Grapevine Trunk Disease Pathogens Research Articles

Dissemination of esca-related pathogens in German vineyards: do arthropods play roles in vectoring spores?

Grapevine Trunk Diseases (GTDs) such as esca challenge viticulture. The main fungal agents of Petri disease or young esca, Phaeomoniella chlamydospora (Pch), diverse Phaeoacremonium species (Pm spp.) and Cadophora luteo-olivacea (Clo), are transmitted to pruning wounds of vines by rain splashes and air currents. Arthropod-mediated dispersal is another possibility for the pathogens to reach pruning wounds. The present study was the first to evaluate possible involvement of arthropods in the dissemination process of esca-related pathogens in German vineyards. Diversity of arthropods on grapevine trunks was determined in 2019 and 2020, using cardboard traps mounted on vine trunks. Captured arthropods were surveyed for the presence of esca-related pathogens on their exoskeletons by using a nested multiplex PCR. In total, 2099 arthropods were examined, of which 35% were positive for Phaeomoniella chlamydospora (Pch), 21% for Phaeoacremonium spp. (Pm), and 7% for Cadophora luteo-olivacea (Clo). Earwigs and spiders were the most prevalent trapped arthropods; Pch was detected on 27% of earwigs and 38% of spiders, Pm spp. on 17 and 19%, and Clo on 3 and 8% of these arthropods. In both years, arthropods carrying the pathogens were already present in April, and therefore within the presumed susceptibility phase of pruned vines. These results indicate involvement of arthropods in the dispersal of esca-related pathogens in German vineyards. Further research, particularly to determine the infection potential of insect-borne fungi, is needed to confirm transmission risk. These results underline the importance of protecting vine pruning wounds to prevent host invasion by GTD pathogens.

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

Grapevine trunk diseases (GTDs) threaten the economic sustainability of viticulture, causing reductions of yield and quality of grapes. Biological control is 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 grapevine sap, cane and pith tissues, and evaluate their in vitro antagonistic activity against selected fungal GTD pathogens. Bacterial and fungal isolates were preliminarily screened in dual culture assays to determine their antifungal activity against Neofusicoccum parvum and Eutypa lata. Among the fungal isolates, Trichoderma spp. inhibited mycelium growth of E. lata by up to 64% and of N. parvum by up to 73%, with overgrowth and growth cessation being the likely antagonistic mechanisms. Among the bacterial isolates, Bacillus spp. inhibited mycelium growth of E. lata by up to 20% and of N. parvum by up to 40%. Selected antagonistic isolates of Trichoderma, Bacillus and Aureobasidium spp. were subjected to further dual culture antifungal analyses against Diplodia seriata and Diaporthe ampelina, with Trichoderma isolates consistently causing the greatest inhibition. Volatile organic compound antifungal analyses showed that these Trichoderma isolates inhibited mycelium growth of N. parvum (20% inhibition), E. lata (61% inhibition) and Dia. ampelina (71% inhibition). Multilocus sequence analyses revealed that the Trichoderma isolates were most closely related to Trichoderma asperellum and Trichoderma hamatum. This study had identified grapevine sap as a novel source of potential biological control agents for control of GTDs. Further testing will be necessary to fully characterize modes of antagonism of these microorganisms, and assess their efficacy for pruning wound protection in planta.

DNA-based detection of grapevine trunk-disease pathogens from environmental spore samples

In California vineyards, spore dispersal of fungi that cause grapevine trunk diseases Botryosphaeria dieback and Eutypa dieback occurs with winter rains. Spores infect through pruning wounds made to the woody structure of the vine in winter. Better timing of preventative practices that minimize infection may benefit from routine spore-trapping, which could pinpoint site-specific time frames of spore dispersal. To speed pathogen detection from environmental spore samples, we identified species-specific PCR primers and protocols. Then we compared the traditional culture-based method versus our new DNA-based method.•PCR primers for Botryosphaeria-dieback pathogen Neofusicoccum parvum and Eutypa-dieback pathogen Eutypa lata were confirmed species-specific, through extensive testing of related species (in families Botryosphaeriaceae and Diatrypaceae, respectively), other trunk-disease pathogens, and saprophytic fungi that sporulate in vineyards.•Consistent detection of N. parvum was achieved from spore suspensions used fresh or stored at -20°C, whereas consistent detection of E. lata was achieved only with a new spore-lysis method, using zirconia/silica beads in a FastPrep homogenizer (MP Biomedicals; Solon, Ohio, USA), and only from spore suspensions used fresh. Freezing E. lata spores at -20°C made detection inconsistent.•From environmental samples, spores of E. lata were detected only via PCR, whereas spores of N. parvum were detected both via PCR and in culture.

Diversity Profiling of Grapevine Microbial Endosphere and Antagonistic Potential of Endophytic Pseudomonas Against Grapevine Trunk Diseases.

Grapevine trunk diseases (GTDs) are a serious problem of grapevines worldwide. The microbiota of the grapevine endosphere comprises prokaryotic and eukaryotic endophytes, which may form varied relationships with the host plant from symbiotic to pathogenic. To explore the interaction between grapevine endophytic bacteria and GTDs, the endomicrobiome associated with grapevine wood was characterized using next-generation Illumina sequencing. Wood samples were collected from grapevine trunks with and without external symptoms of GTD (cankers) from two vineyards in the Hunter Valley and Hilltops, NSW, Australia and metagenomic characterization of the endophytic community was conducted using the 16S rRNA gene (341F/806R) and ITS (1F/2R) sequences. Among the important GTD pathogens, Phaeomoniella, Phaeoacremonium, Diplodia and Cryptovalsa species were found to be abundant in both symptomatic and asymptomatic grapevines from both vineyards. Eutypa lata and Neofusicoccum parvum, two important GTD pathogens, were detected in low numbers in Hilltops and the Hunter Valley, respectively. Interestingly, Pseudomonas dominated the bacterial community in canker-free grapevine tissues in both locations, comprising 56–74% of the total bacterial population. In contrast, the Pseudomonas population in grapevines with cankers was significantly lower, representing 29 and 2% of the bacterial community in Hilltops and the Hunter Valley, respectively. The presence of Pseudomonas in healthy grapevine tissues indicates its ability to colonize and survive in the grapevine. The potential of Pseudomonas spp. as biocontrol agents against GTD pathogens was also explored. Dual culture tests with isolated fluorescent Pseudomonas against mycelial discs of nine Botryosphaeria dieback, three Eutypa dieback, and two Esca/Petri disease pathogens, revealed antagonistic activity for 10 Pseudomonas strains. These results suggest the potential of Pseudomonas species from grapevine wood to be used as biocontrol agents to manage certain GTD pathogens.

Grapevine trunk diseases in German viticulture. III. Biodiversity and spatial distribution of fungal pathogens in rootstock mother plants and possible relation to leaf symptoms

Three rootstock mother blocks, planted with cultivars SO4 (planted 2004), 125AA (2005) and 5BB (2005), and located in southwestern Germany were examined for the existence of grapevine trunk disease (GTD) pathogens and related internal and external symptoms between 2011 and 2017. Frequency of leaf symptoms ranged from 0.2 % in six-year old blocks to appr. 1.5 % in 12-year-old blocks. While the typical tiger stripe pattern was less common, the majority of affected leaves was characterized by irregularly arranged necrotic spots spread over the leaf surface. Irrespective of leaf symptoms, in cross sections of 9-12 year old vines all sampled trunks (n ≥ 20 for each block) showed the typical GTD symptoms in the wood, with symptoms prevalent in the trunk head compared to the middle section and the basis of trunks. Pathogens were isolated from all trunks, with Fomitiporia mediterranea (Fmed), Cadophora luteo-olivacea (Clo), Phaeomoniella chlamydospora (Pch), Eutypa lata (Elata), and Phaeoacremonium aleophilum (Pal) being the most common. Other GTD species included Cadophora cf. novi-eboraci (new for German viticulture), Diaporthe eres, D. nobilis (new for German viticulture), D. rudis (new for German viticulture), Eutypa laevata (new for German viticiculture), Ilyonectria europaea, I. liriodendri, and Pestalotiopsis sp. The significance of the once found Sarocladium strictum remains unclear. GTD species were revealed from all sampled trunk parts, with maximum diversity and overall frequency in the trunk head. Further species, not related to GTDs, existed in all parts of the trunk. GTD pathogens were also demonstrated for all shoots (two shoots each of ten vines SO4, 125AA and 5BB, with five vines each externally symptomatic and non-symptomatic), but mostly could be detected by molecular means only. Clo, Pch, and Pal were the predominant species in shoots; further GTD species were Ilyonectria europaea, I. liriodendri, and Phaeoacremonium angustius.

Evaluation of long-term protection from nursery to vineyard provided by Trichoderma atroviride SC1 against fungal grapevine trunk pathogens.

Fungal grapevine trunk diseases (GTDs) represent a threat to viticulture, being responsible for important economic losses worldwide. Nursery and vineyard experiments were set up to evaluate the ability of Trichoderma atroviride SC1 to reduce infections of GTD pathogens in grapevine planting material during the propagation process and to assess the long-term protection provided by this biocontrol agent on grapevine plants in young vineyards during two growing seasons. Reductions of some GTD pathogen incidence and severity were found on grapevine propagation material after nursery application of T. atroviride SC1 during the grafting process, and also after additional T. atroviride SC1 treatments performed during two growing seasons in young vineyards, when compared with untreated plants. Trichoderma atroviride SC1 showed promise to reduce infections caused by some GTD pathogens in nurseries, and also when establishing new vineyards. This biological control agent could possibly be a valuable component in an integrated management approach where various strategies are combined to reduce GTD infections. © 2019 Society of Chemical Industry.

Phytoprotection potential of Fusarium proliferatum for control of Botryosphaeria dieback pathogens in grapevine

The economic impact of grapevine trunk diseases (GTDs) is increasing worldwide, due to the lack of efficient and simple control protocols for these disease complexes. Possible and efficient GTD management strategies must consider the complexity of host physiological alterations affecting metabolism and defense responses determined by GTD pathogens, and linked to disease expression. In this complexity, the use of biocontrol agents could give advantages in GTD control methods. The effect of the potential biocontrol agent (BCA) Fusarium proliferatum was evaluated using in vitro tests and in dual inoculation with the Botryosphaeria dieback agent Neofusicoc-cum parvum in planta. Artificial inoculations were performed in greenhouse and vineyard experiments at three key vine growth stages, the onset of G (separated clusters), I (flowering) or M (veraison) stages. The biocontrol potential was assessed using pathogenicity tests and transcriptomic analyses. Results showed that the F. proliferatum has potential for phytoprotection, with disease control efficiency related to host plant growth stage. Flowering was confirmed as the growth stage when disease control was least, and efficiency of activated defense responses against pathogen infection was minimum.

Draft Genome Sequences of Endophytic Pseudomonas spp. Isolated from Grapevine Tissue and Antagonistic to Grapevine Trunk Disease Pathogens

Endophytic strains of Pseudomonas were isolated from grapevine tissues and exhibited antagonistic activity against several grapevine trunk disease pathogens. The draft genome sequences of the four strains revealed the presence of putative gene clusters that may impart biocontrol activity against plant pathogens.

Soil microbiome analysis in an ESCA diseased vineyard

The soil microbiome is linked to the microbial ecosystem of aboveground plant tissues and it is able to modulate and stimulate plant responses. The community composition, i.e. diversity and abundance, is influenced by several factors such as agronomical practices, agrochemical practices and geographical location. For the first time, we present here the investigation of the microbial community related to the soil of a long-established cultivated vineyard using the meta-barcoding approach. Specifically, we analyzed the bacterial and fungal communities of the bulk soils associated with esca-symptomatic and asymptomatic vines. Results showed no significant differences in richness between the two types of samples. Conversely, we observed that esca-related pathogens and grapevine trunk disease (GTD) pathogens were more abundant in the bulk soils of symptomatic plants, suggesting that the soil could represent an important source of inoculum. We also identified two fungal genera, Curvularia and Coprinopsis, which are exclusive to the soil associated with asymptomatic plants. Moreover, Actinobacteria, a well-known group of bacteria symbionts, are over-represented in asymptomatic soils. Further studies are needed to expand the knowledge about these microorganisms, since they could have a role in controlling the development and/or spread of esca pathogens.

Grapevine Trunk Diseases Pathogens Identification on Grapevine Rootstocks in Ukraine

Grapevine Trunk Diseases Pathogens Identification on Grapevine Rootstocks in Ukraine

A protocol for the management of grapevine rootstock mother vines to reduce latent infections by grapevine trunk pathogens in cuttings

CITATION: Waite, H., et al. 2018. A protocol for the management of grapevine rootstock mother vines to reduce latent infections by grapevine trunk pathogens in cuttings. Phytopathologia Mediterranea, 57(3):84-398, doi:10.14601/Phytopathol_Mediterr-22772.

Grapevine trunk diseases under thermal and water stresses.

Heat and water stresses, individually or combined, affect both the plant (development, physiology, and production) and the pathogens (growth, morphology, dissemination, distribution, and virulence). The grapevine response to combined abiotic and biotic stresses is complex and cannot be inferred from the response to each single stress. Several factors might impact the response and the recovery of the grapevine, such as the intensity, duration, and timing of the stresses. In the heat/water stress-GTDs-grapevine interaction, the nature of the pathogens, and the host, i.e., the nature of the rootstock, the cultivar and the clone, has a great importance. This review highlights the lack of studies investigating the response to combined stresses, in particular molecular studies, and the misreading of the relationship between rootstock and scion in the relationship GTDs/abiotic stresses. Grapevine trunk diseases (GTDs) are one of the biggest threats to vineyard sustainability in the next 30years. Although many treatments and practices are used to manage GTDs, there has been an increase in the prevalence of these diseases due to several factors such as vineyard intensification, aging vineyards, or nursery practices. The ban of efficient treatments, i.e., sodium arsenite, carbendazim, and benomyl, in the early 2000s may be partly responsible for the fast spread of these diseases. However, GTD-associated fungi can act as endophytes for several years on, or inside the vine until the appearance of the first symptoms. This prompted several researchers to hypothesise that abiotic conditions, especially thermal and water stresses, were involved in the initiation of GTD symptoms. Unfortunately, the frequency of these abiotic conditions occurring is likely to increase according to the recent consensus scenario of climate change, especially in wine-growing areas. In this article, following a review on the impact of combined thermal and water stresses on grapevine physiology, we will examine (1) how this combination of stresses might influence the lifestyle of GTD pathogens, (2) learnings from grapevine field experiments and modelling aiming at studying biotic and abiotic stresses, and (3) what mechanistic concepts can be used to explain how these stresses might affect the grapevine plant status.

Electrolyzed acid water: A clean technology active on fungal vascular pathogens in grapevine nurseries

Phaeomoniella chlamydospora (Pc) and Phaeoacremonium minimum (Pm) are among the main grapevine trunk disease pathogens affecting vines in the nursery. These pathogens can cause infections of the propagation material often appearing as dark wood streaking, and are associated with decline occurrence in young vineyards. The infection may occur during the grafting process, particularly during hydration. Promising preliminary results were obtained in the nursery using electrolyzed acid water (EAW) for the hydration of cuttings; EAW is characterized by low values of pH (2.5), high oxidation reduction potential (ORP>1000) and a certain amount of free chlorine. No differences in absorption kinetics were recorded between EAW and tap water, nor among 1103P, K5BB and SO4 rootstocks. In all combinations no significant additional absorption was observed after 7 h of immersion. In order to assess the characteristics of EAW after the contact with the inner plant tissues ORP and pH were measured from the liquid extracted from rootstocks after immersion in EAW. The values of the liquid, named “weakened” EAW (wEAW) (625–650 mV ORP and 3.1–3.3 pH), were significantly different from the values of both EAW and the liquid extracted after immersion in tap water. When the propagation material was hydrated for 7 h in EAW no significant effect on vegetating growth performance and percentage of certifiable plants was observed for SO4 or 1103P, whereas a reduction in plant vegetative growth was observed in K5BB hydrated vines at 12hr hydration. EAW and wEAW gave no significant reduction of in vitro mycelial growth, whereas a consistent decrease in conidial germination was observed in Pc and Pm. The three-year experiments carried out in the nursery on cuttings inoculated with Pc and hydrated in EAW showed a remarkable reduction of the infection level in the treated plants.

Investigating the durable effect of the hot water treatment used in nurseries on pathogenic fungi inhabiting grapevine wood and involved in Grapevine Trunk Diseases

Hot water treatment (HWT) is used in nurseries to control pathogenic fungi involved in Grapevine Trunk Diseases (GTDs), as well as other pathogens, such as phytoplasmas. The long-term impact of this treatment on the entire microflora, especially on the general fungal microbiota living inside plants, still remains however unknown. In this study, the fungal microflora of vineyard plants, treated or not by HWT 14 and 15 years earlier were compared at different plant part levels. The fungal microflora was relatively abundant in the different types of wood tissues. Certain fungal genera were first isolated and then identified on the basis of their treatment or not by HWT. A significant change between 2010 and 2011, the two sampling years, was detected. Although the HWT may have affected the cuttings microflora at the nursery stage, this had not persisted after several years of HWT treatment for the fungi, especially the pathogenic ones. As HWT does not have a significant long-term control effect on GTD pathogens in mature plants in the vineyards, applying other sanitary methods as soon as HWT-young vines are planted in the vineyards is recommended.

Incidence of grapevine trunk diseases is influenced by soil, topology and vineyard age, but not by Diplodia seriata infection rate in the Tokaj Wine Region, Hungary

Grapevine Trunk Diseases (GTD) are of great importance worldwide, including Hungary, a Center European country with long wine producing history. Several GTD pathogens have been described till now in Europe, but only a few from Hungary. The presence of a GTD pathogen in the vine does not necessarily result in the immediate appearance of disease symptoms, and information on the importance of environmental factors related to disease incidence are still limited. The aim of this research was to assess the occurrence of GTD in the Tokaj Wine Region, and to determine the biotic and abiotic factors influencing disease incidence. Five vineyards within 15 km radius – each with different topology, soil types, varieties and age – were studied for three consecutive years (2013 – 2015). The incidence of GTD-infection was determined every year for each vineyard. Diplodia seriata was isolated with incidence ranging from 50 to 100%, while Diaporthe spp. were the only other – minor – GTD pathogen found. Topology and soil type appeared to be major abiotic factors affecting incidence of GTD symptom. Disease incidence was also positively correlating with the age of the vineyards, and it was in fact found to be the definitive biotic factor regarding incidence. In contrast, D. seriata infection rate appeared unrelated to disease incidence or to any of the biotic or abiotic factors investigated.

Protection of Grapevine Pruning Wounds against Eutypa lata by Biological and Chemical Methods

Eutypa dieback, caused by the fungus Eutypa lata, is a serious disease of grapevines that infects mainly through pruning wounds. The aim of this study was to evaluate the in vitro efficacy of fungicides from various chemical groups against E. lata, as well as the in vivo efficacy of the most effective fungicides and selected bacterial and fungal antagonists of E. lata, in grapevine pruning wound protection trials. In vitro studies revealed that flusilazole, tebuconazole, benomyl, fenarimol and myclobutanil were the most effective fungicides to inhibit mycelial growth of E. lata. Two field trials were conducted, one subjected to artificial inoculation and the second to natural infection only. In the first, benomyl, flusilazole and commercially available Trichoderma harzianum-containing products and an experimental Bacillus subtilis strain were applied to fresh pruning wounds. Two Cabernet Sauvignon vineyards were pruned in August 2001 and 2002 and immediately treated and inoculated with a spore suspension of E. lata one day later. Isolations were made from the treated pruning wounds after 12 months to assess the effectiveness of the treatments. The fungicides benomyl and flusilazole were the most effective treatments, although the Trichoderma treatments T77 and Trichoseal spray caused a significant reduction in E. lata infection. In a second trial, pruning wounds of Cabernet Sauvignon, Sauvignon blanc, Red Globe and Bonheur were treated with the Trichoderma products Vinevax (= Trichoseal spray) and Eco77 (= T77) in August 2005 and 2006, subjected to natural infection only and evaluated after seven months. Vinevax and Eco77 not only reduced E. lata, but they also reduced the incidence of other grapevine trunk disease pathogens.

Fungal trunk diseases: a problem beyond grapevines?

Grapevine trunk diseases (GTDs) are caused by a broad range of taxonomically unrelated fungi that occur wherever grapes are grown and are the main biotic factor limiting vineyard productivity and longevity (Bertsch et al., 2013). GTDs cause untenable economic losses to the grapevine industry worldwide. For example, they are considered a ‘national crisis’ in France, where it has been estimated that 12% of the vineyards are currently economically nonviable due to these maladies causing losses of about €1 billion (Lorch, 2014). Because GTDs are chronic and there is currently no option to eradicate the infections, unproductive vineyards must be replanted, at a worldwide annual cost estimate of €1·132 billion (Hofstetter et al., 2012). The establishment, progress, severity and spread of GTDs have been associated with (i) drought, (ii) limited availability of effective fungicides, (iii) pressure to increase yields, (iv) lack of pruning wound protection due to cost of labour, and/or (v) poor low-quality propagation material. Growers are demanding solutions. Many vineyards with high GTD incidence were planted in the mid-to-late 1990s, during which wine-grape prices were increasing (Volpe et al., 2008). These vineyards were being replanted in the wake of phylloxera, and nurseries could barely meet the demand for grape plants. In 2009 researchers declared the worldwide impact of GTDs and prioritized research goals (Bertsch et al., 2009). Despite scientific advances, there are still unanswered questions, for example about how the pathogens spread and which climate conditions favour infection. This limits the efficacy of GTD management practices. Other crops, such as almond, pistachio and walnut, are now experiencing planting booms (INC, 2015). The significance of these and other tree crops is that they host some of the same GTD pathogens. While researchers fine-tune strategies for managing GTDs in grape, the pathogens may alternate to tree crops, thus endangering the productivity and longevity of orchards and vineyards alike. Recent reports of high disease incidence in pome and stone fruits, nut crops, small fruits and olive in California (Úrbez-Torres et al., 2013), Iran (Mohammadi et al., 2015), Italy (Carlucci et al., 2015), South Africa (Cloete et al., 2011) and Spain (Gramaje et al., 2012) highlight the need for a focus on this new set of hosts. The production systems are different; not all practices for GTD management in grape are feasible in tree crops, especially with dwindling numbers of skilled farm labourers. Tree crop nurseries are struggling to meet demands for plant material and, from our experience with GTDs, a lack of first-quality plants means that low-quality plants are sold, too. Are these plantings doomed to a lifetime of poor productivity? Is the sustainability of the fruit and tree nut industries at risk? Yours sincerely, David Gramaje et al.

Effectiveness of Natural Antifungal Compounds in Controlling Infection by Grapevine Trunk Disease Pathogens through Pruning Wounds.

Grapevine trunk fungal pathogens, such as Diplodia seriata and Phaeomoniella chlamydospora, can infect plants through pruning wounds. They cause grapevine trunk diseases and are involved in grapevine decline. Accordingly, the protection of pruning wounds is crucial for the management of grapevine trunk diseases. The efficacy of different natural antifungals in inhibiting the growth of several fungi causing grapevine trunk diseases was evaluated in vitro. The fungi showing greater in vitro efficacy were tested on autoclaved grape wood assays against D. seriata and P. chlamydospora. Based on results from these assays, chitosan oligosaccharide, vanillin, and garlic extract were selected for further evaluation on pruning wounds inoculated with D. seriata and P. chlamydospora in field trials. A significant decrease in plant mortality was observed after 2 years of growth in the plants treated with the different natural antifungals compared to the mortality rate observed in infected plants that were not treated with antifungals. Also, the infection rate for the inoculated pathogens was significantly reduced in plants treated with the selected natural antifungals. Therefore, natural antifungals represent a promising alternative for disease control and could provide significant economic benefits for the grape-growing industry.

Arthropods Vector Grapevine Trunk Disease Pathogens

Arthropod-mediated dispersal of pathogens is known in many cropping systems but has never been demonstrated for grapevine trunk disease pathogens. Arthropods from vineyards were screened for the presence of pathogens associated with Petri disease and esca using cultural and molecular techniques. The ability of the most abundant pathogen-carrying species to inoculate healthy grapevine vascular tissues was also determined. Millipedes and ants were allowed to associate with a DsRed- Express-transformed Phaeomoniella chlamydospora, after which they were exposed to freshly pruned healthy grapevines under controlled conditions and wounds were monitored for subsequent infection. In addition, the possibility of millipede excreta, commonly found on pruning wounds in the field, to act as inoculum source was determined. A diverse arthropod fauna was associated with declining grapevines and many of these carried trunk disease pathogens. However, spiders, the ant Crematogaster peringueyi, and the millipede Ommattoiulus moreleti were the most abundant pathogen carriers. The ant and millipede species fed on pruning wound sap and effectively transmitted trunk disease pathogens. Millipede excreta contained viable spores of Phaeomoniella chlamydospora and may serve as an inoculum source. Numerous arthropods, including beneficial predators, are potential vectors of grapevine trunk disease pathogens. Our results highlight the need for an integrated approach, including targeted management of ants and millipedes at the time of pruning, to limit the spread of grapevine trunk diseases.

Phomopsis Dieback: A Grapevine Trunk Disease Caused by Phomopsis viticola in California.

Field surveys recently conducted in California and in other grape-growing regions in the United States showed Phomopsis viticola to be one of the most prevalent fungi isolated from grapevine perennial cankers in declining vines. The current study has not only confirmed the presence of P. viticola from grapevine cankers in California but also has for the first time revealed the occurrence of Diaporthe ambigua, D. eres, and D. neotheicola in symptomatic grapevine wood in California by means of morphological studies and multi-gene sequence analysis. Pathogenicity trials conducted on mature cordons of Vitis vinifera 'Syrah' and 'Red Globe', as well as on lignified Syrah dormant canes, showed P. viticola isolates from California to be capable of causing perennial cankers. Lengths of vascular discoloration caused by P. viticola were similar to those caused by Eutypa lata and several Botryosphaeriaceae spp., which are well-known grapevine trunk disease pathogens. Additionally, a lack of spring growth was commonly observed in dormant canes inoculated with P. viticola spore suspensions in two pathogenicity trials. As part of this study, V. vinifera 'Cabernet Sauvignon' and 'Zinfandel' wood was shown to be more susceptible to infection by P. viticola than 'Barbera', 'Chardonnay', 'Merlot', and 'Thompson Seedless' wood. After more than 40 years overlooking P. viticola as a grapevine wood pathogen, this study provides strong evidence of the role of P. viticola as a canker-causing organism, and suggests its addition to the fungi involved in the grapevine trunk disease complex. Results from this study suggest D. ambigua and D. neotheicola to be saprophytes or weak pathogens on grapevine wood.