From PCR to Garden Seed Potatoes

Leveraging grower investment with specialty crop funding

Published online: May 29, 2018 Seed Potatoes Nina Zidack, Montana Seed Potato Certification Program
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This article appears in the June 2018 issue of Potato Grower.

Since Jim Shepard’s development of the radial diffusion assay for PVY and PVX in 1969, Montana has been the leader in high-throughput testing for viruses in seed potato certification. In 1978, ELISA was implemented on an even larger scale for virus detection. Just as ELISA testing has become the workhorse of certification testing, polymerase chain reaction (PCR) has been emerging as a faster and more sensitive test compared to traditional serological assays. When I arrived in 2008, PCR had evolved to a point where it became the new standard for sensitivity in diagnostics, and was rapidly becoming more adaptable to high-throughput testing. Although the lab possessed a base level of capability, we were not ready to scale up the test in a high-throughput manner to respond to industry demands. This is the point that we determined we needed outside resources to ramp up our diagnostic capabilities.

When you hear reports out of Washington about the farm bill, you may not realize the work that is supported within states to perform ag research and enhance marketing. The Specialty Crop Block Grant (SCBG) Program funded through USDA has been exceptionally beneficial to Montana seed potato growers. The first funding we received was to address the need for actual implementation of PCR in our program and to adopt and validate PCR protocols for PVX, PVY and PVA.

Through this first grant, we established detection limits for the three viruses in comparison to ELISA for leaf, sprout and tuber tissue. We also demonstrated that we could detect very low titers of virus, and that it was a valid technique for assaying tuber tissue. We built upon this program with a project evaluating real-time PCR, an improvement on conventional PCR as a quantitative measure, with increased sensitivity. These projects enabled us to validate detection methods for 10 potato viruses, three bacterial pathogens and two fungal organisms (late blight and powdery scab). Following this success, in 2012 our lab purchased a real-time PCR instrument through SCBG funding (with Montana Potato Improvement Association matching funds), enabling us to further increase our testing throughput. In 2013 we began testing dormant tubers as a service to our growers. That first year, we tested over 8,000 tubers and have tripled that number with this past season’s post-harvest testing. In the future, we plan to explore additional methods, including robotics to improve our testing capacity.

In 2012, we also obtained funding from an SCBG to survey garden seed potatoes that were coming into the state. Montana has a closed seed potato certification system and does not allow seed potatoes from outside Montana to be re-certified. However, we do not have control on what comes in for commercial potato production or garden seed. Survey results of potatoes imported into Montana through retail outlets, mail-order catalogs and internet sales revealed that many lots had no certification labels or information on origin. In two years of testing, our lab detected PVY in 40 percent of the seed lots; the average level of PVY in the infected seed lots was 31 percent. In a third year of testing, we detected similar levels of PVY, but even scarier was the detection of bacterial ring rot in two samples originating from catalog purchases. This revealed a significant threat to our seed potato production areas and heightened the urgency for insuring that healthy certified seed potatoes be planted in home gardens.

In any given year, Montana certifies 70 to 80 potato varieties, including many specialty varieties demanded by home gardeners. Still, we did not have an effective means to get these varieties from producers to retailers and ultimately to the gardeners.

SCBG funding was again pursued to develop a garden seed directory, website and distribution network to get Montana certified seed potatoes into the hands of home gardeners. The first three years of the distribution network, the Montana State University potato lab gathered over 20 varieties of seed potatoes from growers and delivered them to county extension offices, garden centers, truck gardens and home centers throughout the state. This dramatically improved the availability of Montana certified seed potatoes and also supplied the gardeners with a fantastic variety of potatoes. In 2016, the ultimate goal of this project was realized when one of our seed potato farms, Holbrook Seed Potatoes, owned by Scott and Laci Holbrook, took over the network. The Holbrooks are selling their own seed potatoes as well as seed from other Montana growers with the same clientele as a base. “The program has been rewarding in that we get to meet some amazing people who are excited about Montana certified seed and very happy with the quality,” says Laci Holbrook. “It makes me wonder what the seed they purchased looked like before. Also, I hope we are doing our industry a service in preventing some very diseased seed from coming in from out-of-state.” 

Montana seed potato growers are visionaries in the U.S. potato industry who employ the latest developments in agricultural technologies to produce high-quality seed potatoes. They have invested heavily in instrumentation and staff for diagnostics of potato diseases. The ability to leverage their investment and vision through SCGB funds will ensure that our diagnostic programs will evolve to meet emerging challenges to seed potato health.