The Role of Low Molecular Weight Fungal Metabolites in Grapevine Trunk Disease Pathogenesis: Eutypa Dieback and Esca

Eutypa dieback and Esca are serious grapevine trunk diseases (GTDs) caused by fungal consortia causing large economic losses in vineyards. Depending on the disease the species involved include Eutypa lata, Phaeoacremonium minimum, and Phaeomoniella chlamydospora. There is a need to understand the complex pathogenesis mechanisms used by these fungi to develop treatments for the diseases they cause. Low molecular weight metabolites (LMW) are known to be involved in non-enzymatic oxygen radical generation in fungal degradation of wood by some Basidiomycota species, and as part of our work to explore the basis for fungal consortia pathogenesis, LMW metabolite involvement by the causal GTD fungi was explored. The GTD fungal pathogens examined, E. lata, P. minimum and P. chlamydospora, were found to produce low molecular weight iron binding metabolites that preferentially reduced iron or redox cycled to produce hydrogen peroxide. Uniquely, different LMW metabolites isolated from the GTD fungi promoted distinct chemistries that are important in a type of non-enzymatic catalysis known as chelator-mediated Fenton (CMF) reactions. CMF chemistry promoted by LMW metabolites from these fungi allowed for the generation of highly reactive hydroxyl radicals under conditions promoted by the fungi. We hypothesize that this new reported mechanism may help to explain the necrosis of woody grapevine tissue as a causal mechanism important in pathogenesis in these two grapevine trunk diseases.

Assessment of canopy size using UAV-based point cloud analysis to detect the severity and spatial distribution of canopy decline

This study aimed to validate the use of UAV-based point cloud analysis to detect canopy decline severity and its spatial distribution in vineyards.A new approach to assess canopy decline, caused by Eutypa dieback-like symptoms, using unmanned aerial vehicle (UAV) remote sensing was compared with ground visual assessment in the vineyard. Canopy point cloud captured by UAV-based imagery during the growing season was analysed by a customized program to determine canopy decline severity and spatial distribution in a symptomatic Shiraz vineyard in Eden Valley, South Australia. Experienced assessors performed a ground visual assessment in the vineyard at E-L stage 15. k-means clustering was used to detect reduced canopy volume due to Eutypa dieback-like symptoms. Results from point cloud analysis showed that 12.5 % of the total canopy length in the vineyard had Eutypa dieback symptoms while the ground visual assessment detected 11.4 %. Confusion matrix results showed an accuracy of 87.4 % and a kappa coefficient of 0.43 compared with ground visual assessments. Additionally, automatic analysis of the point cloud was quicker than the ground visual assessment and generated precise geographic coordinates of the symptomatic canopy sections. Point cloud analysis can detect Eutypa dieback-like symptoms and its spatial distribution with 87.4 % accuracy, compared with the ground assessment. Similar to ground visual assessment, E-L stage 15 appears to be a suitable stage to apply point cloud analysis to make Eutypa dieback-like symptom assessments. Grapevine canopy decline, caused by various factors such as Eutypa dieback and inadequate management, can cause yield reduction and threaten vineyard longevity. Compared with tedious ground visual assessments, point cloud analysis can accelerate the assessment of canopy decline in vineyards and help with the planning of remedial practices using precise geographic coordinates of the affected sections.

In vitro evaluation of grapevine endophytes, epiphytes and sap micro-organisms for potential use to control grapevine trunk disease pathogens

SummaryGrapevine trunk diseases (GTDs) threaten the economic sustainability of viticulture worldwide causing a significant reduction of both yields and quality of grapes. Biological control presents a promising sustainable alternative to cultural and chemical methods to mitigate the effects of pathogens causing GTDs, including Botryosphaeria dieback, Eutypa dieback and Esca. This study aimed to identify naturally occurring potential biological control agents from a variety of grapevine tissues, including sap, cane and pith and evaluate their antagonistic activity against selected fungal pathogens responsible for GTDs in vitro. Bacterial and fungal isolates were preliminary screened in vitro to determine their antifungal activity via a dual culture assay against Neofusicoccum parvum and Eutypa lata. Among the fungal isolates, Trichoderma spp. inhibited E. lata mycelial growth up to 64% and N. parvum mycelial growth up to 73% with overgrowth and stopped growth being the likely antagonistic mechanisms. Among the bacterial isolates, Bacillus spp. inhibited E. lata mycelial growth up to 20% and N. parvum mycelial growth up to 40%. Select antagonistic isolates of Trichoderma, Bacillus and Aureobasidium spp. were subject to further dual culture antifungal analysis against Diplodia seriata and Diaporthe ampelina, with Trichoderma isolates consistently causing the greatest inhibition. Volatile organic compound antifungal analysis revealed that these Trichoderma isolates resulted significantly inhibited mycelial growth of N. parvum, E. lata and D. ampelina causing up to 20.11%, 60.55% and 70.9% inhibition respectively (P≤0.05). Multilocus sequence analysis revealed that the Trichoderma isolates are most closely related to Trichoderma asperellum and Trichoderma hamatum. This study identifies grapevine sap as a novel source of potential biological control agents for control of GTDs to support existing efforts to control GTDs. Further testing will be necessary to fully characterize these microbes mode of antagonism and assess their efficacy for pruning wound protection in planta.

Grapevine Trunk Diseases Management in Vineyards from Central Transylvania

Grapevine trunk diseases (GTD) are among the most important diseases reported in vineyards in central Transylvania. On average, up to 5% of the vineyards are affected by the GTD although there are also vineyards where the incidence of the attack exceeds 15%. Recent studies show that the importance of pathogens in wood is so great that they are considered limiting factors that affect the stability of the world’s vineyards. The main objective of this study is to develop new sustainable management alternatives for the GTD control. For this purpose, an agroecological variant including prophylactic and cultural measures and two treatments with biofungicides based on: Trichoderma atroviride strain 8, Trichoderma atroviride strain B11 and Trichoderma harzianum, were tested. The frequency of the attack of the main four GTD diseases (Esca complex, Phomopsis dieback, Eutypa dieback and Crown gall) on the SCDVV Blaj homologated grapevine varieties, ‘Astra’, ‘Amurg’, ‘Brumariu’, ‘Blasius’ ‘Radames’, ‘Rubin’ and ‘Selena’, was assessed showing that these had a lower frequency of the symptoms compared with the widely cultivated variety ‘Feteasca regala’. Also the effect of training system (Classical versus semi-high Guyot) on GTD is presented. The classical system had decreased the frequency of crown gall and Phomopsis dieback, and the semi-high Guyot system had decreased Eutypa dieback’s frequency, indicating that the training system is an important tool of the agroecological system in maintaing the health of grapevine. Biofungicides tested help reduce the symptoms of GTD, but not enough to help reduce the premature death of grapevine.

Eutypa, Eutypella, and Cryptovalsa Species (Diatrypaceae) Associated with Prunus Species in South Africa

Stone fruit trees (Prunus spp.) are economically important fruit trees cultivated in South Africa. These trees are often grown in close proximity to vineyards and are to a large extent affected by the same trunk disease pathogens as grapevines. The aim of the present study was to determine whether stone fruit trees are inhabited by Diatrypaceae species known from grapevines and whether these trees could act as alternative hosts for these fungal species. Isolations were carried out from symptomatic wood of Prunus species (almond, apricot, cherry, nectarine, peach, and plum) in stone fruit growing areas in South Africa. Identification of isolates was based on phylogenetic analyses of the internal transcribed spacer region and β-tubulin gene. Forty-six Diatrypaceae isolates were obtained from a total of 380 wood samples, from which five species were identified. All five species have also been associated with dieback of grapevine. The highest number of isolates was found on apricot followed by plum. No Diatrypaceae species were isolated from peach and nectarine. Eutypa lata was the dominant species isolated (26 isolates), followed by Cryptovalsa ampelina (7), Eutypa cremea (5), Eutypella citricola (5), and Eutypella microtheca (3). First reports from Prunus spp. are E. cremea, E. citricola, and E. microtheca. Pathogenicity tests conducted on apricot and plum revealed that all these species are pathogenic to these hosts, causing red-brown necrotic lesions like those typical of Eutypa dieback on apricot.

Grapevine Trunk Diseases: A Review of Fifteen Years of Trials for Their Control with Chemicals and Biocontrol Agents

Grapevine trunk diseases (GTDs) represent one of the most important problems for viticulture worldwide. Beyond the original causes of this outbreak in some countries like France, the lack of efficient control protocols and the prohibition of using active ingredients such as sodium arsenite and benzimidazoles, until recently used to reduce the impact of some GTDs but deleterious for humans and the environment, have probably worsened the impact of the diseases, leading to increasing economic losses. Since 1990, searches have been made to find efficient tools to control GTDs, testing a wide range of active ingredients and biocontrol agents. This review provides readers with an overview of the results reported in the scientific literature over the last 15 years. In particular, the review focuses on the trials carried out applying chemicals or microorganisms to control Esca complex diseases, Botryosphaeria dieback, and Eutypa dieback, the most widespread GTDs.

Preventative Disease Management and Grower Decision Making: A Case Study of California Wine-Grape Growers

Preventative disease management is challenging to farmers because it requires paying immediate costs in the hopes of returning uncertain future benefits. Understanding farmer decision making about prevention has the potential to reduce disease incidence and minimize the need for more costly postinfection practices. For example, the grapevine trunk-disease complex (esca, Botryosphaeria dieback, Eutypa dieback, and Phomopsis dieback) significantly affects vineyard productivity and longevity. Given the chronic nature of the infections and inability to eradicate the fungal pathogens, the preventative practices of delayed pruning, applications of pruning-wound protectants, and double pruning (also known as prepruning) are the most effective means of management. We surveyed wine-grape growers in six regions of California on their use of these three practices. In spite of acknowledging the yield impacts of trunk diseases, a substantial number of respondents either choose not to use preventative practices or incorrectly adopted them in mature vineyards, too late in the disease cycle to be effective. Growers with more negative perceptions of cost efficacy were less likely to adopt preventative practices or were more likely to time adoption incorrectly in mature vineyards. In general, preventative management may require strong intervention in the form of policy or extension to motivate behavioral change.

The Role of Pest Control Advisers in Preventative Management of Grapevine Trunk Diseases

Vineyards with trunk diseases (Botryosphaeria dieback, Esca, Eutypa dieback, and Phomopsis dieback) can have negative returns in the long run. Minimizing economic impacts depends on effective management, but adopting a preventative practice after infection occurs may not improve yields. Pest control advisers may reduce grower uncertainty about the efficacy of and need for prevention, which often entails future and unobservable benefits. Here, we surveyed advisers in California to examine their influence over grower decision-making, in the context of trunk diseases, which significantly limit grape production and for which curative practices are unavailable. Our online survey revealed adviser awareness of high disease incidence, and reduced yields and vineyard lifespan. Advisers rated both preventative and postinfection practices positively. Despite higher cost estimates given to postinfection practices, advisers did not recommend preventative practices at higher rates. High recommendation rates were instead correlated with high disease incidence for both preventative and postinfection practices. Recommendation rates declined with increasing cost for preventative, but not for postinfection, practices. Our findings suggest that even when advisers acknowledge the risks of trunk diseases, they may not recommend preventative practices before infection occurs. This underscores the importance of clear outreach, emphasizing both the need for prevention and its long-term cost efficacy.