Summary of Recent Visit to San Juan Province
By: Judit Monis, Ph.D.
This year I was invited to evaluate vineyard disease issues in different grape growing regions in the province of San Juan under the auspices of the Ministry of Agriculture. The program included the inspection of many producing vineyards (both for raisin, table, and wine grape production) as well as a grapevine nursery. As you know my interests are in how to prevent the spread and disease development in the vineyard. So, it will not be surprising that this article will highlight vine diseases observed in the region.
Mendoza and San Juan are the primarily grape growing regions in Argentine
Argentina grows over 200,000 Hectares of grapevines that are plated mainly in the provinces of Mendoza, San Juan, La Rioja, and Salta. The industry has expanded to other areas in the provinces of Buenos Aires, Cordoba, Rio Negro, and Tucuman. However, the majority of the vineyards are located in different regions of Mendoza and San Juan. This is why there is a saying in Argentina that a person is between San Juan and Mendoza when drunk! These two provinces have chosen to differentiate their growing, Mendoza focuses on producing its famous red grape variety Malbec, while San Juan grows white wine, table and raisin grape varieties.
Argentina ‘s viticulture is different from what I am used to seeing in Californian or Chilean grape growing regions. Most of the vineyards in Argentina have planted vines on their own roots (i.e., these are not grafted onto a rootstock) as the phylloxera pest is not present in most Argentine grape growing regions. Obviously, rootstocks confer resistance to phylloxera, but also help grow grapes in areas where nematodes and salinity are a problem. Rootstocks also control the vigor of the vines in the vineyard and many winemakers consider that there is an effect on wine quality and sensory aspects. Consequently, more vineyards in Argentina are being planted with grafted vines, especially in Mendoza’s newer and more sophisticated growing regions such as the Valle de Uco.
Grapevine Diseases Originate Where Vitis Species Originate
We know that grapevine pathogens (disease causing agents) originated in the same place where Vitis (the grapevine genus) species originated. These disease agents (bacteria, fungi, and viruses) were introduced to other places in the world with the grapevine propagation and planting material. Specifically, the varieties and clones that are grown in vineyards around the world belong to the Vitis vinifera species (of Eastern European and Asian origin) while the rootstocks grown commercially belong to American Vitis species. When grape cultivation started countries were not set up with quarantine programs, neither modern diagnostic tools we use today (deep sequencing, PCR, ELISA, etc.) to detect pathogens were available. Consequently, since the early days of grapevine cultivation European and American grapevine pathogens have been moving from one site to another for many generations.
Grapevine Diseases are Found Wherever Grapevines are Grown
When it comes to diseases, Argentine viticulture is not different from other worldwide growing areas. The commonly known diseases caused by Leafroll viruses, Vitiviruses, Fanleaf, Agrobacterium vitis, and fungal trunk pathogens arrived on site when plant material was imported. Even Grapevine red blotch virus (GRBV) considered an American virus has been reported to be found in Argentine vineyards. These are important diseases that affect both grape quality, yield, and longevity of the vineyards. In Argentina, I have witnessed the presence of Syrah Decline, a disorder that affects both grafted and non-grafted plants. However, we now know that Syrah Decline symptoms are linked to genetic markers present in certain Syrah and Shiraz clones. Research in France elegantly demonstrated the generic nature of the syndrome, therefore Syrah Decline can be prevented by avoiding to plant certain genotypes of this grape variety.
Growers and Nurseries Show Interest in Grapevine Certification Programs
Grape growers and winemakers are aware of the detrimental effect of grapevine pathogens and would prefer to purchase and plant disease-tested (certified grapevines). In Argentina the grapevine certification program has gone through administrative revisions. Laboratories are being certified by an entity (INASE) to offer testing to allow vines to be part of the certification scheme. The law allows the application of molecular (PCR, ELISA) instead of biological indexing to detect viruses in the foundation and nursery increase blocks. Interestingly, the certifying agency does not administer a foundation block. Instead, each private nursery has their own foundation block. The viruses excluded are Grapevine leafroll-1, -2, -3, and -4, Vitiviruses A and B, grapevine fanleaf, and grapevine fleck. Unfortunately, even if GRBV was detected in Argentina, it is not included in the testing requirements at the moment.
Evaluation of Vineyards in the San Juan Province
During my visit I was able to appreciate the diversity of grapevines grown in San Juan. The vineyards evaluated included table, raisin, and wine grape variety vineyard blocks. Some of the vineyards were mature and others were planted within the year. As expected, the symptoms observed in the different blocks were as diverse as the varieties planted. My visit coincided with the beginning of the fall season, in the middle of the busy harvest season in South America. This is my favorite time to inspect vineyards since the symptoms of viral diseases (such as leafroll) are most noticeable (see Photo 1-Lead Photo). In the table grape varieties, we were able to observe lack of color and delayed maturation of the fruit that could be due to viral infection (Photo 2).
Vines with notable decline due to potential fungal infection were also observed. The vines were marked and samples will be collected (after the harvest is completed and leaves fall) to test in laboratories to determine the cause of symptoms. We will work with three different Argentine laboratories (two of them I have helped with protocol development) to compare their proficiency (i.e., we will conduct and inter-laboratory comparison). My week-long visit culminated with a presentation I delivered to growers, nurseries, and ministry officials focusing on suggested preventative disease strategies and discussion on the findings during the vineyard inspections and future steps that will follow.
Conclusions
My involvement with the San Juan province project will continue as we work with the growers, nurseries, and laboratories to develop sampling and testing protocols. I am also planning to help the nurseries develop sanitation and testing programs to allow them to propagate only plants that are not infected with pathogens of concern. It is my hope that, with time, future changes will include the availability of certified pathogen free tested and true-to-type scion and rootstock planting material. Only with clean planting grapevine material these important grape growing areas will see an improvement on the health and longevity of their 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 their vineyard blocks. 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.
