Relationship Between the Xylem Anatomy of Grapevine Rootstocks and Their Susceptibility to Phaeoacremonium minimum and Phaeomoniella chlamydospora

Health Status of Ready-to-Plant Grapevine Nursery Material in Canada Regarding Young Vine Decline Fungi

Young vine decline (YVD), caused by several taxonomically different fungi, results in the decline and death of grapevines within a few years after planting. Infection can occur in nursery mother blocks and/or at several stages in the nursery propagation process, but the final plant material may remain asymptomatic. Four nurseries that sell ready-to-plant grapevines in Canada were sampled to evaluate the health status with regard to YVD fungi, including Botryosphaeriaceae spp., Cadophora luteo-olivacea, Dactylonectria macrodidyma, Dactylonectria torresensis, Phaeoacremonium minimum, and Phaeomoniella chlamydospora. Plants representing three cultivars, 'Chardonnay', 'Merlot', and 'Pinot noir', either grafted onto '3309C' rootstock or self-rooted, were provided by the nurseries. Samples from the roots, base of the rootstock or self-rooted cultivar, graft-union, and scion were collected from each plant. DNA was extracted, and the total abundance of each fungus was quantified using Droplet Digital PCR. Results revealed that 99% of plants harbored at least one of the fungi studied, with a mean of three different fungal species that were present per grapevine. Droplet Digital PCR results showed that the abundance of the different fungi significantly varied between different sections of each plant, individual plants for each cultivar, and cultivars from the same nursery. Necrosis measurements were recorded from the base of the rootstock or self-rooted cultivars and did not correlate with fungal abundance recorded in that section for each grapevine, but necrosis was consistent across cultivars within nurseries. Five different rootstocks were compared from one nursery, and results showed no differences between rootstocks and their health status. Among all nurseries, C. luteo-olivacea was the most prevalent fungus (97% of the plants), while D. macrodidyma was the least commonly found (13% of the plants). This study shows that ready-to-plant nursery material sold in Canada is likely to be infected with several YVD fungi and that presence and abundance of fungi vary significantly among individual grapevines and nurseries.

Succession of endophytic fungi and rhizosphere soil fungi and their correlation with secondary metabolites in Fagopyrum dibotrys

Golden buckwheat (Fagopyrum dibotrys, also known as F. acutatum) is a traditional edible herbal medicinal plant with a large number of secondary metabolites and is considered to be a source of therapeutic compounds. Different ecological environments have a significant impact on their compound content and medicinal effects. However, little is known about the interactions between soil physicochemical properties, the rhizosphere, endophytic fungal communities, and secondary metabolites in F. dibotrys. In this study, the rhizosphere soil and endophytic fungal communities of F. dibotrys in five different ecological regions in China were identified based on high-throughput sequencing methods. The correlations between soil physicochemical properties, active components (total saponins, total flavonoids, proanthocyanidin, and epicatechin), and endophytic and rhizosphere soil fungi of F. dibotrys were analyzed. The results showed that soil pH, soil N, OM, and P were significantly correlated with the active components of F. dibotrys. Among them, epicatechin, proanthocyanidin, and total saponins were significantly positively correlated with soil pH, while proanthocyanidin content was significantly positively correlated with STN, SAN, and OM in soil, and total flavone content was significantly positively correlated with P in soil. In soil microbes, Mortierella, Trechispora, Exophiala, Ascomycota_unclassified, Auricularia, Plectosphaerella, Mycena, Fungi_unclassified, Agaricomycetes_unclassified, Coprinellus, and Pseudaleuria were significantly related to key secondary metabolites of F. dibotrys. Diaporthe and Meripilaceae_unclassified were significantly related to key secondary metabolites in the rhizome. This study presents a new opportunity to deeply understand soil-plant-fungal symbioses and secondary metabolites in F. dibotrys, as well as provides a scientific basis for using biological fertilization strategies to improve the quality of F. dibotrys.

Secondary metabolites in grapevine: crosstalk of transcriptional, metabolic and hormonal signals controlling stress defence responses in berries and vegetative organs

Abiotic stresses, such as temperature, heat waves, water limitation, solar radiation and the increase in atmospheric CO₂ concentration, significantly influence the accumulation of secondary metabolites in grapevine berries at different developmental stages, and in vegetative organs. Transcriptional reprogramming, miRNAs, epigenetic marks and hormonal crosstalk regulate the secondary metabolism of berries, mainly the accumulation of phenylpropanoids and of volatile organic compounds (VOCs). Currently, the biological mechanisms that control the plastic response of grapevine cultivars to environmental stress or that occur during berry ripening have been extensively studied in many worlds viticultural areas, in different cultivars and in vines grown under various agronomic managements. A novel frontier in the study of these mechanisms is the involvement of miRNAs whose target transcripts encode enzymes of the flavonoid biosynthetic pathway. Some miRNA-mediated regulatory cascades, post-transcriptionally control key MYB transcription factors, showing, for example, a role in influencing the anthocyanin accumulation in response to UV-B light during berry ripening. DNA methylation profiles partially affect the berry transcriptome plasticity of different grapevine cultivars, contributing to the modulation of berry qualitative traits. Numerous hormones (such as abscisic and jasmomic acids, strigolactones, gibberellins, auxins, cytokynins and ethylene) are involved in triggering the vine response to abiotic and biotic stress factors. Through specific signaling cascades, hormones mediate the accumulation of antioxidants that contribute to the quality of the berry and that intervene in the grapevine defense processes, highlighting that the grapevine response to stressors can be similar in different grapevine organs. The expression of genes responsible for hormone biosynthesis is largely modulated by stress conditions, thus resulting in the numeourous interactions between grapevine and the surrounding environment.

Xylem Embolism and Pathogens: Can the Vessel Anatomy of Woody Plants Contribute to X. fastidiosa Resistance?

The maintenance of an intact water column in the xylem lumen several meters above the ground is essential for woody plant viability. In fact, abiotic and biotic factors can lead to the formation of emboli in the xylem, interrupting sap flow and causing consequences on the health status of the plant. Anyway, the tendency of plants to develop emboli depends on the intrinsic features of the xylem, while the cyto-histological structure of the xylem plays a role in resistance to vascular pathogens, as in the case of the pathogenic bacterium Xylella fastidiosa. Analysis of the scientific literature suggests that on grapevine and olive, some xylem features can determine plant tolerance to vascular pathogens. However, the same trend was not reported in citrus, indicating that X. fastidiosa interactions with host plants differ by species. Unfortunately, studies in this area are still limited, with few explaining inter-cultivar insights. Thus, in a global context seriously threatened by X. fastidiosa, a deeper understanding of the relationship between the physical and mechanical characteristics of the xylem and resistance to stresses can be useful for selecting cultivars that may be more resistant to environmental changes, such as drought and vascular pathogens, as a way to preserve agricultural productions and ecosystems.

Minimal versus Intensive: How the Pruning Intensity Affects Occurrence of Grapevine Leaf Stripe Disease, Wood Integrity, and the Mycobiome in Grapevine Trunks

Previous works on grapevine-trunk diseases indicate that minimal or non-pruning of the grapevine under certain circumstances can significantly reduce the risk of symptom expression. Nevertheless, knowledge of the mechanisms behind these observations are limited. Therefore, it was the aim of this study to investigate in more detail the effect of pruning intensity on the grapevine trunk by means of trunk integrity and the fungal community in the wood tissue. Two German vineyards partially trained in vertical-shoot position and semi-minimally pruned hedges were chosen for this survey due to the accessibility of multi-annual esca-monitoring data. The results revealed that only in one of the two vineyards was the incidence of external esca symptoms significantly reduced over a period of five years (2017–2021) by minimal pruning, which was up to 73.7% compared to intensive pruning. In both vineyards, the trunks of intensively pruned vines not only had more pruning wounds on the trunk (by 86.0% and 72.9%, respectively) than minimally pruned vines, but also exhibited a larger (by 19.3% and 14.7%, respectively) circumference of the trunk head. In addition, the percentage of white rot and necrosis in the trunks of esca-positive and esca-negative vines was analyzed and compared between the two pruning intensities; hereby, significant differences were only found for esca-negative ‘Dornfelder’ vines, in which the proportion of necrosis was higher for intensively pruned vines (23.0%) than for minimally pruned vines (11.5%). The fungal communities of the differently pruned vine trunks were mainly dominated by four genera, which are also associated with GTDs: Diplodia, Eutypa, Fomitiporia and Phaeomoniella. All in all, the fungal diversity and community composition did not differ between minimally and intensively pruned, esca-positive vines.