1. Virus indexing is a method used to determine the presence and identity of sweetpotato viruses.  The Brazilian morning glory (Ipomoea setosa), a close relative to sweetpotato, is sensitive to sweetpotato viruses. I. setosa is referred to as an indicator species because when infected sweetpotatoes are grafted to it, virus symptoms develop and ‘indicate' that the plant is infected with viruses. Polymerase chain reaction (PCR) assays are also used to detect nucleic acids of specific viruses.
2. Virus-tested means that plants have been screened and found apparently negative for the presence of known or targeted viruses affecting sweetpotato.
3. Scientists avoid the term "virus-free" because we only test for viruses that are known to infect sweetpotato. Furthermore, it is impractical to test every plant produced by the NCPN- Sweetpotato Clean Plant Centers, an estimated 384 million plants in 2017.
4. The term “clean plants" refers to sweetpotato plants generated through a uniform process agreed upon by NCPN- Sweetpotato Clean Plant Centers. This includes standardized virus-testing procedures, plant therapy to generate nuclear stock plants free of known sweetpotato viruses, and collaboration with state regulatory and crop improvement agencies to limit reinfection during the propagation of clean plants in greenhouse and field environments.
5. Reinfection happens when clean plants are exposed to sweetpotato virus vectors. Sources of viruses may be wild morning glories or cultivated sweetpotatoes. Aphids vector the most common group of sweetpotato viruses in the U.S., but whiteflies also transmit some uncommon sweetpotato viruses.

Matthew Garber

“Garber Farms grows over 1,000 acres of sweet potatoes annually. Our average yields over the past 10 years has steadily increased to around 675 bushels per acre. The Foundation seed program provided by LSU has been the core input of our production practices. Its ability to provide Garber Farms with a viral-and disease-free clean plant product has allowed our transplants to have the potential to produce higher yields. In our climate of high humidity and high temperatures, virus and disease pressures are extreme, so we keep our plant production within two generations of the G-1 viral free foundation seed furnished by the LSU Experiment Station.

The clean plant program has given our commercial production the economic confidence to increase all input levels in a constant effort to reach for greater financial returns per acre. While we seldom plant past G-3 seed, when we have tried G-4, it has been obvious that yield potential drops significantly. The quantity and quality decline results in revenue reduction of 25 to 50 percent.

The future of our sweet potato industry is directly dependent on the continuation of LSU's Clean Plant Program. We are grateful for the quality of our research and researchers who provide the underpinnings of our efforts to remain competitive and financially profitable into the future.”

Duane Hutton, sweetpotato packing shed manager, Livingston California

“Clean seed improves yield, quality, shelf life, and packout efficiency of our sweetpotatoes. Yield is 10-20% better with clean seed. Quality makes the produce buyer's business more efficient and pleases their consumers. Sweetpotatoes harvested from clean seed last longer in storage bins. Clean seed sweetpotatoes require less labor to pack. With clean seed we have first class yields; no excuse, top quality; good shelf life; and a smooth packing operation.”

Wade Fleming, sweetpotato producer, Calhoun County, Mississippi

“In 2016, we grew foundation and older sweetpotatoes next to one another in the same field. The foundation sweetpotatoes yielded 100 bushels per acre more in the same field.”

Matt Alvernaz, sweetpotato grower, packer, shipper, Merced County, California

“The cleaner the seed, the less virus you'll have, and the more saleable product you'll have.”

You'd think something named “sweetpotato” would be a bit more attractive, but the tuber's lack of visual appeal can be forgiven once it hits the palate. Sweetpotatoes are an excellent source of beta-carotene, vitamin A, antioxidants and anti-inflammatory nutrients. But let's be honest—the sweetpotato's real charm is its versatility in providing a vessel for melted butter, cinnamon, curry, raisins, and a host of other sweet and savory flavors. So we are most fortunate that this old-world vegetable has become one of the newer specialty crops in the National Clean Plant Network. As one of 7 crops in the network, sweetpotatoes benefit from the attention of scientists and growers who are committed to protecting the species from harmful viruses. Such a team of sweetpotato saviors staff a clean plant center at Louisiana State University.

Dr. Chris Clark and Emily RIngeman are part of the expert team that manages the Sweetpotato Clean Plant Center at Louisiana State University AgCenter. Over 60 years of collective experience are represented by the team members who collaborate across two locations: the Sweetpotato Research Station in Chase, and the Plant Pathology & Crop Physiology program in Baton Rouge.

Virus therapy, tissue culture propagation, and virus testing are conducted on the LSU campus in Baton Rouge by Emily Ringelman and Chris Clark. Emily came to the LSU AgCenter with a B.S. in biology from the University of Minnesota and experience managing conservation and population genetics projects at UC Davis and in as a BioProcess associate in the Affymetrix Reagent Operations Group. Away from the lab, Emily is an accomplished hand knitting pattern designer, with several published designs. Chris earned a PhD in plant pathology at Cornell and has been teaching and conducting research on sweetpotato diseases for 39 years.

Once they leave the lab, virus-tested tissue cultures are transferred to greenhouses at the LSU AgCenter Sweet Potato Research Station in Chase, LA. The team members there include Tara Smith, station coordinator, Arthur Villordon, Professor and lead scientist, research associates - Theresa Arnold, Cole Gregorie, and Bill McLemore, farm manager - Jimmy Ronsonet and numerous support staff. The team works collectively to manage the greenhouse and field operations, propagating the plants through several stages to eventually produce foundation ‘seed' storage roots as well as greenhouse-grown vine cuttings that are marketed to commercial operations throughout Louisiana, the U.S. and internationally. Arthur earned his PhD from LSU with a concentration in sweetpotato breeding and genetics and has been conducting research on sweetpotato growth and development for over 25 years, most recently establishing procedures for producing sweetpotato plants in an aeroponics system which has greatly enhanced propagation potential and efficiencies in our foundation seed program. Tara works extensively with the sweetpotato industry throughout Louisiana, the United States and abroad.

Educational efforts regarding clean seed and virus infection, directed at our clientele coupled with the advisory process are helping to direct research efforts on station and contributing to the sustainability of the Louisiana industry. Our research support team working at the station has over 60 years of combined technical experience which has contributed to improved efficiencies and operations related to all aspects of the sweetpotato foundation seed program and efforts to produce clean planting material for our industry. The sweetpotato teams' collective technical expertise is complimentary to the end goal, which is producing high quality plant material to service the sweetpotato industry.

As a result of the 2015 Cooperative Agreement Program, USDA-APHIS designated funds for the start-up of the National Clean Plant Network for Sweetpotatoes (NCPN-SP). This annual grant process is made possible by the Farm Bill, which currently budgets $5M to be shared among the seven current specialty crops.  The inaugural meeting of the Tier 2 Governing Body was held in Winnsboro, LA in conjunction with an LSU AgCenter field day in August.  NCPN-SP held a workshop hosted by Dr. Jorge Abad and staff of the USDA-APHIS Plant Germplasm Quarantine Program in Beltsville, Maryland in September 2015.  Representatives from each of six sweetpotato centers as well as from USDA labs were able to see cutting-edge facilities and programs for virus detection and elimination for sweetpotato.  The group developed the first target list of viruses for sweet potato and agreed on protocols for indexing for these viruses that will be followed in each center.\ 

For more information contact Dianne Coats dianne_coats@ncsu.edu