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Researchers will use nearly $1.8 million in grant money to develop new detection, extension, and research tools for managing wood-canker diseases of grapes and nut crops. Wood-canker diseases are a leading cause of vineyard and orchard removal in many parts of the country.

The research project was one of 14 projects funded in October by the U.S. Department of Agriculture’s Specialty Crop Research Initiative authorized under the now expired 2008 Farm Bill. A total of $46 million was approved for the SCRI projects.

This is the first multicrop project to tackle trunk ­diseases. Several trunk diseases affect all three of the crops involved in the study—grapes, almonds, and pistachios. For grape growers, the project aims to stem losses of yield and longevity of the vineyard from grapevine trunk ­diseases, the primary ones being Eutypa, Esca, and Botryosphaeria. Dr. Kendra Baumgartner, plant pathologist for USDA, heads the research. She is stationed at the Agricultural Research Service facility in Davis, California.

Research objectives are to develop detection ­technologies, identify sources of disease resistance, and encourage adoption of preventative practices.

Wood-canker diseases

Wood-canker diseases are problems in many grape growing regions due to their detrimental effect on yield and the life of the vineyard, Baumgartner said in a phone interview with Good Fruit Grower. Symptoms of wood-canker diseases include dead spurs, arms, and cordons. Eventually, the vine dies due to canker formation in the vascular tissue.

“Wood-canker diseases are difficult, because the most obvious symptom of rotted, brown wood is inside the vine and you can’t see it unless you cut into the trunk or cordon,” Baumgartner said.

“Sometimes, growers will notice some shoot dieback or that shoots aren’t pushing out in the spring. Or they may cut into a specific spur or cordon that doesn’t look right to see if something’s going on. But that’s not an ­efficient way to look for disease,” she said, adding that growers may inadvertently cut into healthy wood.

Symptoms often don’t show up in vineyards until several years after infection, typically when the grapevines are seven years or older. Detection usually comes much too late to control the diseases, both for growers and researchers, she said.

Moreover, wood-canker diseases are not just grower problems. “There have been a lot of accusations of nurseries selling infected plant material. But is that due to poor treatment and neglect of the disease in the field, or because there aren’t any standards for wood-canker ­diseases for nurseries to follow?” she asked.

Early detection

A key goal of the project is early detection. The research team will pioneer the use of a high-powered type of X-ray, similar to a CAT scan, to look inside the grapevine for changes in the woody stem. The specialized equipment is located at the Lawrence Berkeley National Laboratory in Berkeley, California.

The high-resolution technique was used in an SCRI project studying water stress in grapevines. “If we can use the same technique, we can learn about the development of wood-canker diseases inside the plant,” she said, adding that whole plants from the greenhouse used in their research could be scanned. The technique could also help researchers learn how resistant cultivars respond to the infection.

The research team plans to develop early detection tools for diagnostic labs, nurseries, and growers that would sample healthy leaves in the early stage of infection. By combining advanced molecular and imaging techniques to identify the molecular signature, they hope to develop a DNA-based technology that uses green tissue in detecting the molecular signature. Such a test using leaves would be more convenient, less destructive, and could be used by nurseries to detect the early stage of infection and limit planting of contaminated nursery stock.

Another early detection tool geared for the grower is a spore trap to measure presence and risk of disease. The research team is working with Coastal Viticulture Consultants to develop a solar-powered spore trap that would show presence of spores in the vineyard’s atmosphere. The California company already offers a powdery mildew spore-trapping program for growers.

“If growers knew that the threat of infection is there from the spore counts, that could help them justify the expense of preventative strategies, like adjusting their timing of pruning,” she said.

Planting disease-resistant cultivars is a time-tested and sustainable approach to disease management. A range of resistance exists among commercial grape ­cultivars, but information is limited.

Researchers will work to develop an improved, faster screening assay for evaluating commercial cultivars and USDA germplasm repositories for sources of disease resistance. Cultivars screened will include juice grape and table grape varieties that have been overlooked by international researchers who are mainly concerned with wine grape varieties.

Preventative practices

Economic analyses will be developed to help show growers the importance of using preventative strategies to better manage wood-canker diseases in young vineyards compared to taking drastic measures in older ones, like cutting dead cordons and replanting vines. Researchers will build an outreach strategy with new extension tools, such as smartphone applications, that encourage adoption of preventative practices.

A smartphone application is envisioned for growers to use in the vineyard to aid in early diagnosis. The app would provide photos detailing symptoms and give recommendations on how to take samples to confirm diagnosis.

“A disease like Esca is not common in Washington State, so if it came in on nursery stock and something looked suspicious, a grower might not even think of considering Esca as a potential disease,” she said. “A smart-phone app could be valuable in getting growers in the habit of considering wood-canker diseases—especially those who haven’t experienced these diseases—before they become problematic in the vineyard.”

The research project is supported by the National Wine Grape Initiative, a national coalition representing juice, raisin, table, and wine grape producers. Initiative members have committed vineyards for the trial and serve on the project’s advisory board. The SCRI grant provides funding for the first two years of a five-year project. Baumgartner hopes additional funding will come after completion of the first two years.

The project is transdisciplinary and includes a broad team of researchers. Principal investigator is USDA’s Dr. Themis Michailides, also at Davis. Other investigators include: David Doll, University of California Cooperative Extension; Mizuho Nita, Virginia Tech; Grant Cramer, University of Nevada, Reno; Philippe Rolshausen, UC, Riverside; Jonathan Kaplan, California State University, Sacramento; and Mark Lubell, UC, Davis.