With farmers in dire need of something to generate bank deposits after tobacco’s lean years and the damage from the 1999 hurricane season, micropropagated sweetpotatoes just might be the crop to boost cash flow in years to come.
The sweetpotato, North Carolina’s official vegetable, brought in $60 million in cash receipts last year from the more than 37,000 acres grown on the western edge of our state’s coastal plains, home to much of the nation’s crop.
Due mostly to seed stock improved by the College of Agriculture and Life Sciences’ Micropropagation Unit (MPU) at N.C. State University, a total of about 40,000 coastal plains acres probably will go to sweetpotatoes this year, says Dr. Zvezdana Pesic-van Esbroeck, MPU director.
Micropropagation is the carefully controlled generation of plants from a few cells of an original plant, which allows massive plant regeneration from originals that have been checked for disease and other problems.
The MPU meets the increasing demands of North Carolina’s fruit and vegetable industries for pathogen-free, virus-indexed, true-to-variety, asexually propagated stock plants.
N.C. State researchers, Cooperative Extension specialists and county agents, who in 1988 introduced the first micropropagated sweetpotatoes into North Carolina fields, strive to hold and improve the plant’s national market share. That share already is a healthy 40 percent, say statistics from the North Carolina Sweetpotato Commission Inc.
To produce micropropagated plants, researchers such as Pesic-van Esbroeck and Dr. Marilyn Daykin, a tissue culture specialist, grow tiny groups of meri-stematic cells — located at the leading edge of the plant’s growth — under controlled laboratory conditions at the MPU, generating small plants called mericlones.
Mericlone production in the lab bears no relation to the process that creates transgenic, or genetically modified, organisms.
"No sweetpotato mericlone genes are altered or transferred from one plant to another," Pesic-van Esbroeck says.
Researchers check the clones, and pathogen-free mericlones are multiplied — "increased," in growers’ language —through in-vitro techniques.
Later, scientists make cuttings to further increase the mericlones in isolated, insect-free greenhouses at the Sandhills Research Station in Montgomery County.
The MPU’s sweetpotato research is part of a continuing College effort to assist growers. College departments such as Plant Pathology, Horticultural Science and Entomology have cooperated with Extension and growers to help the sweetpotato buck stiff competition from other states.
Extension workers and researchers also help protect the crop from diseases such as the russet crack strain of the feathery mottle virus and against genetic drift, which happens if several generations of the same mother plant’s roots — not the preferred vines — are used for seed stock and replanted in the same field.
"The MPU avoids that problem through cloning the sweetpotato’s vine at the spot where it’s growing, the meri-stem," says Pesic-van Esbroeck. "A virus and other plant pathogens can be present everywhere in an infected plant but only rarely in the meristematic tissue."
Since the cleanest stock comes directly from the MPU, North Carolina Foundation Seed Producer growers must refresh their stock from the N.C. State greenhouse annually. Only that stock guarantees commercial sweet-
The field is yet another place where researchers exercise quality control. Breeders Dr. Craig Yencho of the Vernon James Research and Extension Center in Plymouth, Kenneth Pecota of the College’s Horticultural Science Department, growers and others walk through harvested plantings yearly, while roots still are attached. They examine hundreds of plants, looking for the best. They also evaluate the lab’s existing mericlones in several fields to test for evidence of disease and genetic drift.
Dr. Charles Averre, a retired plant pathologist, helped develop the micropropagation system at N.C. State.
Averre; Dr. Robert Milholland, retired plant pathology professor; Dr. Jonathan Schultheis, Extension horticulture specialist; and Bill Jester, an Extension area specialist, developed and demonstrated micropropagation procedures compatible with existing North Carolina Foundation and Certificate programs. These procedures ensured that sweetpotatoes stayed disease-free and stopped genetic drifts.
"But the most important thing about this program," says Averre, "is to give our growers quality roots. Then they will have a comparative edge, and that’s what pays off."