Grapevine Trunk Diseases Research Articles

Phytotoxins produced by Didymella glomerata and Truncatella angustata, associated with grapevine trunk diseases (GTDs) in Iran

Didymella glomerata and Truncatella angustata associated with grapevine trunk diseases (GTDs) in Iran, were grown in vitro to evaluate the production of phytotoxic metabolites as potential pathogenicity determinants. 2,5-Dihydroxymethylfuran and (+)-6-hydroxyramulosin were isolated from the culture filtrates of D. glomerata and T. angustata, respectively. They were identified by physical and spectroscopic (essentially 1 D and 2 D 1H and 13C NMR and ESIMS) methods and X ray analysis. Both compounds induced significant necrosis and curling on the leaves of the host plant Vitis vinifera L. and the effects were concentration dependent. No effect was observed on the leaves of the non-host Solanum lycopersicum L.. plant.

Diversity of Botryosphaeriaceae causing grapevine trunk diseases and their spatial distribution under different climatic conditions in Algeria

Diversity of Botryosphaeriaceae causing grapevine trunk diseases and their spatial distribution under different climatic conditions in Algeria

White Rot Fungi (Hymenochaetales) and Esca of Grapevine: Insights from Recent Microbiome Studies.

Esca is a major grapevine trunk disease that heavily affects vineyards in the Northern hemisphere. The etiology and epidemiology of this disease have been subject of dispute ever since the earliest disease reports. The reason behind such debate is the presence of multiple internal and external symptoms, as well as several putative and confirmed wood pathogens. While the role of pathogenic fungi, as causal agents of wood symptoms, has been thoroughly assessed, their role in the expression of leaf symptoms remains to be fully elucidated. In this review, we analyzed etiological and epidemiological data, with a special focus on the microbiological aspect of esca and the involvement of Hymenochaetales (Basidiomycota). Vineyard studies have associated leaf symptoms with the presence of white rot, most frequently caused by Fomitiporia mediterranea (Hymenochaetales), while tracheomycotic fungi are commonly found, with similar abundance, in symptomatic and asymptomatic vines. Pathogenicity trials have excluded a direct effect of Hymenochaetales species in triggering leaf symptoms, while the data concerning the role of tracheomycotic fungi remains controversial. Recent microbiome studies confirmed that F. mediterranea is more abundant in leaf-symptomatic vines, and treatments that effectively control leaf symptoms, such as sodium arsenite spray and trunk surgery, act directly on the abundance of F. mediterranea or on the presence of white rot. This suggest that the simultaneous presence of Hymenochaetales and tracheomycotic fungi is a pre-requisite for leaf symptoms; however, the relation among fungal pathogens, grapevine and other biotic and abiotic factors needs further investigation.

Impact of temperature variation on the phytotoxic secondary metabolite production by Lasiodiplodia theobromae

AbstractBotryosphaeriaceae species are associated with grapevine trunk diseases. Lasiodiplodia theobromae plays a significant role as one of the most virulent grapevine pathogens in the world. In this study, we evaluate the effects of temperature on phytotoxin‐induced virulence in Lasiodiplodia theobromae. The fungal strain is grown in Czapek‐Dox liquid medium at four different temperatures (20°C, 25°C, 30°C and 35°C) for 14 days under dark conditions. The culture filtrates were screened for three selected phytotoxins, indole‐3‐carboxylic acid, jasmonic acid, and lasiodiplodin using UPLC MS/MS techniques. Phytotoxicity of the crude culture filtrates was tested on detached grapevine leaves. With UPLC MS/MS analysis, we identified that indole‐3‐carboxylic acid and jasmonic acid production varied with the increasing temperature, and did not detect any lasiodiplodin. At high temperatures, we observed a significant increase in the phytotoxicity of crude culture filtrates on the detached grapevine leaves. The most severe necrotic leaf lesions were observed when inoculated with crude culture filtrates extracted at 35°C.

Fungal pathogens associated with black foot of grapevine in China

Grapevine trunk diseases (GTDs) are the most destructive diseases in grape-growing regions worldwide. Black foot is one of the important GTDs affecting young vineyards and nurseries. This disease has not been reported in China. During 2017 and 2019, field surveys were carried out in the Guangxi, Hebei, Ningxia, Shanxi, and Xinjiang provinces of China. Incidence of plants with black foot symptoms was 0.1% to 1% in the surveyed vineyards. Plant samples with poorly developed shoots and canes, chlorotic leaves, and necrotic trunks or roots were collected from the five provinces. In total, 50 fungal isolates were obtained from symptomatic tissues. Based on morphological and multi-gene phylogenetic analyses, five species were identified as Cylindrocladiella lageniformis, Dactylonectria torresensis, D. macrodidyma, D. alcacerensis and Neonectria sp.1. Pathogenicity was assessed using young, healthy detached green shoots of grapevine ‘Summer Black’ and potted 3-month-old ‘Summer Black’ cuttings. Inoculated detached shoots developed necroses after 7 d, and inoculated cuttings after 80 d. Fungi were re-isolated from necrotic lesions. Among the five species, D. macrodidyma was the most aggressive. This is the first report of C. lageniformis, D. torresensis, D. macrodidyma, D. alcacerensis, and Neonectria sp. 1 associated with black foot in China. This study has enhanced knowledge of the fungi associated with black foot in China, and will assist development of control measures for this disease.

Characterization of Lasiodiplodia species associated with grapevines in Mexico

Botryosphaeria dieback is one of the most prevalent grapevine trunk diseases (GTDs), and is caused by fungi in the Botryosphaeriaceae. Fungi invade grapevine vascular systems mainly through pruning wounds, and cause cankers and necrotic lesions, which lead to grapevine decline and death. Lasiodiplodia theobromae has been reported as a highly virulent pathogen of grapevine, and was previously reported in Mexican vineyards. The taxonomy of Lasiodiplodia was recently revised, adding new species, and some were reduced to synonymy. This study aimed to characterize Lasio-diplodia producing grapevine dieback symptoms in Sonora and Baja California, Mexico. Using the phylogenetic markers tef1-α and ITS regions, Lasiodiplodia brasiliensis, L. crassispora, L. exigua, and L. gilanensis were identified. Lasidiplodia exigua was the most prevalent species. Lasiodiplodia brasiliensis and L. gilanensis were very virulent to ‘Cabernet Sauvignon’ plants, while L. exigua and L. gilanensis were less virulent, and L. crassispora did not produce lesions at 2 months post-inoculation. The optimum temperature of the Lasiodiplodia spp. was 28°C, but all four species grew up to 37°C, and the isolates of L. exigua grew slowly at 40°C. This is the first report of the four of Lasio-diplodia species in vineyards of Mexico.

Fomitiporia mediterranea M. Fisch., the historical Esca agent: a comprehensive review on the main grapevine wood rot agent in Europe

Fomitiporia mediterranea M. Fisch. (Fmed) is a basidiomycete first described in 2002, and was considered up to then as part of Fomitiporia punctata (P. Karst) Murrill. This fungus can degrade lignocellulosic biomass, causing white rot and leaving bleached fibrous host residues. In Europe Fmed is considered the main grapevine wood rot (Esca) agent within the Esca disease complex, which includes some of the most economically important Grapevine Trunk Diseases (GTDs). This review summarises and evaluates published research on Fmed, on white rot elimination by curettage or management by treatments with specific products applied to diseased grapevines, and on the relationship between wood symptoms and Grapevine Leaf Stripe Disease (GLSD) in the Esca disease complex. Information is also reviewed on the fungus biology, mechanisms of pathogenicity, and their possible relationships with external foliar symptoms of the Esca disease complex. Information on Fmed control strategies is also reviewed.

In planta Activity of the Novel Copper Product HA + Cu(II) Based on a Biocompatible Drug Delivery System on Vine Physiology and Trials for the Control of Botryosphaeria Dieback.

The growing concerns on human and environment health are forcing the plant protection industry toward the formulation of more eco-sustainable plant protection products (PPP), both efficient and innovative in their approach to disease control. A large number of these innovative formulations now rely on a combination of pathogens antagonistic properties and stimulation of natural plant defense to pathogens. The formulation HA + Cu(II), in which copper is delivered to the plants by the drug-delivery molecule hydroxyapatite (HA), was found efficient against the grapevine pathogens Plasmopara viticola and Phaeoacremonium minimum and able to induce the host-plant defense system. We investigated the HA + Cu(II) impacts on grapevine physiology, both in uninfected and when infected by the Botryosphaeria dieback agents Diplodia seriata and Neofusicoccum parvum. This study of plant physiology and disease impact were addressed to evaluate both the HA + Cu(II) potential as a plant defense elicitor and its possible and future use as PPP in vineyard. Our results showed that HA + Cu(II) induced several key-defense genes without negatively affecting plant growth and photosynthetic activity. In addition, fungistatic effect on the two Botryosphaeriaceae at the in planta tested concentrations is reported. Altogether, our results obtained under controlled conditions fully support the potential of HA + Cu(II) as a promising PPP toward grapevine trunk diseases in vineyard.

The Influence of Temperature on the Growth, Sporulation, Colonization, and Survival of Trichoderma spp. in Grapevine Pruning Wounds

Trichoderma is a genus of fungi used for the biological control of plant diseases and a large number of its bio-formulates are available in the market. However, its efficacy under field conditions remains unclear, especially for the protection of grapevine plants against Grapevine Trunk Diseases (GTDs). These diseases are caused by a complex of fungal pathogens whose main point of entrance into the affected plants is through pruning wounds. In this research, different Trichoderma native strains have been evaluated according to their ability to grow at different temperatures and their capacity to colonize pruning wounds in adverse climatic conditions. Strains from section Trichoderma have adapted to cooler conditions. On the other hand, strains from clade Harzianum/Virens grow at higher temperatures. However, differences can also be found between strains inside the same clade/section. Native strains were able to colonize more than 70% of vine pruning wounds in winter conditions. The Trichoderma strain T154 showed a significantly higher re-isolation degree from vine plants and its concentration was optimized for spraying onto vine plants. In conclusion, Trichoderma native strains are better adapted to survive in a changing environment, and they could give better protection to grapevine plants in co-evolution with each specific vineyard.

Detection of spores of causal fungi of dieback-type trunk diseases in young, asymptomatic vineyards and mature, symptomatic vineyards

Grapevine trunk diseases threaten grape production worldwide. In California, preventative practices (delayed pruning, fungicide applications after pruning) that reduce infections of pruning wounds by pathogen spores produced with rain are timed during the dormant season, when high spore-trap counts of the causal fungi are reported from studies in mature, symptomatic vineyards. Similar studies in young, asymptomatic vineyards are lacking. Given infrequent usage by California growers of preventative practices in young vineyards, empirical data on spore detection may provide convincing evidence to start preventing trunk diseases before symptoms appear. Active and passive spore traps were examined after rain from December to March for four years (2013–2017) in six young, asymptomatic (<5-years-old in year 1) and six mature, symptomatic (13–18-years-old in year 1) vineyards, in Lodi and Napa, California, USA wine-grape regions. We compared detection of spores of causal fungi of Botryosphaeria-, Eutypa-, and Phomopsis diebacks, which are common and widespread trunk diseases in California. From 769 samples, we isolated 15 species in culture, with DNA sequencing of 2 bar-coding loci for species-level identification. Detections (defined as presence of a species at least once per timepoint per site) were sparse in years 1 and 2, and so statistical analyses of detections pooled across timepoints and sites were restricted to years 3 and 4. Most common among all 12 sites and both trap types were Diplodia seriata and Diaporthe chamaeropis. Our novel species-level detections of six Diaporthe species fill a gap in the knowledge of which species can spread during California's dormant season. Overall, detections in young sites in years 3 and 4 (10 and 29 detections, respectively) were significantly lower than those of mature sites (31 and 57 detections, respectively). The presence of spores in young sites, even with no symptomatic vines, suggests preventative practices are needed in young vineyards. Nonetheless, our findings of more detections in mature sites reinforces higher usage by growers of preventative practices in mature, symptomatic vineyards.

Critical timing of fungicide application for pruning wound protection to control grapevine trunk diseases

Critical timing of fungicide application for pruning wound protection to control grapevine trunk diseases

The Influence of Water Deficit Stress on the Grapevine Trunk Disease Pathogens Eutypa lata and Diplodia seriata.

The increasing prevalence of the grapevine trunk diseases Eutypa and Botryosphaeria dieback has been attributed, in part, to abiotic stresses imposed on vineyards as production intensifies worldwide. The aim of this study was to evaluate the influence of water deficit irrigation practices on the infection of pruning wounds by Eutypa lata and Diplodia seriata and the subsequent rate of colonization. Two vineyard trials were conducted over two consecutive seasons in South Australia, one in the Riverland with 'Cabernet Sauvignon' with four irrigation treatments (100, 50, 25, and 12.5% of the standard irrigation program) and another in the Barossa Valley with 'Shiraz' on six rootstocks and own roots, either irrigated or not irrigated. According to leaf water potential assessments, vines with reduced irrigation were generally in water deficit and therefore subjected to stress. On the whole, incidence of wound infection and distance of colonization were similar between irrigation treatments for both pathogens, except in the Riverland, where E. lata colonized canes to a greater extent in well-watered vines than those in water deficit. Only vines on rootstock 'Ramsey' in the Barossa Valley had greater extent of colonization by E. lata in the nonirrigated vines. There was no correlation between internal staining and colonization, with both pathogens recovered to nearly 20 cm ahead of the staining. Water deficit did not increase the susceptibility of grapevine pruning wounds to infection or colonization of the subtending tissue by E. lata and D. seriata. In fact, there was evidence of lower susceptibility to colonization by E. lata in vines subjected to severe water deficit.

Bacteria associated with wood tissues of Esca‐diseased grapevines: functional diversity and synergy with Fomitiporia mediterranea to degrade wood components

SummaryFungi are considered to cause grapevine trunk diseases such as esca that result in wood degradation. For instance, the basidiomycete Fomitiporia mediterranea (Fmed) is overabundant in white rot, a key type of wood‐necrosis associated with esca. However, many bacteria colonize the grapevine wood too, including the white rot. In this study, we hypothesized that bacteria colonizing grapevine wood interact, possibly synergistically, with Fmed and enhance the fungal ability to degrade wood. We isolated 237 bacterial strains from esca‐affected grapevine wood. Most of them belonged to the families Xanthomonadaceae and Pseudomonadaceae. Some bacterial strains that degrade grapevine‐wood components such as cellulose and hemicellulose did not inhibit Fmed growth in vitro. We proved that the fungal ability to degrade wood can be strongly influenced by bacteria inhabiting the wood. This was shown with a cellulolytic and xylanolytic strain of the Paenibacillus genus, which displays synergistic interaction with Fmed by enhancing the degradation of wood structures. Genome analysis of this Paenibacillus strain revealed several gene clusters such as those involved in the expression of carbohydrate‐active enzymes, xylose utilization and vitamin metabolism. In addition, certain other genetic characteristics of the strain allow it to thrive as an endophyte in grapevine and influence the wood degradation by Fmed. This suggests that there might exist a synergistic interaction between the fungus Fmed and the bacterial strain mentioned above, enhancing grapevine wood degradation. Further step would be to point out its occurrence in mature grapevines to promote esca disease development.

Activity of Anthracenediones and Flavoring Phenols in Hydromethanolic Extracts of Rubia tinctorum against Grapevine Phytopathogenic Fungi.

In this work, the chemical composition of Rubia tinctorum root hydromethanolic extract was analyzed by GC–MS, and over 50 constituents were identified. The main phytochemicals were alizarin-related anthraquinones and flavoring phenol compounds. The antifungal activity of this extract, alone and in combination with chitosan oligomers (COS) or with stevioside, was evaluated against the pathogenic taxa Diplodia seriata, Dothiorella viticola and Neofusicoccum parvum, responsible for the so-called Botryosphaeria dieback of grapevine. In vitro mycelial growth inhibition tests showed remarkable activity for the pure extract, with EC50 and EC90 values as low as 66 and 88 μg·mL−1, respectively. Nonetheless, enhanced activity was attained upon the formation of conjugate complexes with COS or with stevioside, with synergy factors of up to 5.4 and 3.3, respectively, resulting in EC50 and EC90 values as low as 22 and 56 μg·mL−1, respectively. The conjugate with the best performance (COS-R. tinctorum extract) was then assayed ex situ on autoclaved grapevine wood against D. seriata, confirming its antifungal behavior on this plant material. Finally, the same conjugate was evaluated in greenhouse assays on grafted grapevine plants artificially inoculated with the three aforementioned fungal species, resulting in a significant reduction in the infection rate in all cases. This natural antifungal compound represents a promising alternative for developing sustainable control methods against grapevine trunk diseases.

Biscogniauxia rosacearum the charcoal canker agent as a pathogen associated with grapevine trunk diseases in Zagros region of Iran

Grapevine trunk diseases (GTDs) are well-known and significant fungal diseases of Vitis vinifera with a worldwide distribution. During August to November 2016 in a survey to characterize fungi associated with grapevine trunk diseases in Kermanshah Province (west of Iran) vineyards, 286 fungal isolates were obtained. Based on morphology and DNA sequences data eight species were identified, of which Biscogniauxia rosacearum, Neoscytalidium hyalinum and Phaeoacremonium minimum were the most aggressive fungal pathogenic species characterized in this research. N. hyalinum was the most prevalent species. N. hyalinum and Ph. minimum have previously been reported from Vitis vinifera. Thus far, there are two records of Biscogniauxia mediterranea and Biscogniauxia capnodes on grapevine in the world with no data on pathology aspects. To our knowledge, it is the first time B. rosacearum is reported from grapevine across the globe. Pathogenicity test with three strains of B. rosacearum on 2-year-old potted grapevines confirmed the pathogenicity of B. rosacearum on grapevine. The proximity of vineyards to the oak trees in Zagros forests as one of the plant hosts of Biscogniauxia spp. further highlights the need for extensive studies on B. rosacearum as a new fungal pathogen.

Application methods and modes of action of Pantoea agglomerans and Paenibacillus sp., to control the grapevine trunk disease-pathogen, Neofusicoccum parvum

Despite an increasing number of studies being carried out on the biocontrol of grapevine trunk diseases (GTDs), no commercial bacterial products have yet been developed to control GTDs. Knowledge of the precise modes of action (MOA) and the different application methods (AM) for biocontrol agents is crucial if they are to be successful in the field. In light of this, the present study aimed at selecting the most appropriate AM for eight bacterial strains with high potential for controlling Neofusicoccum parvum. These strains were applied on one-year-old grapevine in pots (grown from cuttings) using three methods: co-inoculation at stem level, preventive inoculation at stem level and preventive inoculation at the soil surface. The inhibitory activity of the bacterial strain against N. parvum was significantly dependent on the AM. Application of bacterial strains to stems, especially in a preventive way, was much more efficient than inoculation in the soil. When performing preventive inoculation on stems, the inhibition of N. parvumwood necrosis reached 50 and 65 % for Pantoea agglomerans (S1) and Paenibacillus sp. (S19) respectively. To decipher the underlying processes linked to fungal inhibition, the way in which several MOA affected the antagonistic capacity of these two strains was studied via in vitro and in planta assays. While P. agglomerans (S1) inhibited N. parvum by the secretion of antifungal volatile compounds, Paenibacillus sp. (S19) mainly inhibited this pathogen by antibiosis. In addition, both bacterial strains induced systemic defenses in grapevine. However, this affect tended to be higher at 15-dpi after inoculation with P. agglomerans (S1) than after innoculation with Paenibacillus sp. (S19) (three defense genes repressed versus five respectively). Finally, P. agglomerans (S1) and Paenibacillus sp. (S19) were shown to be potential biocontrol candidates for fighting N. parvum in grapevine, due to the combination of direct control via their antifungal activity and indirect control via their ability to activate the grapevine defense system.

Application methods and modes of action of &lt;i&gt;Pantoea agglomerans&lt;/i&gt; and &lt;i&gt;Paenibacillus&lt;/i&gt; sp. to control the grapevine trunk disease-pathogen, &lt;i&gt;Neofusicoccum parvum&lt;/i&gt;

Despite an increasing number of studies being carried out on the biocontrol of grapevine trunk diseases (GTDs), no commercial bacterial products have yet been developed to control GTDs. Knowledge of the precise modes of action (MOA) and the different application methods (AM) for biocontrol agents is crucial if they are to be successful in the field. In light of this, the present study aimed at selecting the most appropriate AM for eight bacterial strains with high potential for controlling Neofusicoccum parvum. These strains were applied on one-year-old grapevine in pots (grown from cuttings) using three methods: co-inoculation at stem level, preventive inoculation at stem level and preventive inoculation at the soil surface. The inhibitory activity of the bacterial strain against N. parvum was significantly dependent on the AM. Application of bacterial strains to stems, especially in a preventive way, was much more efficient than inoculation in the soil. When performing preventive inoculation on stems, the inhibition of N. parvumwood necrosis reached 50 and 65 % for Pantoea agglomerans (S1) and Paenibacillus sp. (S19) respectively. To decipher the underlying processes linked to fungal inhibition, the way in which several MOA affected the antagonistic capacity of these two strains was studied via in vitro and in planta assays. While P. agglomerans (S1) inhibited N. parvum by the secretion of antifungal volatile compounds, Paenibacillus sp. (S19) mainly inhibited this pathogen by antibiosis. In addition, both bacterial strains induced systemic defenses in grapevine. However, this affect tended to be higher at 15-dpi after inoculation with P. agglomerans (S1) than after innoculation with Paenibacillus sp. (S19) (three defense genes repressed versus five respectively). Finally, P. agglomerans (S1) and Paenibacillus sp. (S19) were shown to be potential biocontrol candidates for fighting N. parvum in grapevine, due to the combination of direct control via their antifungal activity and indirect control via their ability to activate the grapevine defense system.

Effect of Abamectin on Fungal Growth and Its Efficacy as a Miticide in the Laboratory

Abamectin was tested for use with solid agar media in the laboratory to eliminate or kill the common mold mite Tyrophagus spp. in fungal cultures of Phaeomoniella chlamydospora and Phaeoacremonium minimum, two important grape pathogens involved in grapevine trunk disease. Abamectin concentrations tested were at or below the recommended dosage for abamectin in greenhouse spray applications (≤625 µg/ml) to control mites and determine the following: (i) if fungal growth would be inhibited and (ii) if mites would be killed or their activity suppressed. Abamectin was either added to the media before autoclaving or filter-sterilized and added after autoclaving to test the effects of autoclaving on abamectin efficacy. Streptomycin (100 µg/ml) was also added to a set of treatments to determine whether this commonly used antibiotic would affect abamectin efficacy against mites or have an effect on fungal growth when combined with abamectin. Filter-sterilized abamectin in the range of 62.5 to 312 µg/ml, delivered to the media after autoclaving, provided the most effective control of mites while also showing limited inhibition of fungal growth on solid agar media in the absence of streptomycin. The addition of filter-sterilized streptomycin had no significant effect on fungal growth for Phaeomoniella chlamydospora, whereas for Phaeoacremonium minimum a small but significant reduction in growth with streptomycin occurred at abamectin concentrations >62.5 µg/ml.

Characterization of Grapevine Wood Microbiome Through a Metatranscriptomic Approach.

Grapevine trunk diseases threaten wine and table grape production worldwide, primarily by reducing yields and, in its advanced stages, causing plant death. Among those diseases, the complex etiology disease known as hoja de malvón (HDM) significantly concerns Argentinian and Uruguayan viticulture. At least four different fungi are associated with this disease, but their role and interactions with other wood microorganisms are understudied. In this sense, analyzing grapevine wood microbiome composition could help understand microbial interactions occurring in HDM onset. Hence, a metatranscriptomic study was performed for the microbiome characterization of mature field-grown Vitis vinifera cv. Malbec, leaf-symptomatic or leaf-asymptomatic. The microbiome was mainly represented by Dothideomycetes and Actinobacteria. In the plant with more marked symptoms, higher levels of the Basidiomycota Arambarria destruens and Phellinus laevigatus were detected. Despite this particular difference, discriminating symptomatic from asymptomatic plants based on the presence or abundance of HDM pathogens was not possible. Alpha diversity and rank-abundance curve analyses indicated that plants with foliar symptoms have lower microbial evenness than asymptomatic plants. The co-occurrence network modeled microbial interkingdom interactions. Molecular data generated in this study will help develop future targeted molecular quantification for specific taxa.

Spectral characterization of fungal diseases downy mildew, powdery mildew, black-foot and Petri disease on Vitis vinifera leaves

ABSTRACT Phytopathogenic diseases impact the development and yield of grapevines, resulting in economic, social and environmental losses. Sick plants have their metabolism changed, leading to alterations in their reflectance spectra. Little is known on these alterations, and a better knowledge could be used in the development of sensors able to detect diseases through fast, non-destructive techniques. This study was aimed at detecting spectral changes of grape leaves (Vitis vinifera cv. Cabernet Sauvignon), with early symptoms of downy mildew (Plasmopara viticola), powdery mildew (Uncinula necator), black-foot (Dactylonectria macrodidyma) and Petri disease (Phaeoacremonium spp.). Plants grown in pots and kept in a greenhouse were inoculated with the pathogens. In early stages of disease development, reflectance measurements were performed using a FieldSpec 3 spectroradiometer with leaf-clip attachment. The investigation began with discriminant analysis, which revealed that symptomatic plants are separated from the control ones. Reflectance spectra were, therefore, further investigated, looking for alterations on the shape of the spectra, characteristic of each disease. The disease descriptors were based on ratios between spectral features internal to a spectrum, a procedure which allowed the derivation of parameters intrinsic to each disease. A set of thresholds, defined as the ratios of reflectance at selected wavelengths, were derived for the studied diseases. For these ratios, the selected wavelengths (nm) were R443/R496, R443/R573, R443/R695, R443/R1900, R496/R573, R496/R695, R516/R1900 and R1900/R2435. The spectra from symptomatic plants present shape changes of as much as 20% with respect to healthy plants. The observed spectral changes are larger for black-foot and powdery mildew, but some wavelength ratios are also indicators of downy mildew and Petri disease. Data from wavelengths shorter than 700 nm in general carry more information than measurements at near infrared. These results are potentially useful to the development of low-cost devices to field use, providing real-time disease detection to early assessment of vineyard health status.