Seasonal Susceptibility of Grapevine Pruning Wounds and Cane Colonization in Catalonia, Spain Following Artificial Infection with Diplodia seriata and Phaeomoniella chlamydospora

Arthropods as Vectors of Grapevine Trunk Disease Pathogens: Quantification of Phaeomoniella chlamydospora on Arthropods and Mycobiome Analysis of Earwig Exoskeletons

Viticulture worldwide is challenged by grapevine trunk diseases (GTDs). Involvement of arthropods in the dissemination process of GTD pathogens, notably esca pathogens, is indicated after detection of associated pathogens on arthropod exoskeletons, and demonstration of transmission under artificial conditions. The present study is the first to quantify spore loads via qPCR of the esca-relevant pathogen Phaeomoniella chlamydospora on arthropods collected in German vineyards, i.e., European earwigs (Forficula auricularia), ants (Formicidae), and two species of jumping spiders (Marpissa muscosa and Synageles venator). Quantification of spore loads showed acquisition on exoskeletons, but most arthropods carried only low amounts. The mycobiome on earwig exoskeletons was described for the first time to reveal involvement of earwigs in the dispersal of GTDs in general. Metabarcoding data support the potential risk of earwigs as vectors for predominantly Pa. chlamydospora and possibly Eutypa lata (causative agent of Eutypa dieback), as respective operational taxonomical unit (OTU) assigned genera had relative abundances of 6.6% and 2.8% in total reads, even though with great variation between samples. Seven further GTD-related genera were present at a very low level. As various factors influence the successful transmission of GTD pathogens, we hypothesize that arthropods might irregularly act as direct vectors. Our results highlight the importance of minimizing and protecting pruning wounds in the field.

Variability of Functional Groups of Rhizosphere Fungi of Norway Spruce (Picea abies (L.) H.Karst.) in the Boreal Range: The Wigry National Park, Poland

Rhizosphere microbial communities can influence plant growth and development. Natural regeneration processes take place in the tree stands of protected areas, which makes it possible to observe the natural changes taking place in the rhizosphere along with the development of the plants. This study aimed to determine the diversity (taxonomic and functional) of the rhizosphere fungal communities of Norway spruce growing in one of four developmental stages. Our research was based on the ITS region using Illumina system sequencing. Saprotrophs dominated in the studied rhizospheres, but their percentage share decreased with the age of the development group (for 51.91 from 43.13%). However, in the case of mycorrhizal fungi, an opposite trend was observed (16.96-26.75%). The most numerous genera were: saprotrophic Aspergillus (2.54-3.83%), Penicillium (6.47-12.86%), Pyrenochaeta (1.39-11.78%), pathogenic Curvularia (0.53-4.39%), and mycorrhizal Cortinarius (1.80-5.46%), Pseudotomentella (2.94-5.64%) and Tomentella (4.54-15.94%). The species composition of rhizosphere fungal communities was favorable for the regeneration of natural spruce and the development of multi-generational Norway spruce stands. The ratio of the abundance of saprotrophic and mycorrhizal fungi to the abundance of pathogens was high and promising for the durability of the large proportion of spruce in the Wigry National Park and for forest ecosystems in general.

Susceptibility of pruning wounds to grapevine trunk diseases: A quantitative analysis of literature data

INTRODUCTION

Pruning wounds are the main entry points for fungi causing grapevine trunk diseases (GTDs). Several studies identified factors influencing the temporal dynamics of wound susceptibility, which include the fungal species and inoculum dose, weather conditions, grape variety, pruning date, and so forth. Here, we conducted a quantitative analysis of literature data to synthesise outcomes across studies and to identify the factors that most affect the length of pruning wound susceptibility.

METHODS

We extracted data on the frequency at which the inoculated wounds showed GTD symptoms or an inoculated pathogen was reisolated following artificial inoculation at the time of pruning or in the following days. A negative exponential model was fit to these data to describe changes in wound susceptibility as a function of time since pruning, in which the rate parameter changed depending on specific factors.

RESULTS AND DISCUSSION

The results show that wound susceptibility is high at the time of pruning, and they remain susceptible to invasion by GTD fungi for months after pruning. Infection incidence on wounds was higher for fungi associated with Botryosphaeria dieback than those associated with Eutypa dieback or Esca complex, and wound susceptibility decreased faster for Eutypa dieback than for other GTD agents. Grapevine variety and pruning season also affected the wound susceptibility period. Sauvignon Blanc remains susceptible to GTDs longer than other varieties. We also found that the time of pruning can affect infection dynamics, especially for more susceptible varieties. The results increase our understanding of GTD epidemiology and should help growers control infections.

Duration of the susceptibility of pruning wounds of different ages to infections by Phaeomoniella chlamydospora on grapevine cv. Cabernet Sauvignon in Central Chile

Grapevine trunk diseases (GTDs) are one of the most important phytosanitary problems that affect grapevines (Vitis vinifera) worldwide. In Chile, Phaeomoniella chlamydospora is the major fungal trunk pathogen associated with GTDs. In the vineyards, the natural infections by P. chlamydospora are associated with air-borne conidia dispersed onto fresh pruning wounds from pycnidia. These pruning wounds are considered an important entrance for fungal trunk pathogens such as P. chlamydospora in the host in the field. However, the duration of the susceptibility of grapevine annual pruning wounds to P. chlamydospora is still unknown in Chile. Therefore, this study aimed to evaluate the period of susceptibility of pruning wounds of different ages to artificial infection of P. chlamydospora on grapevine cv. Cabernet Sauvignon, Central Chile. Artificial inoculations of a conidial suspension (105 conidia/mL) of P. chlamydospora were used to determine the susceptibility of pruning wounds of different ages, from 1, 15, 30, and 45 days after pruning. The experiments were conducted on lignified cuttings in a greenhouse, and on vine spurs in two vineyards (Buin and Nancagua, Central Chile) during two consecutive seasons. The results indicated that the pruning wounds of grapevine cv. Cabernet Sauvignon were very susceptible to infections by P. chlamydospora, with a percentage of pruning wounds infected from 97 to 71% for cuttings, and 96% to 60% for spurs, during the first 15 days after pruning. However, the susceptibility of pruning wounds of different ages in cuttings and spurs of grapevine, generally decreased as the time from pruning to inoculation increased. Moreover, the pruning wounds the pruning wounds remained susceptible to artificial inoculation by P. chlamydospora for up 45 days after pruning with percent of wounds infected from 8.0 to 12.2, and 8.3 to 18.8% on cuttings and spurs of grapevine, respectively. Finally, this study constitutes study constitutes the first research focalized on the susceptibility of pruning wounds of various ages of grapevine cv. Cabernet Sauvignon to artificial inoculations by P. chlamydospora in Central Chile.

Mixed infections of fungal trunk pathogens and induced systemic phenolic compound production in grapevines

As grapevines mature in California vineyards they accumulate chronic wood infections by the Ascomycete fungi that cause trunk diseases, including Botryosphaeria dieback (caused by Diplodia seriata and Neofusicoccum parvum) and Esca (caused by Phaeomoniella chlamydospora). It is thought that such mixed infections become localized to separate internal lesions/cankers of the permanent, woody structure of an individual vine, but nonetheless the fungi all colonize the same vascular system. In response to infection by one pathogen, the host may initiate systemic biochemical changes, which in turn may affect the extent of subsequent infections by other pathogens. To test this hypothesis, we measured changes in phenolic compounds in the wood and lesion lengths of the pathogens, during sequential co-inoculations with different or identical pair-wise sequences of infection by D. seriata, N. parvum, or P. chlamydospora. Prior fungal infections only affected the development of subsequent D. seriata infections. Effects of fungal infections on phenolic compounds were variable, yet initial infection by D. seriata was associated with significantly higher concentrations of most phenolic compounds distally, compared to all other initial inoculation treatments. It was hypothesized that pre-existing phenolic levels can slow initial lesion development of fungal trunk pathogens, especially for D. seriata, but over time the pathogens appeared to overcome or neutralize phenolic compounds and grow unimpeded. These results demonstrate that effects of one fungal trunk pathogen infection is generally unable to distally affect another long-term, albeit shifts in host phenolics and other plant defenses do occur.

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.

Activity of Trichoderma asperellum Strain ICC 012 and Trichoderma gamsii Strain ICC 080 Toward Diseases of Esca Complex and Associated Pathogens

Grapevine trunk diseases are widespread in all grape-growing countries. The diseases included in the Esca complex of diseases are particularly common in European vineyards. Their distinctive foliar symptoms are well known to be associated not only with losses in quantity, as with all grapevine wood diseases, but also with losses in the quality of the crop. Protection of pruning wounds is known to reduce infections in artificial inoculations and, to some extent, reduce the external leaf symptoms. The application of biological control agents in the field is typically started at the first appearance of symptoms. In this article, the two strains belonging to two different species, Trichoderma asperellum ICC 012 and T. gamsii ICC 080, which are present in a commercial formulation, were tested in vitro, in vivo in artificial inoculation, and in the field in long-term experiments where the wounds on four young asymptomatic vineyards were protected since 1 or 2 years after planting. The in vitro trials highlighted the different temperature requirements of the two strains, the direct mycoparasitizing activity of T. asperellum, and the indirect activity shown by both Trichoderma strains. The in vivo trials confirmed the ability of the two strains to reduce the colonization following artificial inoculations with the high, unnatural concentration of spores used in artificial infections, even if with variable efficacy, and with long persistence as they could be reisolated 7 months post-application. The preventive applications carried out over 9 years showed a very high reduction in symptom development in the treated vines, on annual and cumulated incidence and on the death of vines, with disease reduction varying from 66 to almost 90%. Early and annual application of protection to the pruning wounds appears to be the best method for reducing damages caused by grapevine leaf stripe disease (a disease of the Esca complex of diseases). Trichoderma appears to offer an efficient, environmentally friendly, and long-lasting protection in the presence of a natural inoculum concentration.

Temporal Dispersal Patterns of Phaeomoniella chlamydospora, Causal Agent of Petri Disease and Esca, in Vineyards

Although the fungus Phaeomoniella chlamydospora is the most commonly detected causal agent of Petri disease and esca, two important fungal grapevine trunk diseases, little is known about the dispersal patterns of P. chlamydospora inoculum. In this work, we studied the dispersal of P. chlamydospora airborne inoculum from 2016 to 2018 in two viticultural areas of eastern (Ontinyent) and northern (Logroño) Spain. The vineyards were monitored weekly from November to April using microscope slide traps, and P. chlamydospora was detected and quantified by a specific real-time quantitative (qPCR) method set up in this work. The method was found to be sensitive, and a good correlation was observed between numbers of P. chlamydospora conidia (counted by microscope) and DNA copy numbers (quantified by qPCR). We consistently detected DNA of P. chlamydospora at both locations and in all seasons but in different quantities. In most cases, DNA was first detected in the last half of November, and most of the DNA was detected from December to early April. When rain was used as a predictor of P. chlamydospora DNA detection in traps, false-negative detections were observed, but these involved only 4% of the total. The dispersal pattern of P. chlamydospora DNA over time was best described (R² = 0.765 and concordance correlation coefficient = 0.870) by a Gompertz equation, with time expressed as hydrothermal time (a physiological time accounting for the effects of temperature and rain). This equation could be used to predict periods with a high risk of dispersal of P. chlamydospora.

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

BACKGROUND

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.

RESULTS

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.

CONCLUSION

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.

Characterization and Pathogenicity of Botryosphaeriaceae Fungi Associated with Declining Urban Stands of Coast Redwood in California

Coast redwood (Sequoia sempervirens) is among the most widely planted landscape trees in California (CA) but is in decline outside its natural range due to factors including prolonged drought and plant pathogens. We investigated associations of Botryosphaeriaceae fungi with declining coast redwood trees throughout CA. More than 100 samples were collected from 11 coastal and inland locations in CA. Fifty-nine Botryosphaeria-like fungal strains were isolated and 18 were selected for further study. Phylogenetic analysis of ITS and EF-1α sequence data confirmed the presence of Botryosphaeria dothidea, Neofusicoccum australe, N. luteum, N. mediterraneum, and N. parvum. Pathogenicity testing showed that although the Neofusicoccum species vary in virulence, all are more virulent that B. dothidea. N. australe caused the largest lesions, followed by N. luteum, N. parvum, and N. mediterraneum. Of the species recovered, only B. dothidea has been previously confirmed as a pathogen of coast redwood in CA. These results confirm that multiple Botryosphaeriaceae species are associated with branch decline and dieback on coast redwood in CA, which agrees with similar studies on woody agricultural crops. Accurate diagnosis of fungal pathogens of coast redwood is important for the development of disease management strategies and may help improve horticultural practices in maintenance of urban stands.

Managing Grapevine Trunk Diseases With Respect to Etiology and Epidemiology: Current Strategies and Future Prospects

Fungal trunk diseases are some of the most destructive diseases of grapevine in all grape growing areas of the world. Management of GTDs has been intensively studied for decades with some great advances made in our understanding of the causal pathogens, their epidemiology, impact, and control. However, due to the breadth and complexity of the problem, no single effective control measure has been developed. Management of GTD must be holistic and integrated, with an interdisciplinary approach conducted in both nurseries and vineyards that integrates plant pathology, agronomy, viticulture, microbiology, epidemiology, biochemistry, physiology, and genetics. In this review, we identify a number of areas of future prospect for effective management of GTDs worldwide, which, if addressed, will provide a positive outlook on the longevity of vineyards in the future.