Seeking Answers for Grape Diseases
Gardeners may prize ornamental grapes that turn crimson in late summer, but that’s not something wine grape growers want to see in their vineyards. Crimson leaves are a characteristic symptom of a complex virus-associated disease called grapevine leafroll. The untreatable disease delays ripening, causes a significant drop off in yield and grape quality, and can shorten the life of the vine.
“It is becoming a major problem,” said Naidu Rayapati, a grape virologist as WSU’s Irrigated Agriculture Research and Extension Center in Prosser. A vineyard survey conducted several years ago detected leafroll virus in about 10 percent of the state’s vineyards. Anecdotal evidence suggests wider spread since.
While a small insect called the grape mealy bug is capable of spreading the virus, humans are probably the primary means of transmission, according to Rayapati. “When you are taking cuttings from a grapevine that is infected with the virus, you spread the virus to the place where these cuttings are going,” he said.
Since maintaining clonal integrity is the key to producing grapes that will faithfully fulfill a winemaker’s expectations, vegetative cuttings are the only means of propagation that will guarantee trueness to type.
In his laboratory in Prosser, Rayapati is studying the genetics of the viruses. He hopes that will lead to a greater understanding of the behavior of the viruses, more robust diagnostic tools and more effective means for managing the diseases.
“It’s truly translational research,” he said. “You look at the problem in the field. You then bring the problem to the lab and try to address it with the latest technologies and try to provide solutions.”
For more information, please visit Rayapati’s virus website: http://bit.ly/aR2rfU.
Virus Sensor May Lower Detection Costs
In the not too distant future, grape growers may be able to detect virus-infected grapevines in the field using a portable sensor that evaluates changes in the light reflecting properties of leaves. The sensor will speed detection and save money now spent in random testing to find infected vines.
Currently, there is no way to know for certain if a suspect vine is infected without lab testing. Costs for testing can quickly add up. The most reliable test–polymerase chain reaction–enables researchers to identify the DNA of low concentrations of viruses. It costs in the neighborhood of $40 per PCR assay, per virus, per sample. “If you have one sample and you want to check for six different leafroll viruses, that would cost $240,” WSU grape virologist Naidu Rayapati said.
Now, in the first study to report the possibility of using leaf spectral data to diagnose virus disease in a perennial woody species (e.g., grapes), scientists at the WSU Prosser Irrigated Agriculture Research and Extension Center found differences in the light reflectance data from leaves of infected and healthy leaves of two red grape varieties.
Eileen Perry and Francis Pierce, who are, respectively, assistant director and director of WSU’s Center for Precision Agricultural Systems, analyzed data collected with a spectral radiometer from leaves of two red grape cultivars showing symptoms of grapevine leafroll. The reflectance properties were compared with leaves from non-infected plants. Rayapati then compared the analysis with results generated by RT-PCR, a molecular diagnostic tool, to learn which spectral features could be correlated with leafroll virus in living plants.
The end product of the research could be a handheld instrument that would enable growers to screen plants in the field. “Ideally, you wouldn’t have to go through and grab leaves randomly off vines or select vines randomly,” said Perry. “You would have a better idea of which plants were infected or likely to be infected.”
“Even if we can achieve 80 percent success with this kind of technology,” Rayapati said, “it will help us tremendously in terms of cutting down the cost and speeding the process of testing.”
The study was published online Jan. 19 in the peer-reviewed journal Computers and Electronics in Agriculture. It can be reviewed at http://tinyurl.com/grapesensor.
Go North, Young Man!
WSU freshman Derek Herman is proof of the Washington state wine industry’s growing reputation.
Herman is a viticulture and enology student who grew up in the San Francisco area. With Napa Valley and Sonoma County just a short drive from San Francisco, most students interested in grape growing and winemaking attend schools in central and northern California with well-established viticulture and enology programs. However, for a variety of reasons, Herman chose WSU.
“Where I’m from, wine is a big thing. I did apply to the schools down there, but Washington State’s is new and I wanted to be a part of it,” Herman said. “Also, I wanted a big school that has spirit and is part of a major conference like the PAC-10. Everyone here is into the school and has the ‘Go Cougs’ spirit, which I like.”
Herman’s first contact with the school came in San Francisco where WSU professors Carolyn Ross and john Reganold were delivering a lecture on viticulture and enology. “I was able to go to the lecture with my parents and meet with some very important people from the university, including President Elson Floyd. Everyone was just so nice, and that really sparked my interest,” Herman said.
“I’m just getting into the viticulture and enology program, and I’ve really liked what I have done so far,” Herman said. “Pullman is a lot smaller area than where I am from, but I like that. I even like the snow.”
by Mitch Sieber, Voice of the Vine intern