expressed or not foliar esca-symptoms. The trunk and rootstock tissues were apparently healthy, whether the 10 year-old plants were symptomatic or not. The only difference was in the cordon, which contained white rot, a typical form of esca, in 79% of symptomatic plants. Observations over a period of one year using a fingerprint method, Single Strand Conformation Polymorphism (SSCP), and the ITS-DNA sequencing of cultivable fungi, showed that shifts occurred in the fungal communities colonizing the healthy wood tissues. However, whatever the sampling time, spring, summer, autumn or winter, the fungi colonizing the healthy tissues of asymptomatic or symptomatic plants were not significantly different. Forty-eight genera were isolated, with species of Hypocreaceae and Botryosphaeriaceae being the most abundant species. Diverse fungal assemblages, made up of potentially plant-pathogenic and -protective fungi, colonized these non-necrotic tissues. Some fungi, possibly involved in GTD, inhabited the non-necrotic wood of young plants, but no increase in necrosis areas was observed over the one-year period.

The management of certain plant beneficial microorganisms [biological control agents (BCAs)] seems to be a promising and environmental friendly method to control plant pathogens. However, applications are still limited because of the lack of consistency of BCAs when they are applied in the field. In the present paper, the advantages and limitations of BCAs are seen through the example of Pythium oligandrum, an oomycete that has received much attention in the last decade. The biological control exerted by P. oligandrum is the result of a complex process, which includes direct effects through the control of pathogens and/or indirect effects mediated by P. oligandrum, i.e. induction of resistance and growth promotion. P. oligandrum antagonism is a multifaceted and target fungus-dependent process. Interestingly, it does not seem to disrupt microflora biodiversity on the roots. P. oligandrum has an atypical relationship with the plant because it rapidly penetrates into the root tissues but it cannot stay alive in planta. After root colonisation, because of the elicitation by P. oligandrum of the plant-defence system, plants are protected from a range of pathogens. The management of BCAs, here P. oligandrum, is discussed with regard to its interactions with the incredibly complex agrosystems.

A low-molecular weight protein, termed oligandrin, was purified to homogeneity from the culture filtrate of the mycoparasitic fungus Pythium oligandrum. When applied to decapitated tomato (Lycopersicon esculentum Mill. var. Prisca) plants, this protein displayed the ability to induce plant defense reactions that contributed to restrict stem cell invasion by the pathogenic fungus Phytophthora parasitica. According to its N-terminal sequence, low-molecular weight, acidic isoelectric point, ultraviolet spectrum, and migration profile, the P. oligandrum-produced oligandrin was found to share some similarities with several elicitins from other Phytophthora spp. and Pythium spp. However, oligandrin did not induce hypersensitive reactions. A significant decrease in disease incidence was monitored in oligandrin-treated plants as compared with water-treated plants. Ultrastructural investigations of the infected tomato stem tissues from non-treated plants showed a rapid colonization of all tissues associated with a marked host cell disorganization. In stems from oligandrin-treated plants, restriction of fungal growth to the outermost tissues and decrease in pathogen viability were the main features of the host-pathogen interaction. Invading fungal cells were markedly damaged at a time when the cellulose component of their cell walls was quite well preserved. Host reactions included the plugging of intercellular spaces as well as the occasional formation of wall appositions at sites of potential pathogen entry. In addition, pathogen ingress in the epidermis was associated with the deposition of an electron-opaque material in most invaded intercellular spaces. This material, lining the primary walls, usually extended toward the inside to form deposits that frequently interacted with the wall of invading hyphae. In the absence of fungal challenge, host reactions were not detected.

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Pythium oligandrum, a non-pathogenic soil-inhabiting oomycete, colonizes the root ecosystem of many crop species. Whereas most members in the genus Pythium are plant pathogens, P. oligandrum distinguishes itself from the pathogenic species by its ability to protect plants from biotic stresses in addition to promoting plant growth. The success of P. oligandrum at controlling soilborne pathogens is partly associated with direct antagonism mediated by mycoparasitism and antimicrobial compounds. Interestingly, P. oligandrum has evolved with specific mechanisms to attack its prey even when these belong to closely related species. Of particular relevance is the question of how P. oligandrum distinguishes between self-and non-self cell wall degradation during the mycoparasitic process of pathogenic oomycete species. The ability of P. oligandrum to enter and colonize the root system before rapidly degenerating is one of the most striking features that differentiate it from all other known biocontrol fungal agents. In spite of this atypical behaviour, P. oligandrum sensitizes the plant to defend itself through the production of at least two types of microbe-associated molecular patterns, including oligandrin and cell wall protein fractions, which appear to be closely involved in the early events preceding activation of the jasmonic acid-and ethylene-dependent signalling pathways and subsequent localized and systemic induced resistance. The aim of this review is to highlight the expanding knowledge of the mechanisms by which P. oligandrum provides beneficial effects to plants and to explore the potential use of this oomycete or its metabolites as new disease management strategies.

Esca, a major grapevine trunk disease in old grapevines, is associated with the colonization of woody tissues by a broad range of plant pathogenic fungi. To identify which fungal and bacterial species are involved in the onset of this disease, we analysed the microbiota from woody tissues of young (10-yearold) grapevines at an early stage of esca. Using meta-barcoding, 515 fungal and 403 bacterial operational taxonomic units (OTUs) were identified in woody tissues. In situ hybridization showed that these fungi and bacteria co-inhabited in grapevine woody tissues. In non-necrotic woody tissues, fungal and bacterial microbiota varied according to organs and seasons but not diseased plant status. Phaeomoniella chlamydospora, involved in the Grapevine trunk disease, was the most abundant species in non-necrotic tissues from healthy plants, suggesting a possible non-pathogenic endophytic behaviour. Most diseased plants (70%) displayed cordons, with their central white-rot necrosis colonized essentially by two plant pathogenic fungi (Fomitiporia mediterranea: 60%-90% and P. chlamydospora: 5%-15%) and by a few bacterial taxa (Sphingomonas spp. and Mycobacterium spp.). The occurrence of a specific association of fungal and bacterial species in cordons from young grapevines expressing escafoliar symptoms strongly suggests that that microbiota is involved in the onset of this complex disease.

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Background and Aims:The impact of grey mould (Botrytis cinerea (B. cinerea)) was quantified on chemical, phenolic and sensory qualities of grapes, derived musts and wines. Methods and Results: Analyses were carried out by using naturally or artificially infected grape berries at ripeness or overripeness. In grape seeds, chemical analyses revealed no major differences between healthy and rotten grapes. In grape skins of Botrytis-affected berries, concentrations of all the phenolic compounds (anthocyanins and proanthocyanidin monomers, dimers and trimer) decreased drastically. Mean degree of polymerization of the proanthocyanidin polymeric fraction was also affected in skins. Chemical analyses of musts and wines made with different percentages of rotten berries showed a moderate impact of the pathogen on their phenolic composition. Nevertheless, sensory analyses underlined a loss of wine sensory quality perceptible from a threshold as low as 5% of Botrytis-affected grapes onwards. Conclusion: Phenolic variations and the associated negative impact in grapes, derived musts and wines may be related to oxidation phenomena from B. cinerea. The main effects of severity/age of grey mould and the level of berry maturity are also discussed. Significance of the Study: B. cinerea drastically affects the phenolic and organoleptic properties of grape skins and derived wines. Therefore, prophylactic actions early in the vineyard, evaluation of the sanitary status of the harvested grapes and berry sorting are primordial even under low disease pressure.