Donald R. La Bonte and Tara P. Smith

The sweet potato, which has grown to be Louisiana’s most popular vegetable, had its beginnings as a commercial crop in the early 1900s, when commercial sweet potato districts in the United States were developed along geographic lines to serve local needs. The first commercial sweet potato district in Louisiana originated near Sunset in St. Landry Parish around 1910.

During the 1920s and 1930s, consumers became increasingly aware of the nutritional qualities of sweet potatoes. About the same time, the Louisiana Agricultural Experiment Station released the Unit 1 Porto Rico, developed by Julian C. Miller. This new variety – which had an attractive skin and a moist, orange flesh high in vitamin A content – catapulted Louisiana into a national and international marketing campaign. As demand for orange, moist-flesh sweet potatoes increased, Louisiana producers were able to compete in more markets across the United States, many of which had traditionally been dominated by drier, white-fleshed sweet potato varieties.

The Louisiana industry coined the term “yam” in 1937 as part of a national marketing campaign to differentiate its product from the drier, white-fleshed types being grown on the East Coast. Eventually, the industry spread north into Avoyelles Parish in an effort to mitigate damage caused by the sweetpotato weevil. By the 1960s, the Oak Grove commercial district located in northeast Louisiana and the St. Francisville district in southeast Louisiana had also grown to considerable size. During the late 1980s following the release of the Beauregard variety, resurgence in acreage occurred along the Macon Ridge in north Louisiana. West Carroll, Morehouse, Richland and Franklin parishes in northeast Louisiana quickly became the largest production area in the state. In 1999, approximately 25,000 acres of sweet potatoes were produced in Louisiana. Present-day commercial production is concentrated in northeast Louisiana in Franklin, Richland, West Carroll and Morehouse parishes, in central Louisiana in Avoyelles and Rapides parishes and in southwest Louisiana in St. Landry, Evangeline and Acadia parishes.

Popularity of sweet potatoes soared during the years following the Great Depression. Sweet potatoes were considered a subsistence crop during this time and were grown not only commercially but in home gardens. Inputs such as fertilizer were rarely used because of costs, thus yields realized in many cases were marginal. Acreage in Louisiana’s peaked in 1935 at 123,000 acres. During that same year, U.S. acreage approached 1 million acres. Over the next several decades, sweet potato acreage decreased, transitioning into a specialty crop industry. Louisiana acreage has averaged about 14,000 over the past five years, while acreage in the United States in 2011 approached 134,000.

Research and Development

The development of today’s high-yielding, delicious sweet potato varieties began in Louisiana more than 70 years ago. Julian C. Miller and others at the Louisiana Agricultural Experiment Station discovered how to induce flowering and seed set by trellising sweetpotato vines onto fences. They found that this straightforward technique stressed the plant and caused it to flower. This created a world of opportunity to develop new varieties for the industry by genetic recombination. A fast-paced effort ensued to collect sweet potato varieties from throughout the world and to make as many crosses between them as possible. Many of the varieties resisted flowering, and just a handful of seed was produced. Ever so slowly, however, new varieties arose to replace the varieties from the Caribbean, which had little or no disease resistance, poor and erratic yield, and a muted orange flesh.

Seventy years later LSU AgCenter researchers are still at it. Scientists including Miller, Travis and Teme Hernandez, Larry Rolston and Don La Bonte have left of legacy of sweet potato variety development. The scientists and their creations are as follows:

Julian C. Miller – Unit 1 Porto Rico, Acadian, Centennial, Earlyport, Goldrush, Heartogold, Pelican Processor, Queen Mary, Ranger, Lakan and Julian

Travis Hernandez and Teme Hernandez – Jasper, Eureka and Travis

Larry Rolston – Darby and Beauregard

Don La Bonte – Hernandez, Bienville, 96-117, Evangeline, Murasaki-29, Bonita, 05-111, 07-146

From Unit 1 Porto Rico to Beauregard to varieties slated for release in 2012 – LA 05-111 and LA 07-146 – sweet potato varieties released by the LSU AgCenter have improved not only the Louisiana sweet potato industry but sweet potato production around the world. Today’s researchers still use the nursery started by Miller years ago on the LSU campus in Baton Rouge. The breeding program builds on a legacy of methodical progress toward developing the perfect sweet potato.

Sweet Potato Diseases

Wes Martin, LSU AgCenter sweet potato plant pathologist, made several important discoveries that helped the sweet potato industry manage disease and produce healthy crops. He was the first to discover the causal organisms associated with soil rot – a disease that almost decimated the U.S. sweet potato industry – and circular spot. In addition, he was a key member of the team of plant pathologists who identified the cause of bacterial soft rot. Martin actively cooperated with the sweet potato breeding program and developed methods to screen for disease resistance still used today.

Martin was involved in development of several sweet potato varieties including Centennial, Eureka, Jasper, Julian and Travis. Because of Martin’s efforts and those, more recently of Chris Clark, diseases which once were the scourge of the industry – fusarium wilt, soil rot and russet crack – are no longer an issue. New varieties now are bred for disease resistance.

Pest Management

Several LSU AgCenter scientists have contributed valuable information over the years related to sweet potato pest management. Entomologists have conducted research on how insects affect sweet potatoes and have developed management strategies for these insects. Soil insects such as the sweetpotato weevil, white grubs, cucumber beetles, wireworms and the sugarcane beetle have all threatened the industry. Many of these insects, such as the sweetpotato weevil, are now effectively managed because of the efforts of scientists such as Larry Rolston, Jack Bagent, Abner Hammond and Rick Story.

Hammond played a key role in developing and testing the synthetic pheromone for the sweetpotato weevil. The pheromone is used in all sweet potato production regions around the world to monitor sweetpotato weevil populations. A comprehensive integrated pest management program for the sweetpotato weevil was implemented in Louisiana, and the industry no longer views this insect as a limiting factor to their sweet potato operations.

LSU AgCenter scientists also develop strategies for controlling weeds in sweet potato production. They screen and evaluate herbicides giving producers the tools they need to manage many problematic weed species.

Sweet Potato Research Station

In 1948, Miller brought to fruition his idea of a separate research station just for sweet potato research. The 308-acre Sweet Potato Research Station was established in Chase, La., through a direct appropriation of the Louisiana legislature. The station’s mission was to produce top-quality planting stock to serve the commercial sweet potato industry in Louisiana and also to conduct research in various disciplines to enhance production.

Foundation Seed Program

In 1949, the first foundation seed was planted at the station. Approximately 20 roots each of Porto Rico, Goldrush, Earlyport, Pelican Processor and Whitestar were fumigated with methyl bromide in Baton Rouge by the Louisiana State Department of Agriculture. These roots were transported to Monroe, La., and bedded in a greenhouse in the early spring of 1949. The sprouts from these roots were brought to the research station and established for foundation seed production. This material formed the nucleus from which the foundation seed program was developed.

In 1999, the foundation seed program was converted to a virus-tested program. Virus-tested tissue culture plants are produced by a process termed meristem-tip culture. The plants are then increased each year by the LSU AgCenter and Certis USA, a private company that increases the tissue cultures trough nodal propagation techniques. All dominant commercial varieties grown in Louisiana are represented and increased in the foundation seed program.

The LSU AgCenter sweet potato foundation seed program has long served the Louisiana sweet potato industry by providing high quality seed to commercial producers. The seed is from sweet potatoes free of obvious mutations or other defects, with a uniform skin, good color and shape, and devoid of major insect damage. Foundation seed is available for all commercial producers and home gardeners in the state. In addition to satisfying in-state needs, the station also supplies seed to out of state producers, if supply is available. In 2007, the station began working with domestic and international entities to supply transplants for propagating purposes.

Research Station

The LSU AgCenter Sweet Potato Research Station is the only research station in the United States solely devoted to sweet potato research and development. Since its establishment, the station has remained the hub through which sweet potato research and outreach efforts are delivered to the industry and public at large. Numerous scientists have directed the research efforts at the station, including Teme Hernandez, Travis Hernandez, Harrell Hammett, Ron Robbins, Larry Rogers, Richard Parish, Bill Mulkey, Mike Cannon, Arthur Villordon, Robert Hutchinson and presently Tara Smith.

The Sweet Potato Research Station focuses on foundation seed production, improving production efficiency, sweet potato breeding, pest management and understanding more about viruses and diseases that limit productivity. In 2009, the LSU AgCenter along with Mississippi State University, North Carolina State University and University of California at Davis received a $2.8 million grant from the U.S. Department of Agriculture Specialty Crop Research Initiative program, which focuses on improving production efficiency and quality in the sweet potato production system. As part of this project, a prototype production model developed by Villordon is validated on farms across the United States. The goal of these efforts is to develop production models and a decision support system that will aid producers in making informed production decisions concerning their crop, which will ultimately contribute to a more sustainable production system.

Historically, the faculty and the staff at the sweet potato research station have contributed valuable information related to cultural practices and various aspects of sweet potato production including plant quality, spacing, irrigation and fertility.

The Future

An increasingly health-conscious public, combined with value-added product diversity, have brought the once lowly sweet potato to a respected and reserved place on everyday menus. In addition to the fresh market sector, the processing sector has become increasingly invested in sweet potatoes. ConAgra Lamb Weston opened a state-of-the-art processing facility near Delhi, La., in 2010, devoted to processing frozen sweet potato products. Producers are beginning to entertain the idea that they can make a sizable return simply by supplying the processing industry with sweet potatoes as an adjunct to their domestic fresh market and growing export business.

The Louisiana sweet potato industry has experienced both prosperous and trying times throughout history. Weather-related disasters, insect outbreaks, disease issues, struggling markets and variety decline have all threatened the integrity of the industry at various times in the past. However, the industry has always prevailed. Sustaining the industry along the way was the research and outreach efforts of the LSU AgCenter.

Donald R. La Bonte, Professor, School of Plant, Environmental and Soil Sciences, LSU AgCenter,
Baton Rouge, La.  and Tara P. Smith, Extension Sweet Potato Specialist, Sweet Potato Research Station, LSU AgCenter, Chase, La.

(A shorter version of this article was published in the spring 2012 issue of Louisiana Agriculture.)