Important Grapevine Diseases Research Articles

Grapevine Trunk Diseases in British Columbia: Incidence and Characterization of the Fungal Pathogens Associated with Esca and Petri Diseases of Grapevine.

Esca and Petri disease are two economically important grapevine diseases worldwide. This study reports for the first time the occurrence of both diseases on grapevines in British Columbia (BC) and subsequently in Canada. Visual assessment of 55,699 vines in 118 vineyards revealed a low incidence of esca with only 104 (0.2%) vines showing foliar symptoms. Young vine decline (YVD) was observed in 1,910 (7.8%) of 24,487 monitored young vines and in 52 (8%) of 654 young vines used as re-plants in mature vineyards. In 8 of 51 monitored young vineyards, YVD-affected vines ranged between 15 and 55%. Morphological studies along with DNA analyses of the ITS1-5.8S-ITS2, and part of the β-tubulin, actin, and translation elongation factor 1-α gene regions, allowed us to identify Cadophora luteoolivacea, Phaeomoniella chlamydospora, Phaeoacremonium iranianum, Togninia fraxinopennsylvanica, Togninia minima, and the novel species Phaeoacremonium canadense and Phaeoacremonium roseum from esca and Petri disease infected vines in BC. This study includes for the first time the EF1-α DNA marker in Phaeoacremonium spp. delineation. Pathogenicity studies showed all seven fungi to cause vascular symptoms similar to those observed in esca and Petri disease infected vines. Additionally, the "tiger-stripes" foliar symptom of esca was successfully reproduced when healthy potted vines were inoculated with BC isolates of Pa. chlamydospora, Pm. canadense, Pm. iranianum, T. fraxinopennsylvanica, and T. minima.

Effect of High Temperature and Exposure Time on Erysiphe necator Growth and Reproduction: Revisions to the UC Davis Powdery Mildew Risk Index.

Epidemics of powdery mildew, the most important disease of grapevines in California, are driven by moderate temperatures (21 to 30°C). High temperatures can delay or stop the growth and sporulation of Erysiphe necator. Using controlled conditions, we investigated the response of the pathogen's colony growth, conidiospore production, and germination to eight temperatures (30 to 44°C) at 12 exposure times (0.25 to 24 h). The pathogen survived, grew, and reproduced at higher temperatures than previously reported; exposure time was as important as temperature in defining lethal and sublethal effects. Lethal effects started at 36 to 38°C. Lethal exposure times decreased with increasing temperature. Based on this new information on the pathogen's biology, we tested revisions to the high-temperature threshold of the UC Davis Powdery Mildew Risk Index in field settings. No differences in the total number of fungicide applications resulted from the use of either the original or the revised models. However, use of the 38°C for 2 h threshold consistently showed equal (leaves) or better (fruit) disease control compared with the original model, as well as equal disease control compared with a calendar schedule, but with five fewer applications over the 2 years of the study.

Rapid detection of Grapevine leafroll-associated virus type 3 using a reverse transcription loop-mediated amplification method

Grapevine leafroll disease (GLD) is the most important disease of Grapevines in South Africa. Grapevine leafroll-associated virus type 3 (GLRaV-3) has a close association with the disease and is prevalent in South African vineyards. GLD can be controlled using a combination of virus-free planting material, systemic insecticides to control vector populations and removal of infected vines by roguing. Infected vines are identified each autumn using either symptom display (in red cultivars) or ELISA (in white cultivars). While ELISA is a simple, reliable means of testing for GLRaV-3, it is time consuming, laborious and insensitive and a quicker, more sensitive method of detecting GLRaV-3 in the field is needed. A single-tube one-step reverse transcription (RT) loop-mediated isothermal amplification (LAMP) assay combined with a simple RNA extraction protocol was developed for the rapid and easy detection of GLRaV-3. Hydroxy napthol blue was included as an indicator and under isothermal conditions at 60°C the target viral gene could be amplified in under 2h and positive results could be easily seen by examining the colour change from violet to sky blue. Using this method, 50 samples could be also pooled together with a single positive sample still being detected. A direct comparison of ELISA, nested PCR and RT-LAMP showed that RT-LAMP is as sensitive as nested PCR and could be performed in a much shorter time with less equipment. This assay is may be a possible alternative to ELISA for the detection of GLRaV-3 in the field.

Grapevine rootstock effects on scion sap phenolic levels, resistance to Xylella fastidiosa infection, and progression of Pierce's disease.

The xylem-limited bacterium Xylella fastidiosa (Xf) causes Pierce's disease (PD), an important disease of grapevine, Vitis vinifera L. Grapevine rootstocks were developed to provide increased resistance to root disease, but rootstock effects on cane and vine diseases remain unclear. Grapevines that consisted of Cabernet Sauvignon or Chardonnay grafted to 13 different rootstocks were inoculated with Xf and evaluated for PD severity and Xf titer after 6 months. A subset of six rootstock/scion combinations had xylem sap phenolic levels assessed in non-infected and Xf-infected grapevines. Vigor also was analyzed by measuring root lengths and masses. Cabernet Sauvignon grafted to 101-14MG, 1103P, 420A, or Schwarzmann had reduced PD severity compared to Cabernet Sauvignon grafted to 110R, 5BB, or SO4. Chardonnay grafted to Salt Creek or Freedom had reduced PD severity compared to Chardonnay grafted to RS3 or Schwarzmann. Chardonnay grafted to RS3 had greater Xf titer than Chardonnay grafted to 101-14MG, Freedom, or Salt Creek. No other differences in Xf titer among rootstocks were observed. Of the six scion/rootstock combinations which had xylem sap phenolics analyzed, Chardonnay/RS3 had the highest levels of most phenolics whereas Cabernet Sauvignon/101-14MG had the lowest phenolic levels. However, Chardonnay/101-14MG, which had mild PD symptoms, had greater sap levels of caftaric acid than other scion/rootstock combinations. Sap levels of caftaric acid, methyl salicylate, a procyanidin trimer, and quinic acid were greater in Xf-infected vs. non-infected grapevines. Chardonnay on 101-14MG or Salt Creek had greater root mass than Chardonnay on RS3. Cabernet Sauvignon on 101-14MG had greater root mass than Cabernet Sauvignon on 110R. These results identified rootstocks with the capacity for reducing PD symptom progression. Rootstocks also were shown to affect Xf titer, xylem sap phenolic levels, and plant vigor.

Virulence and cross-infection potential of Ilyonectria spp. to grapevine.

Black foot is an important disease of grapevines, affecting vines in nurseries as well as in young plantations. In recent years the disease has increased in incidence and severity throughout the world. Black foot is associated with at least two Campylocarpon and 12 Ilyonectria species, most of which have only recently been described. The recognition of previously unknown species, together with published reports of variability in virulence between and within species identified as I. macrodidyma and I. liriodendri , underlined the need to compare the virulence of isolates from these complexes. A further objective of this work was to determine the cross-infection potential of isolates of these species from other hosts to grapevine. Results from this study revealed recently described species such as I. lusitanica , I. estremocensis and I. europaea to be more virulent to grapevine than the species previously accepted as the main causal agents of black foot, such as I. liriodendri and I. macrodidyma . Furthermore, these results also provided support for isolates obtained from non-grapevine hosts to be as virulent to grapevines as isolates obtained from grapevine, underlying the cross-infection potential of these pathogens.

Prevalence of isolates of Botrytis cinerea resistant to multiple fungicides in Chilean vineyards

Gray mold (Botrytis cinerea) is an important disease of grapevines (Vitis vinifera) and requires several fungicide treatments to achieve a satisfactory control in Chile. Furthermore, a high resistance risk has developed because of the extensive use of specific fungicides with a single-site mode of action. The aim of this study was to determine the presence of resistance to the multiple fungicides currently used against B. cinerea in Chile. During 2007–2009 and 2011, 214 isolates of B. cinerea from 36 commercial vineyards were examined for sensitivity to anilinopyrimidines (cyprodinil or pyrimethanil), demethylation inhibitors (DMIs) (tebuconazole), hydroxyanilides (fenhexamid) and phenylpyrroles (fludioxonil). Of all of the isolates, 62.7% were resistant to anilinopyrimidines, 7.2% to DMIs, 27.1% to hydoxyanilides and 44.8% to phenylpyrrole derivates. Overall, 16 (12.3%) of the isolates were sensitive; although none was resistant to all four of the fungicide classes, and 50 (38.5%), 51 (39.2%), and 13 (10.0%) isolates were resistant to one, two and three fungicides, respectively. In vitro, resistant isolates were capable of causing fruit rot on wounded apples pretreated with any one of the five fungicides at label concentrations. To the best of our knowledge, this is the first report of isolates having simultaneous resistance to anilinopyrimidines, DMIs, phenylpyrroles and hydroxyanilides in B. cinerea populations from grapevines in Chile. Therefore, fungicide resistance is a serious problem that questions the sustainability of the current gray mold control strategy, which relies almost exclusively on fungicides with single-site modes of action.

The Perfect Stage of Powdery Mildew of Grapevine Caused by Erysiphe necator Found in Peru.

Grapevine (Vitis vinifera L.) has been cultivated in Peru since the sixteenth century to produce wine and grape brandy called "Pisco". Grapevine powdery mildew caused by Erysiphe necator (Schwein.) (formerly Uncinula necator [Schw.] Burr.; anamorph Oidium tuckeri) is currently the most important disease of grapevine in Peru. Table grape producers rely heavily on fungicide applications to manage powdery mildew infections. In Peru, the pathogen is normally found in the anamorphic state, except for one report of the teleomorphic state in 1972 (2) on wine grape varieties. In July 2011, ascomata were observed on table grapevine leaves cv. Sugraone in a commercial field near Huaral in the central coast of Peru. Abundant, mature (black) and immature (brown), globose ascocarps were visible on the abaxial leaf surfaces covered by the anamorphic state of the fungus. The chasmothecia were epiphyllous and ranged from 93.3 to 157.5 μm in diameter. The appendages were hyaline, variable in number (9 to 17), septate, with the apex helicoid when mature, and measuring 310 to 480 μm long. Each ascocarp contained four to seven subglobose asci (55.3 to 76.7 × 36.3 to 52.0 μm) with two to six (mostly three) ascospores. The ascospores were elliptical, hyaline, and measured 20.2 to 25.0 μm long by 11.1 to 17.3 μm wide. The pathogen was identified as E. necator on the basis of the host genus and morphology of the teleomorph (1). The teleomorphic state of E. necator could be a source of primary inoculum before infection by anamorphic conidia occurs, provide the basis for genetic recombination, and lead to more frequent appearance of new races. This could have serious implications for managing fungicide resistance in the pathogen population and may also result in the development of virulence to the resistance of some grape varieties tolerant to powdery mildew infections. In South America, the teleomorph of E. necator has been recently detected in Chile (3), and has caused great concern among grape producers. To our knowledge, this finding represents a first record of the presence of the ascigenous state of the pathogen on table grapes in Peru.

Multi-gene analysis and morphology reveal novel Ilyonectria species associated with black foot disease of grapevines

Black foot is an important disease of grapevines, which has in recent years been recorded with increased incidence and severity throughout the world, affecting grapevines both in nurseries and young vineyards. In the past the disease has been associated with infections by Ilyonectria macrodidyma, Ilyonectria liriodendri, Campylocarpon fasciculare, and Campylocarpon pseudofasciculare. Based on published data, a high level of genetic diversity was detected among isolates of I. macrodidyma. To resolve this issue, we employed a multigene analysis strategy (based on the β-tubulin, histone H3, translation elongation factor 1-α, and the internal transcribed spacers on both sides of the 5.8S nuclear ribosomal RNA gene) along with morphological characterisation to study a collection of 81 I. macrodidyma-like isolates from grapevine and other hosts. Morphological characters (particularly conidial size) and molecular data (highest resolution achieved with histone H3 nucleotide sequence) enabled the distinction of six monophyletic species within the I. macrodidyma complex, four of which (Ilyonectria alcacerensis, Ilyonectria estremocensis, Ilyonectria novozelandica, and Ilyonectria torresensis) are described here. This work forms part of an effort by the International Council on Grapevine Trunk Diseases to resolve the species associated with black foot disease, which we believe will clarify their taxonomy, and therefore help researchers to devise control strategies to reduce the devastating impact of this disease.

Physiological responses of elite barley ( Hordeum vulgare L.) cultivars to salt stress at germination stage

Grapevine leafroll disease (GLD) is the most important disease of Grapevines in South Africa. Grapevine leafroll-associated virus type 3 (GLRaV-3) has a close association with the disease and is prevalent in South African vineyards. GLD can be controlled using a combination of virus-free planting material, systemic insecticides to control vector populations and removal of infected vines by roguing. Infected vines are identified each autumn using either symptom display (in red cultivars) or ELISA (in white cultivars). While ELISA is a simple, reliable means of testing for GLRaV-3, it is time consuming, laborious and insensitive and a quicker, more sensitive method of detecting GLRaV-3 in the field is needed. A single-tube one-step reverse transcription (RT) loop-mediated isothermal amplification (LAMP) assay combined with a simple RNA extraction protocol was developed for the rapid and easy detection of GLRaV-3. Hydroxy napthol blue was included as an indicator and under isothermal conditions at 60 °C the target viral gene could be amplified in under 2 h and positive results could be easily seen by examining the colour change from violet to sky blue. Using this method, 50 samples could be also pooled together with a single positive sample still being detected. A direct comparison of ELISA, nested PCR and RT-LAMP showed that RT-LAMP is as sensitive as nested PCR and could be performed in a much shorter time with less equipment. This assay is may be a possible alternative to ELISA for the detection of GLRaV-3 in the field.

Spatial variation in response to ‘reduced input’ spray programs for powdery mildew and botrytis identified through whole-of-block experimentation

Background and Aims: Previous work has highlighted the utility of the whole-of-block approach to viticultural experimentation. Here, we use this approach as a means of evaluating alternative spray programs for managing two economically important grapevine diseases at commercial scale. Methods and Results: Two experiments were conducted in vineyards in the Coal River and Rokeby districts of Tasmania. The first, carried out in a 4.5 ha vineyard planted to Vitis vinifera L. cv. Pinot Noir, sought to evaluate fungicide programs for control of powdery mildew ( Erysiphe necator ), in particular with a view to reducing the amount of sulphur applied in organic production systems. The second sought to evaluate the benefit (if any) of changing the time of fungicide application from flowering to pre-bunch closure for the control of botrytis bunch rot ( Botrytis cinerea ) in a 2.4 ha Chardonnay vineyard. In both cases, treatments were applied to a whole-of-block experimental design using commercial spray equipment. Disease severity and the response to the various spray treatments, was spatially variable and related to topographic variation. Botrytis severity was also related to vine vigour. The powdery mildew results supported the retention of sulphur in organic spray programs, while Switch® (Syngenta Group, Basel, Switzerland) applied at pre-bunch closure in the botrytis experiment reduced disease severity relative to the application at flowering. Spatial variation in the response to the latter treatment, when examined four times pre-harvest, suggested that secondary spread may not have been an important mechanism for increasing disease severity over time. Conclusions: Consistent with the other work described in this series of papers, we conclude that the whole-of-block experimental approach offers both researchers and vineyard managers a means of acquiring more useful information than would be obtained from a conventional plot-based approach. Significance of the Study: This study highlights the value of collecting spatially distributed data as a means of better understanding the incidence, spread, progression and control of fungal grapevine diseases. As such, it provides a new application for this experimental approach, which enables spatial variability to be used as an experimental tool.

Using Marker-Assisted Selection to Breed Pierce’s Disease-Resistant Grapes

Pierce’s disease (PD), caused by the bacterium <i>Xylella fastidiosa,</i> is an important disease of grapevines in California, across the southern United States, and into South America. In regions where disease pressure is high, the cultivation of <i>Vitis vinifera</i> cultivars is difficult or impossible. This study reports on the introgression of PD resistance into elite wine, table, and raisin grape genetic backgrounds and on the reliability of PCR-based marker-assisted selection (MAS) to accelerate the breeding of PD-resistant grapes. This work documents the introgression of PD resistance from a homozygous resistant form of <i>V. arizonica,</i> b43-17. A total of 4,321 seedlings from 83 different crosses of resistant selections and high-quality <i>V. vinifera</i> cultivars from the F1 and first and second modified backcross generations (mBC1 and mBC2) were screened with two to three flanking microsatellite markers (VVIP26, ctg1026876 and VMC2a5) in the early spring 2006 and 2007. The alleles linked to resistance were unique in size and were not shared by susceptible <i>V. vinifera</i> selections. Based on the presence of unique resistant alleles, 1,683 seedlings from wine, table, and raisin grape background were selected. The distinctiveness of these resistant alleles allows the use of MAS to optimize the breeding of PD-resistant grape cultivars.

Invasion biology and host specificity of the grapevine yellows disease vector Hyalesthes obsoletus in Europe

AbstractWithin the past 10 years, the yellows disease ‘bois noir’ (BN) has become one of the commercially most important diseases of grapevine [Vitis vinifera L. (Vitaceae)] in Europe. Infection pressure is caused by phytoplasmas of the stolbur 16SrXII‐A group that are transmitted by a planthopper vector, Hyalesthes obsoletus Signoret (Homoptera: Auchenorrhyncha). Infestation happens as an accidental side‐effect of the feeding behaviour of the vector, as vector and pathogen proliferation is dependent on other plants. In Germany, the increase of BN is correlated with the use of a new host plant by the vector, increase in abundance of the vector on the new host plant, and dissemination of host plant‐specific pathogen strains. In this article, we investigate geographic and host‐associated range expansion of the vector. We test whether host‐plant utilization in Germany, hence the increase in BN, is related to genetic host races of the vector and, if so, whether these have evolved locally or have immigrated from southern populations that traditionally use the new host plant. The genetic population analysis demonstrates a recent expansion and circum‐alpine invasion of H. obsoletus into German and northern French wine‐growing regions, which coincides with the emergence of BN. No H. obsoletus mitochondrial DNA haplotype host‐plant affiliation was found, implying that the ability to use alternative host plants is genetically intrinsic to H. obsoletus. However, subtle yet significant random amplified polymorphic DNA (RAPD) genetic differentiation was found among host plant populations. When combined, these results suggest that a geographic range expansion of H. obsoletus only partly explains the increase of BN, and that interactions with host plants also occur. Further possible beneficial factors to H. obsoletus, such as temperature increase and phytoplasma interactions, are discussed.

Genetic variability and population structure of Grapevine virus A coat protein gene from naturally infected Italian vines

Grapevine virus A (GVA) is considered one of the viruses associated with rugose wood (RW), one of the most economically important diseases of grapevine. Thirty-seven GVA isolates collected from grapevine cultivars from Marche (central-eastern Italy), Apulia and Campania (southern Italy), were subjected to molecular characterization. The genetic and population diversity was studied in the coat protein (CP) gene by RT-PCR-RFLP analysis with three restriction enzymes (MseI, AluI, and AciI), and nucleotide sequencing. A new primer pair (CP1F/R) allowing amplification of the whole CP gene (621 bp) was developed. RFLP with AciI yielded the highest number of variants in GVA isolates, showing seven different ‘simple’ profiles (A, B, C, D, E, F, and G). ‘Complex’ profiles were also found, and the most common variant combination was A + B in 39% of isolates. The analysis of GVA sequences confirmed the presence of plants infected with more than one GVA variant and suggested that RT-PCR-RFLP is suitable for evaluating population diversity of GVA enabling a screening of different haplotypes. The distribution of RFLP profiles and the phylogenetic analysis were not correlated with the location of infected plants, showing the presence of a GVA population with genetic diversity in the average with those of RNA viruses.

Management of understorey to reduce the primary inoculum of Botrytis cinerea: Enhancing ecosystem services in vineyards

Botrytis bunch rot, caused by Botrytis cinerea (Pers.: Fr) is an important disease of grapevines that causes worldwide crop losses and reductions in wine quality. The pathogen predominantly overwinters on vine debris on the vineyard floor. In the current work, organic mulches were used to enhance biological degradation of vine debris to reduce levels of B. cinerea primary inoculum the following season. Four mulch types (anaerobically and aerobically fermented marc (grape pressings), inter-row grass clippings, and shredded office paper) were applied under 10-year-old Riesling vines in a 10-replicate randomized block design in New Zealand over two consecutive years. Plastic mesh bags, each containing naturally infected vine debris, were placed under vines on bare ground (control) and at the soil-mulch interface, in winter (July) 2003 and 2004. In each year, half the bags were recovered at flowering (December) and the remainder at leaf plucking (February), for assessment of B. cinerea sporulation from the vine debris and debris degradation rate. Bait lamina probes, which measure soil biological activity, were placed in the soil-mulch interface three weeks before each of the two bag-recovery dates in both years and were then removed and assessed at the same times as were the bags. All mulches led to a reduction in B. cinerea sporulation. This reduction was significantly correlated with elevated rates of vine debris decomposition and increased soil biological activity. Over both years, compared with the controls, all treatments gave a 3- to 20-fold reduction in B. cinerea sporulation, a 1.6- to 2.6-fold increase in vine debris degradation and in the two marc and the paper treatments, a 1.8- to 4-fold increase in activity of soil organisms. These results show the potential of enhanced soil organism activity in the soil for disrupting the B. cinerea life cycle. The implications of these results for infection levels of grapes are currently being investigated.

Development of a High-Throughput Method for Quantification of Plasmopara viticola DNA in Grapevine Leaves by Means of Quantitative Real-Time Polymerase Chain Reaction

ABSTRACT Plasmopara viticola is a strictly biotrophic oomycete that causes downy mildew, which is one of the most important grapevine diseases. Control of the disease is most often achieved by fungicide applications, which may have severe environmental consequences. Therefore, alternative control strategies based on biocontrol agents (BCAs) are currently in development. Thousands of potential BCAs have to be screened for their antagonist efficacy against Plasmopara viticola. Evaluation of their effect on the pathogen can be achieved by detecting the amount of P. viticola DNA in leaves treated with potential antagonists and infected with the pathogen. In this study, a rapid high-throughput method was developed for relative quantification of P. viticola DNA directly from Vitis vinifera leaves by means of multiplex real-time quantitative polymerase chain reaction (PCR) with TaqMan chemistry. This method allows simultaneous amplification, but independent detection, of pathogen and host DNA by using species-specific primers and TaqMan probes that are labeled with different fluorescent dyes. Including detection of V. vinifera DNA in the tests is fundamental because it provides an endogenous reference and allows normalization for variations caused by sample-to-sample differences in DNA extraction, PCR efficiencies, and pipetting volumes. The developed method allows highly sensitive and specific detection of P. viticola DNA (minimal detectable quantity of 0.1 pg). Moreover, high precision and reproducibility of TaqMan assays were observed over a linear range of four orders of magnitude, confirming the reliability of the developed PCR assay. Potential applications range from screening for BCA efficiency to evaluation of fungicide efficacy, or assessment of host resistance.

Powdery mildew and wine quality

Powdery mildew, caused by the fungus Uncinula necator, is a widespread and economically important disease of grapevines. The fungus grows superficially on green tissues of grapevines and other members of the Vitaceae. Powdery mildew costs the Australian grape and wine industry approximately A$30 million per year in terms of lost yield, reduced quality and disease management.

Epidemiology of grapevine anthracnose, caused byElsinoe ampelina

Abstract Anthracnose, caused by Elsinoe ampelina Shear, is an important disease of grapevines in the Auckland district. Young leaves, stems, and berries are susceptible to infection. Fully expanded leaves, and stem internodes bearing them, are highly resistant or immune. Berries become highly resistant, though not immune, about ‘50 days after anthesis, when soluble solids have risen above 5-7% in the juice. Wetness periods necessary for infection range from 7-10 hr at 12°c, in spring, down to 3-4 hr at 21°c, in summer. Conidia are produced in abundance 14 days later at 12°c, and, after 5 days, at 21°c. Spore flights of up to 7 m, in wind-borne rain-splash drops, were detected. Conidia from overwintered cane lesions initiate the epidemic after budburst in September. After flowering, in late November-early December, infection spreads to young berries and bunch stalks. In Auckland from October to March there are on average three or four separate rainy spells each month, each providing E. ampelina with at lea...