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Grapevine trunk diseases (GTDs) are progressively affecting vineyard longevity and productivity worldwide. To be able to understand and combat these diseases, we need a different concept of the signals exchanged between the grapevine and fungi than the well-studied pathogen-associated molecular pattern and effector concepts. We screened extracts from fungi associated with GTDs for their association with basal defence responses in suspension cells of grapevine. By activity-guided fractionation of the two selected extracts, O -methylmellein was identified as a candidate modulator of grapevine immunity. O -Methylmellein could not induce immune responses by itself (i.e. does not act as an elicitor), but could amplify some of the defence responses triggered by the bacterial elicitor flg22, such as the induction level of defence genes and actin remodelling. These findings show that Eutypa lata , exemplarily selected as an endophytic fungus linked with GTDs, can secrete compounds that act as amplifiers of basal immunity. Thus, in addition to elicitors that can trigger basal immunity, and effectors that down-modulate antibacterial basal immunity, once it had been activated, E. lata seems to secrete a third type of chemical signal that amplifies basal immunity and may play a role in the context of consortia of mutually competing microorganisms. [ABSTRACT FROM AUTHOR]

Grapevine red blotch-associated virus (GRBaV) is a major threat to the wine industry in the USA. GRBaV infections (aka red blotch disease) compromise crop yield and berry chemical composition, affecting the flavor and aroma properties of must and wine. In this study, we combined genome-wide transcriptional profiling with targeted metabolite analyses and biochemical assays to characterize the impact of the disease on red-skinned berry ripening and metabolism. Using naturally infected berries collected from two vineyards, we were able to identify consistent berry responses to GRBaV across different environmental and cultural conditions. Specific alterations of both primary and secondary metabolism occurred in GRBaV-infected berries during ripening. Notably, GRBaV infections of post-véraison berries resulted in the induction of primary metabolic pathways normally associated with early berry development (e.g. thylakoid electron transfer and the Calvin cycle), while inhibiting ripening-associated pathways, such as a reduced metabolic flux in the central and peripheral phenylpropanoid pathways. We show that this metabolic reprogramming correlates with perturbations at multiple regulatory levels of berry development. Red blotch caused the abnormal expression of transcription factors (e.g. NACs, MYBs, and AP2-ERFs) and elements of the post-transcriptional machinery that function during red-skinned berry ripening. Abscisic acid, ethylene, and auxin pathways, which control both the initiation of ripening and stress responses, were also compromised. We conclude that GRBaV infections disrupt normal berry development and stress responses by altering transcription factors and hormone networks, which result in the inhibition of ripening pathways involved in the generation of color, flavor, and aroma compounds. [ABSTRACT FROM AUTHOR]

A major aim in grapevine breeding is the provision of cultivars resistant to downy mildew. As Plasmopara viticola produces sporangia on the abaxial surface of susceptible cultivars, disease symptoms on both leaf sides may be detected and quantified by technical sensors. The response of cultivars 'Mueller-Thurgau', 'Regent', and 'Solaris', which differ in resistance to P. viticola, was characterized under controlled conditions by using hyperspectral sensors. Spectral reflectance was suitable to differentiate between non-infected cultivars and leaf sides of the bicolored grapevine. Brown discoloration of tissue became visible on both leaf sides of resistant cultivars 2 days before downy mildew symptoms appeared on the susceptible 'Mueller-Thurgau' cultivar. Infection of this cultivar resulted in significant (P<0.05) reflectance changes 1-2 days prior to abaxial sporulation induced by high relative humidity, or the formation of adaxial oil spots. Hyperspectral imaging was more sensitive in disease detection than non-imaging and provided spatial information on the leaf level. Spectral indices provided information on the variability of chlorophyll content, photosynthetic activity, and relative water content of leaf tissue in time and space. On 'Mueller-Thurgau' downy mildew translated reflectance to higher values as detectable by the index DMI_3=(R470+R682+R800)/(R800/R682) and affected reflectance at 1450 nm. Tissue discoloration on 'Regent' and 'Solaris' cultivars was associated with lower reflectance between 750 and 900 nm; blue and red reflectance demonstrated differences from leaf necroses. With high inoculum densities, P. viticola sporulated on even resistant cultivars. Hyperspectral characterization at the tissue level proved suitable for phenotyping plant resistance to pathogens and provided information on resistance mechanisms. [ABSTRACT FROM AUTHOR]

A 15-day survey of autofluorescence has been conducted upon infection by downy mildew [Plasmopara viticola (Berk. & M.A. Curtis) Berl. & de Toni] of leaves of a susceptible grapevine genotype. Different autofluorescence signals were followed from the cellular to the whole-leaf level by using four types of devices for fluorosensing: a macroscope, a spectrofluorimeter, a portable field optical sensor (the Multiplex 3), and a field fluorescence sensor prototype with 335nm excitation. It was shown for the first time, by the three different techniques and at three different scales, that the stilbene-dependent violet–blue autofluorescence (VBF) had a transitory behaviour, increasing to a maximum 6 days post-inoculation (DPI) and then decreasing to a constant lower level, nevertheless significantly higher than in the control leaf. This behaviour could be sensed from both sides of the leaf. On the abaxial side, VBF could discriminate the presence of infection from 1 DPI, and on the adaxial side from 3 DPI. There was a constant increase in blue-excited green fluorescence starting from 8 DPI, concomitant with a decrease in leaf chlorophyll content sensed by one reflectance and two fluorescence indices available on the Multiplex 3 sensor. These results show that a pre-symptomatic and symptomatic sensing of downy mildew is possible by autofluorescence-based sensors, and this is potentially applicable in the field. [ABSTRACT FROM AUTHOR]

The ectoparasitic dagger nematode (Xiphinema index), vector of Grapevine fanleaf virus (GFLV), provokes gall formation and can cause severe damage to the root system of grapevines. Mycorrhiza formation by Glomus (syn. Rhizophagus) intraradices BEG141 reduced both gall formation on roots of the grapevine rootstock SO4 (Vitis berlandieri×V. riparia) and nematode number in the surrounding soil. Suppressive effects increased with time and were greater when the nematode was post-inoculated rather than co-inoculated with the arbuscular mycorrhizal (AM) fungus. Using a split-root system, decreased X. index development was shown in mycorrhizal and non-mycorrhizal parts of mycorrhizal root systems, indicating that both local and systemic induced bioprotection mechanisms were active against the ectoparasitic nematode. Expression analyses of ESTs (expressed sequence tags) generated in an SSH (subtractive suppressive hybridization) library, representing plant genes up-regulated during mycorrhiza-induced control of X. index, and of described grapevine defence genes showed activation of chitinase 1b, pathogenesis-related 10, glutathione S-transferase, stilbene synthase 1, 5-enolpyruvyl shikimate-3-phosphate synthase, and a heat shock proein 70-interacting protein in association with the observed local and/or systemic induced bioprotection against the nematode. Overall, the data suggest priming of grapevine defence responses by the AM fungus and transmission of a plant-mediated signal to non-mycorrhizal tissues. Grapevine gene responses during AM-induced local and systemic bioprotection against X. index point to biological processes that are related either to direct effects on the nematode or to protection against nematode-imposed stress to maintain root tissue integrity. [ABSTRACT FROM PUBLISHER]