Beyond a few pro-forma appearances as a bibliographic reference, Lionello Petri's work on grapevine trunk decline lay in obscurity from 1912 to 1998 when Dr. Laura Mugnai retrieved it from an Italian archive and Dr. Luigi Chiarappa translated a summary in English for a small international workshop in California. After 86 years of obscurity, it took only six years and four more workshops for Petri to become a familiar name, albeit of a disease, in the grape industry.

The International Council of Grapevine Trunk Diseases (ICGTD) is a nonprofit organization, which operates on a volunteer basis with no sponsors or membership fees. In 2001, this group, which includes grape industry practitioners as well as researchers, was recognized as a subject matter committee by the International Society for Plant Pathology (ISPP).

Credit for the founding of this organization and rapid acceptance by the scientists worldwide goes to retired plant pathologist Dr. Luigi Chiarappa, whose doctoral thesis from the University of California Davis (UCD) was on black measles (Esca) in grapes. Currently, the focus is on the fungal agents of Esca and other diseases of grape wood, including Eutypa, Botryosphaeria, Cylindrocarpon and Phomopsis.

South African Workshop

Jointly organized by the South African Society for Plant Pathology and the South African Society for Enology and Viticulture, the 4th International Workshop on Grapevine Trunk Diseases (IWGTD), "Esca and Grapevine Declines," was held in South Africa. Grape research on vine health at the University of Stellenbosch, ARC-Infruitec and the now private KWV Vititec facility is first-rate.

Countries represented at the 4th International Workshop on Grapevine Trunk Diseases conference, included: Argentina, Australia, Chile, France, Germany, Greece, Hungary, Italy, New Zealand, Portugal, South Africa, Spain, Switzerland, The Netherlands and the U.S.

Although there is still much work to be done to understand exactly which organisms are causing which disease syndromes and to find "silver bullet" cures, it is clear that all research to date points to the efficacy of basic sanitation to minimize vine decline caused by fungi. Simply stated, if hard to achieve, one must start with clean cuttings and keep them clean:

1. Taking a bath: Scientists have demonstrated the effectiveness of hot-water treatment (HWT) in eliminating or greatly reducing decline organisms in nursery material. However, nursery representatives have indicated that there can be problems with survival rates. Therefore, additional research into the optimum methods of HWT under different growing conditions is needed before this becomes a universal practice.

2. Sanitizing tools and wounds: Nursery sanitation, field bleaching of shears and wound dressings all have been found to significantly reduce the incidence of Esca over the long term. Various fungicides were cited as being effective against the pathogens. Tebuconazole and flusilazole showed promise against both Eutypa lata and Botryosphaeria spp.

Biological controls, including Trichoderma and Fusarium, have shown some effectiveness as wound protectants in trials, yet there is still much debate over their usefulness in a commercial setting, due in some part to significantly different environmental conditions for those who have tried them.

3. Take out the trash: Remove pruning wood and either burn it or compost it. Take a good look at dead wood on the vineyard floor and you may find small black "dots" of fungal perithecia (or pycnidia) on the bark. These fungal bodies provide a reservoir of spores to be released by rain or irrigation water. Because many of the wood disease agents become imbedded in trunk and cordon tissues, cane pruning and trunk renewal programs are cultural ways to reduce problems and enhance vine longevity.

Not only is grape wood a source of inoculum, but the woods surrounding a vineyard may also be a source of disease. Researchers at UC Davis found Phaeoacremonium mortoniae in declining ash trees surrounding vineyards and also on Esca-diseased grapevines. Whether this species of Phaeoacremonium is a causal agent of decline in either of these plants has not been established.

4. Get regular check ups: Diagnosing vine decline issues requires experienced mycologists and pathologists. New disease identification techniques have been presented at each of the IWGTD meetings. A group from Penn State University, including Barry Overton, Elwin Stewart and Nancy Wenner, has developed a cost-effective method of detecting the Petri disease organisms and Tomato Ringspot Virus in live vines using real-time PCR methods. Such methods are particularly useful to nurseries and those maintaining foundation propagation material. It overcomes the high cost of destructive sampling, where clean plants are destroyed along with diseased ones.

Rod Bonfiglioli runs the state-of-the-art Linnaeus laboratory for Riversun Nursery in New Zealand, which can test for an impressive number of fungal (via cultural or molecular means), bacterial or viral disease in grapes. I asked Bonfiglioli to provide details of his diagnostic capabilities, to which he replied:

"We do ELISA for GLRaV1, and 3 in a big way (over 120,000 tests per annum). ELISA for GLRaV-2 and GVA at 20 percent of the above. ELISA for GLRaV-6 and 7 for quarantine work.

"PCR testing for GLRaV-1, 2, 3, 4, 5, 7, 9, and Alfie virus (see GLRaV-2 variants), GFLV (grapevine Fanleaf), Arabis mosaic (GArMV), GVA (Kober stem grooving), GVB (Corky bark), GVD, Rupestris stem pitting, grapevine fleck virus, grapevine phytoplasmas, Pierce's disease, TBRV (Tomato black ring), the American fanleaf degeneration complex, chrome mosaic virus and probably half a dozen more viruses of vines.

"We also do fungal culturing for phaeomoniella, cylindrocarpon species, botryosphaeria species (around five common species in NZ at this time), fusariums, alternaria, cladosporum, botrytis, eutypa, phytophthora species, pythiums; you name it: whatever is out there, we can grow. We also do general bacterial cultures, but the suspects are poorly characterized so we don't focus on this much: mainly virology and mycology.

"We do all our own diagnostics for MAF quarantine requirements, which also includes woody and herbaceous indexing, as well as many nameless and mind bogglingly insignificant viruses."

Esca appears in random pattern

Given that Esca has turned out to be a complex of diseases, researchers are now careful to study each of the fungal organisms separately. There is still much to be learned about this "now-you-see-me-now-you-don't" disease. In a young vineyard (7-10 years), diseased vines are found in random patterns. The infection will have been introduced via infected plant material or via aerial spores. In older vineyards where one finds groupings of infected vines, they seem to be more linked by site conditions than by infected neighbors. This suggests the role that vineyard conditions may play (water, nutrition, rooting depth, vine size-health, etc.). Weather effects are also apparent. In Italy, cooler and rainier seasons are linked to greater expression of foliar and fruit symptoms.

Fungal Taxonomy

While at first skeptical of the taxonomic labyrinth of Latin minutiae, I have come to appreciate how important it is to solving the many mysteries of vine disease. Latin is alive and kicking as the language for international communication in plant pathology.

Pedro Crous moved from South Africa to the Netherlands to head the Centraalbureau voor Schimmelcultures, the world's main mycological collection. Along with his predecessor, Dr. Walter Gams, Crous provided the "missing link" between Petri's studies of vine decline and Chiarappa's studies of Esca/black measles through his classifications of the genera Phaeoacremonium and Phaeomoniella.

There are lumpers and splitters in this world, and Crous is definitely a splitter when it comes to separating and renaming fungal genera and species based on their morphological characteristics and DNA sequences.

At the 2005 IWGTD meeting, Crous' colleague Lizel Mostert reported that 14 new species of Phaeoacremonium have been added to their list. Furthermore, some of these species can live in grapevines and grape growers alike. The following species are found in both Vitis and Homo sapiens: Pm. alvesii, Pm. krajdenii, Pm. parasiticum and Pm. venezuelense.

Old diagnoses of Pm. inflatipes were actually Pm. aleophilum or one of the new species.

Not all of these Phaeoacremoniums are necessarily significant disease agents. However, Crous and his team are now at work on another fungal family that is definitely of interest to grape growers. They are now delving into the taxonomic features of Botryosphaeria, which already has a trail of other names in the literature (Sphaeropsis, Diplodia, etc.), with new ones no doubt to follow.

While "bottom-liners" in the group have a difficult time appreciating the relevance of such efforts, researchers have shown that by no means are all species created equal. Think of the genus as a family name like "Smith" and know that the species can be as different from each other as you are from your sisters and brothers.

Wood decline fungi in the wilds of Iran

Reporting on his travels in Iran, Tom Grafenhan of Germany found fungal pathogens including Phaeomoniella chlamydospora, Phaeacremonium sp., and Euptya lata organisms on both wild and domestic grapevines. This raised questions about the origin of these fungi and their dissemination worldwide and the implications for differing genetic resistance among Vitis species, including those American species used as rootstocks. Furthermore, his observations highlighted the fact that "pathogenicity" is in the eye of the beholder.

Wild vines are creeping masses of tangled dead branches with skinny shoots on the periphery and an occasional ratty cluster. Domestic vines are confined to the same small space for decades and are expected to have no dead branches plus a fruit-to-shoot ratio of up to 10 to 1. Thus, low-level pathogens in the wild can become much more problematic in civilization, especially when introduced to new hosts in new environments. No one notices if a wild horse is lame, disheveled and riddled with parasites; but if he earns a post at the Derby, that becomes another matter.

It is common sense that vines are less able to withstand the internal damage caused by pathogenic fungi if they are malnourished. Diseased vines will suffer sooner than healthy vines in stressed conditions. By the same token strong vines with low levels of infection may show little signs of disease for many years. While they cannot be considered "cures," nutritional supplements via programs such as Agro-K and Brotomax have helped growers improve the performance of vines known to be infected with decline pathogens. Foliar applications provide an entryway for nutrients that bypasses clogged vascular vessels.

Stellenbosch Summary

In a recent article for the South African wine industry guide, Wynboer, Dr. Paul Fourie, Plant Pathology, Stellenbosch University, summed up the take-home messages for him of the workshop as follows:

"Apart from the contacts and collaboration agreements, we identified several research priorities and shortfalls in the local research programs:

• It was clear that, apart from the primary Petri disease pathogens that can initiate Esca [Phaeomoniella chlamydospora and Phaeacremonium sp.], the wood-rotting pathogens of the Esca disease [various basidiomycetes species] in South Africa differ from that in other countries in the world.

• The role of toxins in Esca and other diseases, such as Petri disease and Eutypa, are not properly understood in the South African context.

• Stress plays a significant role in trunk diseases, but the host-pathogen-environment interactions are not clearly understood yet.

• In most instances, deterioration and dieback of vine is a syndrome caused by a complex of pathogens. Only in a few instances, therefore, can disease diagnosis identify a single pathogen as the primary cause.

• Grapevine trunk diseases cause qualitative and quantitative crop losses in all winegrowing countries in the world. Effective control depends on the prevention of infections in nurseries and vineyards, and in most cases is based on wound protection."

Next stops: California and Italy

At the Stellenbosch meeting, the "academy award" went to the UC Davis team of Akif Eskalen and Suzanne Rooney-Latham for their spellbinding video capturing the discharge of ascospores from the moistened perithecia of Togninia minima (Phaeoacremonium aleophilum). I could see participants marking their calendars for the next workshop (fall 2006) to be held in Northern California, organized by the UC Davis Department of Plant Pathology (contact Dr. Doug Gubler wdgubler@ ucdavis.edu). Dr. Mugnai has suggested Turin, Italy for the 2008 meeting.

Presentations at the ICGTD workshops are highly technical. At the same time, they are well illustrated and linked to practical issues in the vineyard, such as overhead irrigation, wound protection, timing of pruning and nursery practices. I would recommend that more industry members attend future meetings to see the remarkable progress that has come in a short time on this hitherto ignored area of viticulture.

News from New Zealand

The issues that affect the propagation and production of nursery grapevines have become increasingly industry-specific and challenging. Not long ago, while attending the IV Grapevine Trunk Disease Workshop in South Africa, a loosely-knit group of interested individuals came together to start planning how they might create an international coalition that would bring together grapevine nursery practitioners to share best practices and current concerns.

An additional goal is to organize a related conference that is a blend of business, best practices and scientific presentations in areas where a clear business advantage can be gained, such as the management of virus and fungal problems. As a means of testing the waters to determine the level of interest and commitment such a project could generate, the group is now developing a preliminary list of email contacts and will post a web-based survey in the near future.

If those interested in grapevine plant material come together in the same collegial, professional and focused manner as the ICGTD members, there could be a jump in vine improvement for growers worldwide.

For their part, growers need to shed their apathy in the matter of the health and pedigree of their plant material and take an interest. Let's join the world of dogs and wine and develop industry-sponsored competitions where nurseries and research centers enter their benchgrafts, rootings and clonal selections seeking recognition as "best in show." wbm

For membership information regarding the International Society for Plant Pathology (ISPP), contact the Chairman, laura.mugnai@unifi.it.

For information on the formation of a grapevine nursery practitioners coalition, contact Ruby Andrew at ruby.andrew@xtra.co.nz. He host for the first (2008) meeting will be Riversun Nursery in Gisborne (www.riversun.co.nz).