Comparison of the Molecular Responses of Tolerant, Susceptible and Highly Susceptible Grapevine Cultivars During Interaction With the Pathogenic Fungus Eutypa lata

Two Paenibacillus spp. strains promote grapevine wood degradation by the fungus Fomitiporia mediterranea: from degradation experiments to genome analyses

Ascomycetes, basidiomycetes and deuteromycetes can degrade wood, but less attention has been paid to basidiomycetes involved in Esca, a major Grapevine Trunk Disease. Using a wood sawdust microcosm system, we compared the wood degradation of three grapevine cultivars inoculated with Fomitiporia mediterranea M. Fisch, a basidiomycete responsible for white-rot development and involved in Esca disease. The grapevine cultivar Ugni blanc was more susceptible to wood degradation caused by F. mediterranea than the cultivars Cabernet Sauvignon and Merlot. Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy showed that F. mediterranea preferentially degrades lignin and hemicellulose over cellulose (preferential, successive or sequential white-rot). In addition, co-inoculation of sawdust with two cellulolytic and xylanolytic bacterial strains of Paenibacillus (Nakamura) Ash (Paenibacillus sp. (S231-2) and P. amylolyticus (S293)), enhanced F. mediterranea ability to degrade Ugni blanc. The NMR data further showed that the increase in Ugni blanc sawdust degradation products was greater when bacteria and fungi were inoculated together. We also demonstrated that these two bacterial strains could degrade the wood components of Ugni blanc sawdust. Genome analysis of these bacterial strains revealed numerous genes predicted to be involved in cellulose, hemicellulose, and lignin degradation, as well as several other genes related to bacteria-fungi interactions and endophytism inside the plant. The occurrence of this type of bacteria-fungus interaction could explain, at least in part, why necrosis develops extensively in certain grapevine varieties such as Ugni blanc.

Hybrid Vitis Cultivars with American or Asian Ancestries Show Higher Tolerance towards Grapevine Trunk Diseases

Grape production worldwide is increasingly threatened by grapevine trunk diseases (GTDs). No grapevine cultivar is known to be entirely resistant to GTDs, but susceptibility varies greatly. To quantify these differences, four Hungarian grape germplasm collections containing 305 different cultivars were surveyed to determine the ratios of GTDs based on symptom expression and the proportion of plant loss within all GTD symptoms. The cultivars of monophyletic Vitis vinifera L. origin were amongst the most sensitive ones, and their sensitivity was significantly (p < 0.01) higher than that of the interspecific (hybrid) cultivars assessed, which are defined by the presence of Vitis species other than V. vinifera (e.g., V. labrusca L., V. rupestris Scheele, and V. amurensis Rupr.) in their pedigree. We conclude that the ancestral diversity of grapes confers a higher degree of resilience against GTDs.

A Panoramic View on Grapevine Trunk Diseases Threats: Case of Eutypa Dieback, Botryosphaeria Dieback, and Esca Disease

Grapevine trunk diseases (GTD) are currently one of the most devastating and challenging diseases in viticulture, leading to considerable yield losses and a remarkable decline in grapevine quality. The identification of the causal agents is the cornerstone of an efficient approach to fighting against fungal diseases in a sustainable, non-chemical manner. This review attempts to describe and expose the symptoms of each pathology related to GTD, the modes of transmission, and the harmfulness of recently reported agents. Special attention was given to new diagnostic tests and technologies, grapevine defense mechanisms, molecular mechanisms of endophytes fungal colonization, and management strategies used to control these threats. The present extended review is, therefore, an updated state-of-the-art report on the progress in the management of vineyards.

Metagenomic Assessment Unravels Fungal Microbiota Associated to Grapevine Trunk Diseases

Grapevine trunk diseases (GTDs) are among the most important problems that affect the longevity and productivity of vineyards in all the major growing regions of the world. They are slow-progression diseases caused by several wood-inhabiting fungi with similar life cycles and epidemiology. The simultaneous presence of multiple trunk pathogens in a single plant together with the inconsistent GTDs symptoms expression, their isolation in asymptomatic plants, and the absence of effective treatments make these diseases extremely complex to identify and eradicate. Aiming to gain a better knowledge of GTDs and search sustainable alternatives to limit their development, the present work studied the fungal community structure associated with GTDs symptomatic and asymptomatic grapevines, following a metagenomic approach. Two important cultivars from the Alentejo region with different levels of susceptibility to GTDs were selected, namely, ‘Alicante Bouschet’ and ‘Trincadeira’. Deep sequencing of fungal-directed ITS1 amplicon led to the detection of 258 taxa, including 10 fungi previously described as responsible for GTDs. Symptomatic plants exhibited a lower abundance of GTDs-associated fungi, although with significantly higher diversity of those pathogens. Our results demonstrated that trunk diseases symptoms are intensified by a set of multiple GTDs-associated fungi on the same plant. The composition of fungal endophytic communities was significantly different according to the symptomatology and it was not affected by the cultivar. This study opens new perspectives in the study of GTDs-associated fungi and their relation to the symptomatology in grapevines.

Elucidation of the molecular responses during the primary infection of wild blueberry phenotypes with Monilinia vaccinii-corymbosi under field conditions

BACKGROUND

Monilinia blight caused by Monilinia vaccinii-corymbosi (Reade) Honey (M.vc) is a major disease of wild blueberry that can result in severe crop losses in the absence of an integrated disease management programme. The fungus causes blight in the emerging floral and vegetative buds, but the degree of susceptibility varies among the different wild blueberry phenotypes, ranging from the highly susceptible V. a. f. nigrum to the moderately susceptible V. angustifolium and the least susceptible V. myrtilloides.

RESULTS

The present study evaluated the defense responses of these major phenotypes during their primary infection (floral buds) with M.vc. The temporal expression profiles of PR genes (PR3 and PR4) and the flavonoid pathway structural genes (CHS, ANS, ANR, DFR and FLS) were analysed. The PR3 and PR4 gene expression profiles revealed that V. myrtilloides responded to M.vc infection by activating the expression of both PR genes. V. a. f. nigrum, on the other hand, failed to activate these genes, while V. angustifolium, exhibited an intermediate response. Our study with the flavonoid pathway genes indicated variability in activation of the genes during post-infection time points with ANS and ANR in V. myrtilloides, FLS in V. angustifolium and no response observed in V. a. f. nigrum.

CONCLUSIONS

Altogether, this study highlights that the degree of phenotype susceptibility is associated with the timely activation of host defense responsive genes. Data obtained in this study provided a starting point for a better understanding of the wild blueberry- M. vaccinii-corymbosi pathosystem.

Endophytic Fungi as Potential Biological Control Agents against Grapevine Trunk Diseases in Alentejo Region

Simple Summary

Grapevine trunk diseases are the most widespread fungal diseases, affecting grapevines in all the major growing regions of the world, and their complete eradication is still not possible. Aiming to search alternatives to avoid the spread and high incidence of these diseases, the present work identified in vineyards within the Alentejo region the grapevine fungal community and among it the fungi responsible for those diseases. Grapevine fungal community showed a wide variety of fungi, nine of them previously described as grapevine trunk diseases-associated fungi. Almost all these fungi were detected in symptomatic and asymptomatic plants, which shows the importance of investigating the interactions of fungal communities and confirms the need for early diagnosis of these diseases. The potential of endophytic fungi as bio-control agents was tested against grapevine trunk diseases-associated fungi. These tests were performed among identified endophytes and grapevine trunk diseases phytopathogenic fungi, and all the endophyte fungi showed potential as biocontrol agents. Our findings suggest that endophytes are promising candidates for their use in biological control due to their antagonistic activity against the mycelia growth of grapevine trunk diseases-associated fungi.

Abstract

Grapevine trunk diseases (GTDs) are the most widespread fungal diseases, affecting grapevines in all the major growing regions of the world, and their complete eradication is still not possible. Aiming to search alternatives to avoid the spread and high incidence of these diseases, the present work intended to molecularly identify the grapevine endophytic community, the phytopathogenic fungi associated with GTDs in vineyards within the Alentejo region, and to test potential antagonist microorganisms as biological control candidates against GTDs-associated fungi. Grapevine endophytic community showed a wide variety of fungi in GTDs’ asymptomatic and symptomatic plants, nine of them previously described as GTDs-associated fungi. GTDs prevalent fungi identified in symptomatic plants were Diaporthe sp., Neofusicoccum sp., and H. viticola. Almost all these fungi were also detected in asymptomatic plants, which shows the importance of investigating the interactions of fungal communities and confirms the need for early diagnosis of these diseases. Direct inhibition antagonism tests were performed among identified endophytes and GTDs phytopathogenic fungi, and all the endophyte fungi showed potential as biocontrol agents. Our findings suggest that endophytes are promising candidates for their use in biological control due to their antagonistic activity against the mycelia growth of some GTDs-associated fungi.

Behind the curtain of the compartmentalization process: Exploring how xylem vessel diameter impacts vascular pathogen resistance

A key determinant of plant resistance to vascular infections lies in the ability of the host to successfully compartmentalize invaders at the xylem level. Growing evidence supports that the structural properties of the vascular system impact host vulnerability towards vascular pathogens. The aim of this study was to provide further insight into the impact of xylem vessel diameter on compartmentalization efficiency and thus vascular pathogen movement, using the interaction between Vitis and Phaeomoniella chlamydospora as a model system. We showed experimentally that an increased number of xylem vessels above 100 μm of diameter resulted in a higher mean infection level of host tissue. This benchmark was validated within and across Vitis genotypes. Although the ability of genotypes to restore vascular cambium integrity upon infection was highly variable, this trait did not correlate with their ability to impede pathogen movement at the xylem level. The distribution of infection severity of cuttings across the range of genotype's susceptibility suggests that a risk-based mechanism is involved. We used this experimental data to calibrate a mechanistic stochastic model of the pathogen spread and we provide evidence that the efficiency of the compartmentalization process within a given xylem vessel is a function of its diameter.

Selection and validation of reliable reference genes for gene expression studies from Monilinia vaccinii-corymbosi infected wild blueberry phenotypes

Monilinia blight disease caused by Monilinia vaccinii-corymbosi (Reade) Honey (M.vc) causes severe damage and economic losses in wild blueberry growing regions. Molecular mechanisms regulating defence responses of wild blueberry phenotypes towards this causal fungus are not yet fully known. A reliable quantification of gene expression using quantitative real time PCR (qPCR) is fundamental for measuring changes in target gene expression. A crucial aspect of accurate normalisation is the choice of appropriate reference genes. This study evaluated the expression stability of seven candidate reference genes (GAPDH, UBC9, UBC28, TIP41, CaCSa, PPR and RH8) in floral tissues of diploid and tetraploid wild blueberry phenotypes challenged with M.vc. The expression stability was calculated using five algorithms: geNorm, NormFinder, BestKeeper, deltaCt and RefFinder. The results indicated that UBC9 and GAPDH were the most stable reference genes, while RH8 and PPR were the least stable ones. To further validate the suitability of the analyzed reference genes, the expression level of a pathogenesis related protein gene (i.e., PR3) was analysed for both phenotypes at four time points of infection. Our results may be beneficial for future studies involving the quantification of relative gene expression levels in wild blueberry species.

Wood Metabolomic Responses of Wild and Cultivated Grapevine to Infection with Neofusicoccum parvum, a Trunk Disease Pathogen

Grapevine trunk diseases (GTDs), which are associated with complex of xylem-inhabiting fungi, represent one of the major threats to vineyard sustainability currently. Botryosphaeria dieback, one of the major GTDs, is associated with wood colonization by Botryosphaeriaceae fungi, especially Neofusicoccum parvum. We used GC-MS and HPLC-MS to compare the wood metabolomic responses of the susceptible Vitis vinifera subsp. vinifera (V. v. subsp. vinifera) and the tolerant Vitis vinifera subsp. sylvestris (V. v. subsp. sylvestris) after artificial inoculation with Neofusicoccum parvum (N. parvum). N. parvum inoculation triggered major changes in both primary and specialized metabolites in the wood. In both subspecies, infection resulted in a strong decrease in sugars (fructose, glucose, sucrose), whereas sugar alcohol content (mannitol and arabitol) was enhanced. Concerning amino acids, N. parvum early infection triggered a decrease in aspartic acid, serine, and asparagine, and a strong increase in alanine and β-alanine. A trend for more intense primary metabolism alteration was observed in V. v. subsp. sylvestris compared to V. v. subsp. vinifera. N. parvum infection also triggered major changes in stilbene and flavonoid compounds. The content in resveratrol and several resveratrol oligomers increased in the wood of both subspecies after infection. Interestingly, we found a higher induction of resveratrol oligomer (putative E-miyabenol C, vitisin C, hopeaphenol, ampelopsin C) contents after wood inoculation in V. v. subsp. sylvestris.