Symptoms of decline and cankers in grapevines of Seimatosporium species, a fungal pathogen
By: Judit Monis, Ph.D. – Vineyard and Plant Health Consultant
Grapevine trunk diseases occur worldwide and are caused by bacterial, fungal pathogens, or a combination of both. Trunk disease fungal pathogens can be airborne and soilborne. These pathogens not only affect grapevines but other fruit and tree species and can be found colonizing the orchard or vineyard soil. Grapevine stock material can be infected with important pathogens which makes it important to test and inspect nursery material for their presence prior to planting.
This article will focus on the description of common grapevine trunk diseases caused fungal pathogens, their causal agents, and best prevention and management practices.
Description of Main Fungal Trunk Diseases
Petri Disease, Young Vine Decline, Esca: The disease in young vines, known as young vine decline or Petri disease, is caused by species of Cadophora, Phaeoacremonium, and Phaeomoniella. In older vines, the same fungal pathogens can cause Esca disease. Wood symptoms include brown gummosis, pitting, or streaks and typical foliar discoloration known as tiger stripes. The disease is chronic when vines express a gradual decline of symptoms over time, or acute when the vines decline and die within a few days. These acute symptoms are known as the apoplectic stage of the disease. It is not uncommon during the apoplectic stage of the disease to see dead vines carrying mummified grape bunches. I have inspected vineyards that had their vines decline and die within the week of the appearance of symptoms.
Canker Diseases: Various pathogens can cause canker symptoms, large discolored areas in trunk and cordon in the vineyard. Bot-canker or dead arm disease is caused by different species in the Botryosphaeriaceae family. The most severe Bot-canker species is Lasidiplodia theobromae, while weaker symptoms are caused by Diplodia species. Eutypa dieback is caused by different species in the Diatrypaceae family. The most common species is Eutypa lata, but species of Criptovalsa, Diatrypella, and Eutypella can also cause canker disease in grapevines. In my lab we characterized Seimatosporium species as a fungal pathogen that causes decline and cankers in grapevines (see Photo), but within the same fungal family Pestalotoipsis and Truncatella have been reported to cause disease in grapevines. Another canker pathogen is Diaporthe (also known as Phomopsis). The canker symptoms observed in the sections of affected cordons or trunks in grapevines have similar symptoms but may be caused by unrelated fungal species with different life cycles and mode of infections.
Black Foot Disease: Species of Campylocarpon, Cylindrocladiella, Dactylonectria, and Ilyonectria (previously known as Cylindrocarpon spp.) are the causal agents of this complex disease. These fungi are soil-born and most active on compact soils with poor drainage. Above ground, the symptoms of black foot disease can be indistinguishable from the decline symptoms described above for young vine decline or Pierce’s disease (caused by the bacteria Xylella fastidiosa).
Sudden Vine Collapse Syndrome: Due to the vegetative propagation of grapevine plants coupled with grafting and pruning activities, it is common to find diverse fungal and viral species infecting the same vines. Vines affected with the Sudden Vine Collapse Syndrome have been found to be infected with fungal pathogens and Grapevine leafroll-3 (GLRV-3) and Vitiviruses. These vines are known to die within a short period of time after symptom development. In my opinion, the symptoms of this syndrome are not different from the apoplectic stage of Esca. However, not always the same fungal pathogens are found associated with the syndrome. In my lab, we have found a combination of Esca pathogens combined with Botryosphaeriaceae species, GLRV-3 and Grapevine virus F (a Vitivirus). In some cases, additionally we have found Basidiomycete (fungi that produce mushrooms as fruiting bodies) species associated with the symptomatic vines. Academic researchers who have studied this syndrome concur that it is caused by a combination of viral and fungal pathogens (not always the same usual suspects!). In my experience working with pathogens that affect grapevine, the presence of various viruses and fungal species in the same vine is a common and they work synergistically to affect the health of the vines in the vineyard.
Root Rot Diseases: Species of Armillaria mellea (Oak root fungus), Phytophthora, and Verticillium are soilborne fungal species capable of causing decline and rots in the vineyard. Just as described above for black foot disease, these pathogens strive in compact soils with poor drainage.
Disease Prevention and Diagnosis: The best management and disease control measure available is to prevent the introduction of pathogens in the vineyard. Because of the complexity of infection, none of the US-certification programs exclude trunk disease pathogens. Therefore, propagation material is likely to be infected with various fungal pathogens. As a first step, it is important to inspect the quality of the planting material (graft union integrity, lack of galling, absence of streaking or pitting). A laboratory is best suited to provide specifics of the fungal pathogens present in a plant or soil sample. Fungal pathogens can be cultured and isolated in specialized media. However, even when using selective media, microorganisms are known to compete among each other. A fungal species that grows faster will expand over others that grow slower, making the identification of certain fungal pathogens difficult. In these instances, the diagnosis will be biased or the laboratory may not be able to report the disease causal agent unless sophisticated molecular methods are used. In some cases, the identification of the fungal taxonomic family (i.e., species of the Diatripaceae or Botryosphaeriaceae) isolated from a canker may be sufficient to decipher the cause of the problem. In my lab we developed methods to isolate DNA from these cultures and obtain a precise sequence to determine the identity of a fungal species. Recently, some commercial laboratories had started offering plant and soil testing using the next generations sequencing (NGS) technology also known as high throughput sequencing (HTS). This is a powerful method that allows a laboratory to detect any organism present in a sample. When NGS is applied, the complete sequence of the plant genetic material and its microbiome can be obtained. During preparation of the sample, it is possible to “enrich” the sequences of pathogens of specific interest. For example, the lab may amplify only fungal sequences prior to NGS, increasing the sensitivity of the assay. The data obtained is processed with software that analyzes the microorganism’s (beneficial or pathogenic) sequences present in the sample. The method can provide relative quantitative data, generally expressed in percentages, of each microorganism found.
Disease Management and Control: The implementation of appropriate sanitation measures at the nursery is most needed to produce high quality planting grapevine material. It is known that one infected vine can produce between 100 -200 vines each year, potentially producing a significant number of infected grafted plants. The use of hot water treatment (HWT) consists of soaking the plant material in hot water (122F = 50C) for 30 minutes at the nursery. In spite of the treatment reducing the population of fungal pathogens in the propagated vines, there are mix reports on the effect of the HWT on bud mortality. Reports in warmer winegrowing regions (e.g., Spain) have shown a lower effect on bud mortality compared to HWT in cool climate regions (e.g., Australia).
Many of the fungal pathogens that cause disease in grapevines are endophytic, meaning that they can live in the vine without causing disease. However, the same fungal species can become pathogenic during stress situations (lack of water, heat wave, etc.). Furthermore, because fungal pathogens cannot be completely eliminated in the vineyard once introduced, it is important to apply the best management practices available once planted at the vineyard. I recommend inspecting the mother vines and planting material to judge the quality of planting material. The high-quality planting material must be grown in well prepared and drained soil, at the correct season. Ultimately (and always!) the best practices in the vineyard must be applied (i.e., enough water, nutrients, etc.).
It is known that the effect of grapevine fungal pathogens increases as the vineyard ages because its fungal population continues to multiply yearly. Therefore, growers must adopt management and control measurements as soon as the vines are planted in order to prevent and minimize the propagation and dispersal of fungal pathogens.
Management at the vineyard should include trained personnel for pruning activities. In areas where the rainy season coincides with the pruning season it is recommended to prune as late as possible prior to bud break. Pruning late has the advantage that the produced wounds will heal faster, as the vines become active in the spring. Additionally, most fungal spores would have been depleted and unavailable to start a new infection, the later the pruning activity starts. If the vineyard size is extensive and does not allow workers to complete the activities before bud break, the double pruning method is recommended. This consists of pre-pruning the vines as soon as the dormant season starts, leaving canes of 1-2 feet long. In the late winter or early spring, pruning would be completed by leaving the desired number of buds per spur. The freshly produced wounds should always be protected using fungicides or a sealant such as Safecoat VitiSeal. I prefer the latter product because it provides a protective layer that does not allow the fungal spores to enter, does not affect beneficial fungi, and allows wound healing . During pruning it is important to avoid producing large wounds, cutting near the trunk, or pruning after long periods of rain. Finally, it is important to remove the vine residues in the vineyard floor as this would be a source of inoculum to start new infections.
Economic studies performed by Dr. Kendra Baumgartner and colleagues (USDA at the University of California in Davis) has shown that preventative methods (late pruning, double pruning, and pruning wound protectants) are sustainable only if applied before symptoms appear in the vineyard. Adopting these methods in older vines will not recover the cost of the treatments.
A more drastic disease management practice includes vine re-training also known as remedial surgery. The procedure consists of training a new shoot from the base of the trunk to replace the old decayed vine trunk or cordons. The technique can help gain some years of production but will not cure the vines from the disease as likely the pathogens are already established in the vine. When replacing vines, the grower must understand that many fungal pathogens can survive in remaining portions of the roots and soil, therefore new vines that are planted (even if free of bacterial or fungal pathogens) can become infected over time even if the vine roots are completely removed from the vineyard.
Other methods that have been reported for the management of fungal diseases include planting white mustard (Sinapsis alba) plants as cover crops that act as a biofumigant and the use of biological control agents such as Trichoderma species, and mycorrhizal fungi.
Conclusions: Due to the nature of fungal infections in the vineyard and surrounding areas, following precise management practices in the vineyard is the most important step in preventing disease development. Similar to viral and bacterial infections, fungal diseases are complex, as mixed infections are common and can exacerbate the symptoms in the vineyard. Consulting with a knowledgeable plant pathologist can help assess the potential of disease development based on the presence certain fungal species. The application of early and efficient diagnoses will help reduce the infection levels of propagation and planting material, consequently avoiding disease onset in the vineyards.
Judit Monis, Ph.D. provides specialized services to help growers, vineyard managers, and nursery personnel avoid the propagation and transmission of disease caused by bacteria, fungi, and viruses in the vineyard. Judit (based in California) is fluent in Spanish and is available to consult in all wine grape growing regions of the word. Please visit juditmonis.com for information or contact juditmonis@yahoo.com to request a consulting session at your vineyard.
