Grapevines under drought do not express esca leaf symptoms

Monitoring the phenology of plant pathogenic fungi: why and how?

Phenology is a key adaptive trait of organisms, shaping biotic interactions in response to the environment. It has emerged as a critical topic with implications for societal and economic concerns due to the effects of climate change on species' phenological patterns. Fungi play essential roles in ecosystems, and plant pathogenic fungi have significant impacts on global food security. However, the phenology of plant pathogenic fungi, which form a huge and diverse clade of organisms, has received limited attention in the literature. This diversity may have limited the use of a common language for comparisons and the integration of phenological data for these taxonomic groups. Here, we delve into the concept of 'phenology' as applied to plant pathogenic fungi and explore the potential drivers of their phenology, including environmental factors and the host plant. We present the PhenoFun scale, a phenological scoring system suitable for use with all fungi and fungus-like plant pathogens. It offers a standardised and common tool for scientists studying the presence, absence, or predominance of a particular phase, the speed of phenological phase succession, and the synchronism shift between pathogenic fungi and their host plants, across a wide range of environments and ecosystems. The application of the concept of 'phenology' to plant pathogenic fungi and the use of a phenological scoring system involves focusing on the interacting processes between the pathogenic fungi, their hosts, and their biological, physical, and chemical environment, occurring during the life cycle of the pathogen. The goal is to deconstruct the processes involved according to a pattern orchestrated by the fungus's phenology. Such an approach will improve our understanding of the ecology and evolution of such organisms, help to understand and anticipate plant disease epidemics and their future evolution, and make it possible to optimise management models, and to encourage the adoption of cropping practices designed from this phenological perspective.

Mechanisms of grapevine resilience to a vascular disease: investigating stem radial growth, xylem development and physiological acclimation

BACKGROUND AND AIMS

Plant vascular diseases significantly impact crop yield worldwide. Esca is a vascular disease of grapevine found globally in vineyards which causes a loss of hydraulic conductance due to the occlusion of xylem vessels by tyloses. However, the integrated response of plant radial growth and physiology in maintaining xylem integrity in grapevine expressing esca symptoms remains poorly understood.

METHODS

We investigated the interplay between variation in stem diameter, xylem anatomy, plant physiological response and hydraulic traits in two widespread esca-susceptible cultivars, 'Sauvignon blanc' and 'Cabernet Sauvignon'. We used an original experimental design using naturally infected mature vines which were uprooted and transplanted into pots allowing for their study in a mini-lysimeter glasshouse phenotyping platform.

KEY RESULTS

Esca significantly altered the timing and sequence of stem growth periods in both cultivars, particularly the shrinkage phase following radial expansion. Symptomatic plants had a significantly higher density of occluded vessels and lower leaf and whole-plant gas exchange. Esca-symptomatic vines showed compensation mechanisms, producing numerous small functional xylem vessels later in development suggesting a maintenance of stem vascular cambium activity. Stabilization or late recovery of whole-plant stomatal conductance coincided with new healthy shoots at the top of the plant after esca symptoms plateaued.

CONCLUSIONS

Modified cropping practices, such as avoiding late-season topping, may enhance resilience in esca-symptomatic plants. These results highlight that integrating dendrometers, xylem anatomy and gas exchange provides insights into vascular pathogenesis and its effects on plant physiology.

Plant hydraulics at the heart of plant, crops and ecosystem functions in the face of climate change

Plant hydraulics is crucial for assessing the plants' capacity to extract and transport water from the soil up to their aerial organs. Along with their capacity to exchange water between plant compartments and regulate evaporation, hydraulic properties determine plant water relations, water status and susceptibility to pathogen attacks. Consequently, any variation in the hydraulic characteristics of plants is likely to significantly impact various mechanisms and processes related to plant growth, survival and production, as well as the risk of biotic attacks and forest fire behaviour. However, the integration of hydraulic traits into disciplines such as plant pathology, entomology, fire ecology or agriculture can be significantly improved. This review examines how plant hydraulics can provide new insights into our understanding of these processes, including modelling processes of vegetation dynamics, illuminating numerous perspectives for assessing the consequences of climate change on forest and agronomic systems, and addressing unanswered questions across multiple areas of knowledge.

Integrated metabolomics and transcriptomics analysis reveals that the change of apoplast metabolites contributes to adaptation to winter freezing stress in Euonymus japonicus

Euonymus japonicus, a common urban street tree, can withstand winter freezing stress in temperate regions. The apoplast is the space outside the plasma membrane, and the changes of metabolites in apoplast may be involved in plant adaptation to adverse environments. To reveal the molecular mechanism underlying the winter freezing stress tolerance in E. japonicus, the changes in physiological and biochemical indexes, apoplast metabolites, and gene expression in the leaves of E. japonicus in early autumn and winter were analyzed. A total of 300 differentially accumulated metabolites were identified in apoplast fluids in E. japonicus, which were mainly related to flavone and flavonol biosynthesis, and galactose metabolism, amino acid synthesis, and unsaturated fatty acid synthesis. Integrated metabolomics and transcriptomics analysis revealed that E. japonicus adjust apoplast metabolites including flavonoids such as quercetin and kaempferol, and oligosaccharides such as raffinose and stachyose, to adapt to winter freezing stress through gene expression regulation. In addition, the regulation of ABA and SA biosynthesis and signal transduction pathways, as well as the activation of the antioxidant enzymes, also played important roles in the adaptation to winter freezing stress in E. japonicus. The present study provided essential data for understanding the molecular mechanism underlying the adaptation to winter freezing stress in E. japonicus.

Hybrid Vitis Cultivars with American or Asian Ancestries Show Higher Tolerance towards Grapevine Trunk Diseases

Grape production worldwide is increasingly threatened by grapevine trunk diseases (GTDs). No grapevine cultivar is known to be entirely resistant to GTDs, but susceptibility varies greatly. To quantify these differences, four Hungarian grape germplasm collections containing 305 different cultivars were surveyed to determine the ratios of GTDs based on symptom expression and the proportion of plant loss within all GTD symptoms. The cultivars of monophyletic Vitis vinifera L. origin were amongst the most sensitive ones, and their sensitivity was significantly (p < 0.01) higher than that of the interspecific (hybrid) cultivars assessed, which are defined by the presence of Vitis species other than V. vinifera (e.g., V. labrusca L., V. rupestris Scheele, and V. amurensis Rupr.) in their pedigree. We conclude that the ancestral diversity of grapes confers a higher degree of resilience against GTDs.

Quantifying the grapevine xylem embolism resistance spectrum to identify varieties and regions at risk in a future dry climate

Maintaining wine production under global warming partly relies on optimizing the choice of plant material for a given viticultural region and developing drought-resistant cultivars. However, progress in these directions is hampered by the lack of understanding of differences in drought resistance among Vitis genotypes. We investigated patterns of xylem embolism vulnerability within and among 30 Vitis species and sub-species (varieties) from different locations and climates, and assessed the risk of drought vulnerability in 329 viticultural regions worldwide. Within a variety, vulnerability to embolism decreased during summer. Among varieties, we have found wide variations in drought resistance of the vascular system in grapevines. This is particularly the case within Vitis vinifera, with varieties distributed across four clusters of embolism vulnerability. Ugni blanc and Chardonnay featured among the most vulnerable, while Pinot noir, Merlot and Cabernet Sauvignon ranked among the most resistant. Regions possibly at greater risk of being vulnerable to drought, such as Poitou-Charentes, France and Marlborough, New Zealand, do not necessarily have arid climates, but rather bear a significant proportion of vulnerable varieties. We demonstrate that grapevine varieties may not respond equally to warmer and drier conditions, and highlight that hydraulic traits are key to improve viticulture suitability under climate change.

Esca grapevine disease involves leaf hydraulic failure and represents a unique premature senescence process

Xylem anatomy may change in response to environmental or biotic stresses. Vascular occlusion, an anatomical modification of mature xylem, contributes to plant resistance and susceptibility to different stresses. In woody organs, xylem occlusions have been examined as part of the senescence process, but their presence and function in leaves remain obscure. In grapevine, many stresses are associated with premature leaf senescence inducing discolorations and scorched tissue in leaves. However, we still do not know whether the leaf senescence process follows the same sequence of physiological events and whether leaf xylem anatomy is affected in similar ways. In this study, we quantified vascular occlusions in midribs from leaves with symptoms of the grapevine disease esca, magnesium deficiency and autumn senescence. We found higher amounts of vascular occlusions in leaves with esca symptoms (in 27% of xylem vessels on average), whereas the leaves with other symptoms (as well as the asymptomatic controls) had far fewer occlusions (in 3% of vessels). Therefore, we assessed the relationship between xylem occlusions and esca leaf symptoms in four different countries (California in the USA, France, Italy and Spain) and eight different cultivars. We monitored the plants over the course of the growing season, confirming that vascular occlusions do not evolve with symptom age. Finally, we investigated the hydraulic integrity of leaf xylem vessels by optical visualization of embolism propagation during dehydration. We found that the occlusions lead to hydraulic dysfunction mainly in the peripheral veins compared with the midribs in esca symptomatic leaves. These results open new perspectives on the role of vascular occlusions during the leaf senescence process, highlighting the uniqueness of esca leaf symptoms and its consequence on leaf physiology.

Sodium arsenite-induced changes in the wood of esca-diseased grapevine at cytological and metabolomic levels

In the past, most grapevine trunk diseases (GTDs) have been controlled by treatments with sodium arsenite. For obvious reasons, sodium arsenite was banned in vineyards, and consequently, the management of GTDs is difficult due to the lack of methods with similar effectiveness. Sodium arsenite is known to have a fungicide effect and to affect the leaf physiology, but its effect on the woody tissues where the GTD pathogens are present is still poorly understood. This study thus focuses on the effect of sodium arsenite in woody tissues, particularly in the interaction area between asymptomatic wood and necrotic wood resulting from the GTD pathogens' activities. Metabolomics was used to obtain a metabolite fingerprint of sodium arsenite treatment and microscopy to visualize its effects at the histo-cytological level. The main results are that sodium arsenite impacts both metabolome and structural barriers in plant wood. We reported a stimulator effect on plant secondary metabolites in the wood, which add to its fungicide effect. Moreover, the pattern of some phytotoxins is affected, suggesting the possible effect of sodium arsenite in the pathogen metabolism and/or plant detoxification process. This study brings new elements to understanding the mode of action of sodium arsenite, which is useful in developing sustainable and eco-friendly strategies to better manage GTDs.

Long-Term Esca Monitoring Reveals Disease Impacts on Fruit Yield and Wine Quality

Esca is a widespread grapevine trunk disease, and a global increase in esca incidence has been observed in recent decades. Estimates attribute considerable economic losses to esca, and the disease is considered one of the major causes of vine mortality and vineyard dieback. However, accurate quantification of esca incidence is difficult due to symptom inconsistency, and there are very few studies precisely quantifying yield losses and impacts on fruit composition and wine quality. This study carried out an extensive esca surveying program; annually monitoring approximately 57,000 vines across 12 estates in the Bordeaux region for 9 years. In conjunction with this surveying program, we quantified the yield losses of vines with known esca symptom histories and assessed their fruit composition and resulting wine quality. The study revealed that, because of year-to-year variation in symptom expression, accurate rates of esca can only be obtained through monitoring over many years. We found that yield losses in individual vines exhibiting esca can reach up to 50% but they are rarely unproductive, and when scaled to the parcel scale yield losses are low, never exceeding 1 hl/ha. In addition, the quality of the grapes produced is similar to that obtained from vines without symptoms. Finally, the majority of mortality observed in vineyards was not due to esca, with only 40% of dead vines exhibiting an esca history. These results suggest that the impact of esca is likely overestimated and that it is necessary to more broadly investigate other factors contributing to vine mortality and vineyard dieback.[Formula: see text] Copyright © 2022 The Author(s). This is an open-access article distributed under the CC BY 4.0 International license.

Interactions of the Fungal Community in the Complex Patho-System of Esca, a Grapevine Trunk Disease

Worldwide, Esca is a complex and devastating Grapevine Trunk Disease (GTD), characterized by inconstant foliar symptoms and internal wood degradation. A large range of fungal taxa have been reported as causal agents. We applied both culture-dependent and culture-independent methods (Illumina Technology and q-PCR) to investigate this concerning disease. Woods from vines with asymptomatic leaves and vines with leaf Esca symptoms were compared. Internally, different types of wood were found, from healthy wood with black necrosis to wood with white rot. A combination of leaf and wood Esca symptoms resulted in four experimental categories. Although there was no relation with symptoms, culture-independent mycobiome composition revealed Phaeomoniella chlamydospora, a GTD pathogen, as the most abundant species (detected in 85.4% of wood samples, with 14.8% relative abundance). Using TaqMan q-PCR, P. chlamydospora DNA was detected in 60.4% of samples (far from the 18.8% of positive results in the culture-dependent approach). There was a predominance of saprotrophs, even if their abundance was not affected by Esca symptoms. Concerning pathotrophs, the white rot development within grapevines was linked to the abundance of fungi belonging to the Hymenochaetaceae family. The Botryosphaeriaceae family was identified as an indicator for expression of Esca foliar symptoms. Lastly, the Aureobasidiaceae family was found to be a potential biocontrol agent for Esca, since it was most abundant in the control asymptomatic plants.

Fungal Grapevine Trunk Diseases in Romanian Vineyards in the Context of the International Situation

Vitis vinifera, known as the common grape vine, represents one of the most important fruit crops in the world. Romania is a wine-producing country with a rich and long tradition in viticulture. In the last decade, increasing reports of damage caused by grapevine trunk diseases (GTDs) have raised concerns in all wine producing countries. Up to now, no study was performed regarding the GTDs situation in Romania, an important grapevine grower in Europe. In this study, we aim, after a comprehensive presentation of the fungal GTDs worldwide, to review the scientific information related to these diseases in Romania in order to open a national platform in an international framework. In order to achieve this, we consulted over 500 references from different scientific databases and cited 309 of them. Our review concludes that, in Romania, there is little amount of available literature on this matter. Three out of six fungal GTDs are reported and well documented in all of the Romanian viticultural zones (except for viticultural zone 4). These are Eutypa dieback, Phomopsis dieback, and Esca disease. Of the fungal pathogens considered responsible Eutypa lata, Phomopsis viticola and Stereum hirsutum are the most studied and well documented in Romania. Management measures are quite limited, and they mostly include preventive measures to stop the GTDs spread and the removal of affected grapevines.

Physiological and Molecular Responses of Vitis vinifera cv. Tempranillo Affected by Esca Disease

Esca is a multi-fungal disease affecting grapevines. The objective of the study was to evaluate the physiological and molecular response of the grapevine cv. Tempranillo to esca disease, carried out in a vineyard under Mediterranean climatic conditions in western Spain. The photosynthetic pigments in the leaves decreased, with a strong decrease in the photosynthetic efficiency. The proline content increased significantly in the early stages of affected leaves, being possibly involved in the maintenance of lipid peroxidation levels in leaves, which do not increase. The phenol, flavonoid, and phenylpropanoid content decreased in esca-affected leaves, as does the total antioxidant capacity (FRAP), while the polyphenol oxidase (PPO) activity suffers a strong increase with the development of the disease. In affected grapes, the lipid peroxidation and the total phenol content decrease, but not the anthocyanin content. The ascorbate pool decreases with the disease and with time. On the other hand, pool GSH + GSSG is lower in affected leaves, but increases with time. These alterations show a clear change in the redox homeostasis. The expression of genes phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), superoxide dismutase (SOD), and chalcone synthase (ChaS1 and ChaS3) become considerably higher in response to esca, being even higher when the infection time increases. The alteration of AsA and GSH levels, phenolic compounds, PPO activity, proline content, and FRAP, together with the increase of the PAL, PPO, SOD,ChaS1, and ChaS3 gene expression, are clearly implicated in the esca response in plants. The expression of these genes, similar to the PPO activity, can be used as markers of state in the development of the disease.

Guarding and hijacking: stomata on the move

Stomata-pathogen interactions are a fascinating part of plant immunity. Stomata perceive pathogens and close; in turn, successful pathogens reopen stomata to enter the apoplast. Recent studies by Hu et al. and Roussin-Léveillée et al. demonstrate that, following entry, Pseudomonas syringae closes stomata and, thus, reduces transpiration in infected leaves, adding another layer of complexity to the stomata-pathogen interaction.

Water Deficit Timing Differentially Affects Physiological Responses of Grapevines Infected with Lasiodiplodia theobromae

Diseases and climate change are major factors limiting grape productivity and fruit marketability. Lasiodiplodia theobromae is a fungus of the family Botryosphaeriaceae that causes Botryosphaeria dieback of grapevine worldwide. Abiotic stress may change host vitality and impact susceptibility to the pathogen and/or change the pathogen's life cycle. However, the interaction between both stress drivers is poorly understood for woody plants. We addressed the hypothesis that distinct morpho-physiological and biochemical responses are induced in grapevine (Vitis vinifera)-L. theobromae interactions depending on when water deficits are imposed. Grapevines were submitted to water deficit either before or after fungus inoculation. Water deficit led to the reduction of the net photosynthetic rate, stomatal conductance, and transpiration rate, and increased the abscisic acid concentration regardless of fungal inoculation. L. theobromae inoculation before water deficit reduced plant survival by 50% and resulted in the accumulation of jasmonic acid and reductions in malondialdehyde levels. Conversely, grapevines inoculated after water deficit showed an increase in proline and malondialdehyde content and all plants survived. Overall, grapevines responded differently to the primary stress encountered, with consequences in their physiological responses. This study reinforces the importance of exploring the complex water deficit timing × disease interaction and the underlying physiological responses involved in grapevine performance.

Pathogen-induced hydraulic decline limits photosynthesis and starch storage in grapevines (Vitis sp.)

Xylella fastidiosa (Xf) is the bacterial pathogen responsible for Pierce's Disease (PD) in grapevine (Vitis vinifera L.) and numerous diseases in agriculturally and ecologically important species. Current theory suggests that localized inoculations via insect feeding lead to bacterial spread through the xylem, reducing water transport capacity, leading to declines in productivity, and ultimately death. Yet, the underlying mechanisms of Xf-induced mortality are not fully understood. In this study, we documented the development of PD symptoms over 12-13 weeks postinoculation. Subsequently assessed photosynthetic capacity, starch storage, and stem hydraulics in four grapevine genotypes (two PD-resistant and two PD-susceptible), comparing those physiological changes to control plants. PD-susceptible genotypes showed a coordinated decline in photosynthesis, starch storage, and stem hydraulics, whereas Xf-inoculation led to no change in starch and stem hydraulics in the PD-resistant genotypes. Together these data support the idea of a link between loss of hydraulic conductivity due to tylosis production with a downstream photosynthetic decline and starch depletion in the PD-susceptible genotypes. Our data support the theory that hydraulic failure and carbon starvation underlie plant mortality resulting from PD.