Sweetpotato is gaining increasing importance in the United States as the health-conscious consumers and the availability of value-added processed products have increased demand. Per capita consumption of the crop increased over 24% from 1998 to 2008, and the value of the U.S. crop in 2009 exceeded $400 million [Lucier and Dettman, 2008; U.S. Department of Agriculture (USDA), 2010]. In 2009, 19.6 million cwt of sweetpotatoes were produced on 97,700 acres (USDA, 2010). However, the cost of production is high, requiring that growers optimize production and quality (Hinson and Boudreaux, 2009; Stoddard et al., 2006).
Since sweetpotato is vegetatively propagated, systemic pathogens, especially viruses, can accumulate in the propagative material, leading to decline in the performance of cultivars (Bryan et al., 2003a, 2003b; Clark et al., 2002). Estimates suggest that yields of the cultivar Beauregard can be reduced by as much as 25% to 40% (Bryan et al., 2003a, 2003b; Carroll et al., 2004; Clark and Hoy, 2006). To counter cultivar decline, major sweetpotato-growing states have developed foundation seed programs that provide “VT” (indexed by grafting to an indicator host, by assaying for specific viruses, or by both and found to be apparently free of known viruses) seed to growers. La Bonte et al. (2004) compared different generations of ‘Beauregard’ produced from small research plots and found increased yields for G2, but not for other generations. However, seed produced from small plots located in large fields of infected material does not represent the same probability for re-infection with viruses as on farms where larger blocks of seed are produced.
The state foundation seed programs all rely on the use of meristem-tip culture and indexing to generate VT tissue culture plantlets, but the methods for subsequent increase and dissemination of clean stock to growers differ from state to state (Dangler, 1994). In Louisiana, VT tissue cultures are increased by nodal propagation and the plantlets are planted in greenhouses at Sweet Potato Research Station, LSU AgCenter, at Chase in December of each year. The plants in the greenhouses are increased by vine cuttings through the winter, and these plants are used as a source of vine cuttings to plant production fields the following summer. The roots harvested from these fields are sold to growers as foundation seed and represent the first generation from the field or G1 seed. Growers, thus, rely on this sole source of G1 seed to begin the seed program on their farms. They produce a G2 crop, which they use the following year for production of their commercial crop. Thus, the commercial crop is usually grown from G2 seed roots, or in some cases, if supplies of G2 are inadequate, also from G3 seed. Bryan et al. (2003a) suggested that in North Carolina, where commercial certified seed growers produce G2 seed for sale to table-stock growers, the greatest net return for sweetpotatoes derives from using G2 plants as the cost for producing G2 plants is much lower than that for producing G1 seed, while the yield and quality remain relatively high. Although growers are encouraged to isolate their seed production from the rest of their commercial production, it is often difficult for them to do this because of the limited availability of land. Management programs for virus vectors have not been developed for sweetpotato in Louisiana (Hammond et al., 2001), and growers have few options for preventing re-infection of their seed. Preliminary evaluations indicated that low incidence of re-infection with viruses can occur during the production of G1 foundation seed. However, there was little information available to evaluate how rapidly seed productivity and quality declined during the increase of seed on farms, where older generations of sweetpotato are also grown and could serve as sources of inoculum for re-infection of new seed. This study was conducted to evaluate changes in quality of seed from different farms in the major sweetpotato production areas of Louisiana to better understand how rapidly seed declines overall and to determine if location of seed production affects decline.
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Bryan, A.D., Schultheis, J.R., Pesic-van Esbroeck, Z. & Yencho, G.C. 2003b Cultivar decline in sweetpotato: II. Impact of virus infection on yield and storage root quality in ‘Beauregard’ and ‘Hernandez’ J. Amer. Soc. Hort. Sci. 128 856 863
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