Identification and Spread of Fomitiporia punctata Associated with Wood Decay of Grapevine Showing Symptoms of Esca

Role of Rain in the Spore Dispersal of Fungal Pathogens Associated with Grapevine Trunk Diseases

Grapevine trunk diseases are caused by a complex of fungi that belong to different taxa, which produce different spore types and have different spore dispersal mechanisms. It is commonly accepted that rainfall plays a key role in spore dispersal, but there is conflicting information in the literature on the relationship between rain and spore trapping in aerobiology studies. We conducted a systematic literature review, extracted quantitative data from published papers, and used the pooled data for Bayesian analysis of the effect of rain on spore trapping. We selected 17 papers covering 95 studies and 8,778 trapping periods, concerning a total of 26 fungal taxa causing Botryosphaeria dieback (BD), Esca complex (EC), and Eutypa dieback (ED). Results confirmed the role of rain in the spore dispersal of these fungi but revealed differences among the different fungi. Rain was a good predictor of spore trapping for ED (AUROC = 0.820) and BD (0.766) but not for the ascomycetes involved in EC (0.569) and not for the only basidiomycetes, Fomitiporella viticola, studied as for spore discharge (AUROC not significant). Prediction of spore trapping was more accurate for negative prognosis than for positive prognosis; a rain cutoff of ≥0.2 mm provided an overall accuracy of ≥0.61 for correct prognoses. Spores trapped in rainless periods accounted for only <10% of the total spores. Our analysis had some drawbacks, which were mainly caused by knowledge gaps and limited data availability; these drawbacks are discussed to facilitate further research.

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.

Investigating Wood Decaying Fungi Diversity in Central Siberia, Russia Using ITS Sequence Analysis and Interaction with Host Trees

Wood-decay fungi (WDF) play a significant role in recycling nutrients, using enzymatic and mechanical processes to degrade wood. Designated as a biodiversity hot spot, Central Siberia is a geographically important region for understanding the spatial distribution and the evolutionary processes shaping biodiversity. There have been several studies of WDF diversity in Central Siberia, but identification of species was based on morphological characteristics, lacking detailed descriptions and molecular data. Thus, the aim of this study was to identify WDF in Central Siberia, regarding the degradation of host trees based on both morphological and molecular analyses. We collected 106 WDF samples from Krasnoyarsk and the Republic of Khakassia in 2014 and 2017, and identified a total of 52 fungal species from six main host tree genera. In order to assess the host preference of the WDF, we examined previous literature, and data from this study. We confirmed a division in host preference of WDF between gymnosperms and angiosperms. DNA-based identification and host preference assessment of the WDF provide preliminary data on WDF diversity and their role in nutrient cycles in the ecosystem of Central Siberia. To fully understand WDF diversity in Central Siberia, continuous long-term surveys, including DNA sequence data, are needed.

Spatial and Temporal Pattern Analyses of Esca Grapevine Disease in Vineyards in France

To assess the capacity of esca to spread within vineyards of the Bordeaux region, over 8 years of annual records, containing between 1,200 and 2,300 contiguous Cabernet Sauvignon vines from 15 mature vineyards, were used for spatial statistical analyses. A group of nonparametric tests, based on join count statistics and on permutation methods, was developed to characterize the spatial structure of esca-symptomatic vines in terms of spread in any direction or within-row only. Among vineyards, a large range of spatial patterns, from random to strongly structured, associated with various prevalence rates that increased over time were observed. In four vineyards, the complex esca distribution pattern indicated different levels of clustering. By contrast, in other vineyards, only small clusters of two adjacent symptomatic vines were observed, and they were localized along rows, without enlargement over time, except in one vineyard. An analysis of spatial dependence between previously and newly symptomatic vines within k-order neighborhoods (k = 1 to 5), showed, for 5 of the 15 vineyards, that the newly symptomatic vines were located close to previously infected vines, without a favored orientation or neighbor order. All the results together suggested a limited potential for secondary local spread from neighboring symptomatic vines.

Infection Caused by Phaeomoniella chlamydospora Associated with Esca-like Symptoms in Grapevine in Chile

Trunk diseases such as esca have been recognized as an economically important problem of grapevine worldwide. A study was conducted to characterize the distribution of Phaeomoniella chlamydospora in Chile. A field survey of young and mature grapevines from 67 vineyards located along a 1,315-km north-south axis demonstrated that P. chlamydospora was present in 94.9% of the grapevine samples showing the black-wood streaking symptom (BWS) but not the characteristic foliar symptoms of esca. Phylogenetic analysis of the ribosomal DNA internal transcribed spacer (ITS) combined with β-tubulin (BT) genes grouped Chilean isolates together with reference isolates from South Africa and the United States, whereas Spanish isolates were clustered separately. Chilean isolates differed by only 2 to 3 bp for BT and ITS, respectively. Conidia germinated at 5 to 35°C, with an optimal temperature of 25 to 30°C. Isolates were pathogenic, and Koch's postulates were fulfilled in separate sets of inoculations of axenic plantlets, cuttings, 2-year-old plants, spurs, and shoots of V. vinifera. This study showed that P. chlamydospora was associated consistently with BWS and no other apparent symptom in young and mature grapevines, including nursery plants, in Chile. Inoculum was absent from the soil, grapevine pruning debris, sap samples, and herbaceous weeds, which is in contrast to past studies. At this time, Vitis spp. are the only known hosts of P. chlamydospora in Chile.

Species recognition, geographic distribution and host-pathogen relationships: a case study in a group of lignicolous basidiomycetes, Phellinus s.l

Morphological, phylogenetic (sequencing of the ribosomal ITS region) and, if applicable, biological (pairings of single-spore testers) species recognition have been used to resolve relationships among 69 collections belonging to the Hymenochaetales genera Phellinus s.str. and Fomitiporia. The isolates originate from a variety of host plants in Europe, North America and Asia. Separate application of recognition modes led to differing results concerning the number of species, geographic distribution and host range. Sole application of morphological criteria was of limited value, especially in taxa exhibiting a wide distribution, both in terms of geographic origin and ecological niche. Relationships of putatively con-specific collections originating from different continents preferably should be resolved by using an integrative approach. In this study, application of a strict morphological approach led to the recognition of seven species. When using molecular and pairing test data, at least 12 species were detectable. Two of them, F. hesleri and F. polymorpha, are described as new. The number of Phellinus s.str. and Fomitiporia species supposed to have Northern Hemispheric or cosmopolitan distribution, when morphological characters are applied for species recognition, has been reduced significantly. As firm tendencies within morphological species, genetic divergence was more distinct in uniparental than in biparental taxa. In the latter, a strong correlation was observed between phylogenetic and biological species recognition. Overall length of the ribosomal ITS region clearly separated Phellinus s.str. and Fomitiporia but was of limited value as a diagnostic tool at species level. The level of innerspecific morphological plasticity of fruit bodies differs widely between even closely related species, suggesting that morphological transitions occur quite frequently in this fungal group. Considerable instability of the reproduction mode was evident in strains belonging to Phellinus tremulae and among closely related species of Fomitiporia.

Leaf stripe form of esca induces alteration of photosynthesis and defence reactions in presymptomatic leaves

Esca is a destructive disease in grapevines (Vitis vinifera L.) caused by at least three fungi and characterised by two different external symptoms, the apoplectic and leaf stripe form. This latter form can be discerned as soon as symptoms become visible, but the preceding discrete signs during incubation are poorly or not understood. To further understand the development of the leaf stripe form, the period preceding and following the appearance of symptoms was investigated by studying physiological and molecular markers associated with photosynthetic mechanisms and stress response. No perturbation of any targeted metabolism was observed in asymptomatic leaves of asymptomatic canes from vines showing the leaf stripe form of esca. Conversely, drastic alterations of photosynthesis functions were registered in presymptomatic leaves, as revealed by the decrease of gas exchange and chlorophyll fluorescence, and the repression of photosynthesis-related genes. These alterations were amplified during symptom development. Expression of defence-related genes was affected and detected early in presymptomatic leaves and amplified during symptom expression. Our results suggest that grapevines may react precociously by reducing photosynthesis and triggering defence mechanisms in response to the leaf stripe form of esca.

Early events prior to visual symptoms in the apoplectic form of grapevine esca disease

Plant infection by pathogens generates various forms of symptoms. Most of them have been described as soon as they become visible, whereas preceding, discrete signs during incubation are poorly or not understood. In Vitis vinifera, esca-related pathogenic fungi inhabit living trunk wood and induce the so-called apoplexy, a sudden wilting of leaves within a few days. To further understand the apoplexy expression, the period preceding symptom appearance was investigated by following physiological and molecular markers associated with photosynthetic mechanisms and stress responses. Within the week preceding symptoms, drastic physiological alterations of photosynthesis were registered in pre-apoplectic vines, as revealed by a decrease in gas exchange, changes in chlorophyll fluorescence, and repression of photosynthesis-related genes. In the meantime, expression of defense-related genes was induced and amplified during symptom expression. Water-stress-related genes were specifically investigated because water transport may be impeded by clogging xylem vessels due to esca-causing fungi. Neither of the tested water-stress-related genes was affected in pre-apoplectic grapevine leaves whereas these genes were downregulated in drying leaves. Our results suggest that, during incubation of esca apoplexy, grapevine perceives some signals (likely fungi-originated toxins) and reacts by reducing photosynthesis and triggering defense mechanisms.

[Esca and Black Dead Arm: two major actors of grapevine trunk diseases]

Grapevine trunk diseases are very harmful to wine-growing heritage durability because the fungi responsible, by attacking perennial organs, cause at a more or less long-term the death of the vine stock. Esca and BDA are the two main pathogens inducing such decaying diseases. The infection can be diagnosed by the presence in the wood forming tissues of sectorial and/or central necrosis, which revealed itself by brown stripes or canker, and at the foliar level by discoloration and withering. This review presents an overview of both Esca and BDA, their symptomatology, the characteristics of the associated fungi and host-pathogen interactions. To conclude, a progress report on the control of both diseases is discussed.

Alteration of photosynthesis in grapevines affected by esca

ABSTRACT To further understand the development of esca disease in grapevine, its physiological impact on plants grown in the vineyard was characterized, focusing mainly on photosynthesis. For this purpose, the state of the photosynthetic apparatus was evaluated in symptomatic and asymptomatic leaves in esca-infected grape plants, and wood carbohydrates stored in annual canes were assayed. In symptomatic leaves, esca greatly affected grapevine physiology. Foliar symptoms were associated with both stomatal closure and alteration of the photosynthetic apparatus as revealed by (i) a decrease in CO(2) assimilation, transpiration, and a significant increase in intercellular CO(2) concentration; (ii) a strong drop in both the maximum fluorescence yield and the effective Photosystem II quantum yield; and (iii) a reduction of total chlorophyll but a stable carotenoid content. On symptomatic canes, all these variables were affected more on leaves with symptoms than without symptoms, suggesting a gradation in photosynthesis disruptions in the plant according to the degree of symptom severity. In addition, canes of symptomatic plants had reduced carbohydrate reserves during the winter rest, whether they exhibit symptoms or not. The following year, the lower pool of reserves may contribute to a significant decrease in plant development, as well as a global loss in plant vigor.

Spatial and Genetic Analysis of a Flag Shoot Subpopulation of Erysiphe necator in Italy

ABSTRACT Erysiphe necator overwinters as ascospores in cleistothecia and mycelium in dormant buds of grapevines. Shoots developing from infected buds early in the growing season are covered with dense mycelium and are known as "flag shoots". Combining epidemiological and genetic analyses, the objective of this study was to analyze the spatial and genetic structure of a flag shoot subpopulation of E. necator as a way to assess the contribution of flag shoots as primary inoculum, and to determine if flag shoot subpopulations are clonal with only one mating type. One vineyard in Tuscany, Italy was surveyed intensively for flag shoots for 8 years; isolations of E. necator were made from flag shoots for 5 years. We observed distinct disease foci developing around flag shoots early in epidemics, demonstrating a steep dispersal gradient of conidia and the importance of flag shoots as primary inoculum sources. Flag shoots were spatially aggregated within and between years, most likely as a result of short-distance dispersal of conidia from flags early in the season when dormant buds for the next year's shoots are formed and are susceptible to infection. The two mating types were found in 1:1 ratios in this flag shoot subpopulation. Genotypic diversity, based on inter-simple sequence repeat markers, was high in all years with only two haplotypes occurring twice, and subpopulations were genetically differentiated between years. Similarities between haplotypes were not spatially autocorrelated. One multilocus analysis of population structure is consistent with the hypothesis of random mating but another is not. These results are not consistent with expectations for a strictly clonal or strictly randomly mating flag shoot subpopulation. Instead, the hypothesis that the flag shoot subpopulation of E. necator may reproduce clonally and sexually needs further testing.