846 J. AMER. SOC. HORT. SCI. 128(6):846–855. 2003. J. AMER. SOC. HORT. SCI. 128(6):846–855. 2003. Cultivar Decline in Sweetpotato: I. Impact of Micropropagation on Yield, Storage Root Quality, and Virus Incidence in ‘Beauregard A.D. Bryan Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695 Z. Pesic-VanEsbroeck Department of Plant Pathology, North Carolina State University, Raleigh, NC 27695 J.R. Schultheis and K.V. Pecota Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695 W.H. Swallow Department of Statistics, North Carolina State University, Raleigh, NC 27695 G.C.Yencho 1 Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695 ADDITIONAL INDEX WORDS. Ipomoea batatas, meristem-tip culture, clonal degradation, genetic drift, Sweet potato feathery mottle virus ABSTRACT. Decline in sweetpotato yield and storage root quality has been attributed to the accumulation of viruses, pathogens and mutations. To document the effects of decline on yield and storage root quality, two micropropagated, virus-indexed, greenhouse produced G1 ‘Beauregard meristem-tip cultured clones, B94-14 and B94-34, were compared with 1) micropropagated B94-14 and B94-34 clones propagated adventitiously up to five years in the field (G2, G3, G4, G5); and 2) nonmicropropagated, unimproved stock of ‘Beauregard seed in field trials during 1997 to 2001. At least three trials were located each year in sweetpotato producing regions in North Carolina. In 2000 and 2001, two trials were monitored weekly for foliar symptoms of Sweet potato feathery mottle virus (SPFMV) and other potyviruses, and virus-indexed for selected viruses using Ipomoea setosa and nitrocellulose enzyme linked immunosorbant assays (NCM- ELISA). Only SPFMV was detected in field samples using NCM-ELISA, but this does not rule out the presence of newly described viruses infecting sweetpotato for which tests were unavailable. Monitoring indicated that all G1 plants became infected with SPFMV by the end of the growing season, and that G2 to G5 plants were probably infected in their initial growing season. G1 plants consistently produced higher total yield, total marketable yield (TMY), U.S. No. 1 root yield and percent No. 1 yield than G2 to G5 plants. G1 plants also produced storage roots with more uniform shapes and better overall appearance than storage roots produced from G2 to G5 plants. Also, G2 to G5 storage roots tended to be longer than G1 storage roots. Rank mean yield and storage root quality measurements of each location were consistent with means averaged over locations per year and suggested a decrease in yield and storage root quality with successive seasons of adventitious propagation. Linear regression analysis used to model yield and storage root quality measurements of seed generations G1 to G5 indicated that total yield, TMY, No. 1 yield, percent No. 1 yield, shape uniformity, and overall appearance decreased gradually, and that length/diameter ratios increased gradually with generation. The rate of decline in No. 1 yield was greater for B94-34 compared to B94-14. Both viruses and mutations of adventitious sprouts arising from storage roots probably contribute to cultivar decline in sweetpotato, but further studies are needed to determine their relative importance. A simple profitability analysis for G1 vs. G2-G4 planting material conducted to facilitate better understanding of the economics of using micropropagated planting material to produce a crop in North Carolina revealed that growers have a potential net return of $2203/ha for G1 plants, $5030/ha for G2 plants, and $4394/ha for G5 plants. Thus, while G1 plants generally produce higher No. 1 yields, a greater monetary return can be achieved using G2 plant- ing materials because of the high costs associated with producing G1 plants. Based on this analysis, the best returns are accrued when growers plant their crop using G2 and/or G3 seed. Sweetpotato can be propagated asexually via roots or stems. In the United States, growers multiply sweetpotatoes asexually by saving a portion of the year s crop as seed roots. In early spring, the seed storage roots are planted in beds, and adventitious sprouts arising from these roots are cut and transplanted to the field to produce the next crop. After several years of adventitious propa- gation via storage roots, yield and root quality are often reduced. The reduction of storage root quality and yield in sweetpotato, referred to as cultivar running-out (Miller et al., 1959) or decline has been attributed to the accumulation of viruses, pathogens and mutations (Clark et al., 2002; Villordon and La Bonte, 1995). Mutations in sweetpotato induce color changes in the root epi- Received for publication 8 Jan. 2003. Accepted for Publication 2 June 2003. This paper is a portion of a thesis submitted by Adrienne D. Bryan. The research was supported by the N.C. Agricultural Foundation, the N.C. Crop Improvement As- sociation, the N.C. Sweetpotato Commission, and the N.C. Sweetpotato Certified Seed Growers Association. We thank Marilyn Daykin for meristem-tip culture procedures, Lauren Upton and Jennifer Smith for assistance with greenhouse and field work, Charles W. Averreand Dennis Adams for assistance in harvest and evaluations, and Sandy Barnes, Randy Herring and the staff at the Cunningham Research Station, Kinston, NC and the staff at the Horticultural Crops Research Station, Clinton, NC who managed the field tests and assisted with harvest. We also greatly appreciate the cooperation of Extension Associate, Bill Jester, County Agents Billy Little and Milton Parker, and sweetpotato growers George Wooten, Dale Bone, Jerome Vick, Ralph and Sylvia Batchelor, and Sonny Scott. 1 Corresponding author; e-mail Craig_Yencho@ncsu.edu.