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Jonathan R. Schultheis, Wanda W. Collins and Charles W. Averre

Micropropagated sweetpotato is utilized in California as pan of its seed production program. Sweetpotato yields and quality might be improved in North Carolina by incorporating micropropagation as pan of its plant production scheme. Field studies were conducted in 1992 and 1993 to determine the effects of micropropagation, virus, and hill selection on yield and qualify of Jewel and Beauregard varieties. In 1992, yield was increased in Beauregard with micropropagated plants compared with plants that were derived from the North Carolina seed program. However, no yield advantage was measured when Jewel was micropropagated. In 1993, yield from micropropagated Beauregard sweetpotato plants was the same as when plant material was derived from the North Carolina Certified Seed program. Virus-free micropropagated Beauregard plants yielded more number one and canner grade roots than micropropagated plants that harbored the virus at planting. Russet crack symptoms were significantly greater in roots that were not micropropagated compared with micropropagated plants. Total marketable yield of Jewel was increased when obtained from micropropagated versus nonmicropropagated plant stock. Micropropagated Jewel obtained from a California selection yielded nearly 20% less than the North Carolina selection. Yields from micropropagated planting stocks consistently were equal to or better (typically 10 to 20%) than from plant stock not micropropagated.

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Jonathan R. Schultheis, W.R. Jester and Charles W. Averre

Sweetpotato yield and quality are influenced by a N fertilization program. These studies were conducted to evaluate the effect that different N rates and application times had on the yield and quality of Beauregard roots. Three experiments were conducted in separate locations in North Carolina: One in 1992 to evaluate N rates of 28 to 56 kg·ha–1; and two in 1994 that evaluated nitrogen rate and time of N application. In 1994, N timing using single applications (21, 28, and 35 days after planting) were compared with split applications (10–21 and 21–35 days after planting). Also, in 1994, N rates for the season was varied from 0 to 42 kg·ha–1 comparing single and split applications. No yield differences were detected when N rate was varied from 14 to 56 kg·ha–1. However, the application of at least 14 kg N/ha increased yield when compared with the control (0 kg N/ha). The highest yield of US #1 marketable roots was obtained when all N was applied at 21, 28, or 35 days compared with split applications made at 10 and 21 days after planting. Roots tended to be shorter with single vs. split N applications.

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W. R.(Bill) Jester, Charles W. Averre and Jonathan R. Schultheis

Russet crack-like symptoms have been observed with increasing frequency on Beauregard storage roots in North Carolina and resulted in some crop failures in neighboring states. The objective of this experiment was to determine if this cracking disorder was soil-borne, seed transmissible or transmissible via grafting. Beauregard plants were obtained from cuttings from commercially available virus-indexed micropropagated plants (M), and selected symptomatic roots (culls) originating from 1992 Foundation stocks (R). In a third treatment plants from each source were alternated in a row, then M and R plants were cleft grafted. The planting was made June 30, 1993 and replicated five times (12 plants per rep). Yield was determined and roots from each hill were washed and examined for russet crack-like symptom(s), and interior color on the proximal end. M roots had 82% good color; while R roots had 19%. M plants contained 0.3% symptomatic roots; R plants 65.5%. Similarly, only 1.6% of the M plants contained a symptomatic root, while 95.0% of the R plants had symptomatic roots. One-third of the grafted M plants contained one or more roots with cracking symptoms. M outyielded R. The russet crack-like disorder was determined to not be soil-borne, but was transmissible through the seed or grafting.

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Jonathan R. Schultheis, Carroll E. Collins and Charles W. Averre

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Wilfred R. “Bill” Jester III, Jonathan R. Schultheis and Charles W. Averre

Sweetpotato varieties differ in their ability to efficiently use N. This study was conducted to determine if time of N application affected root yield and quality in the variety Beauregard. Nitrogen sidedress single-application treatments were applied at 10, 21, 28, and 35 days after transplanting. Two split application treatments were evaluated: l) 44.8 kg N/ha were applied 10 days after transplanting and 22.4 kg N/ha applied 21 days after transplanting and 2) 33.6 kg N/ha were applied 21 and 35 days after transplanting. The N source was calcium nitrate (15.5–0–0) and totaled 67.3 kg N/ha for all treatments. Plots were four rows and 6 m long, and treatments were randomized in five blocks. Harvested roots were sorted according to U.S. Dept. of Agriculture grading standards and weighed. Highest yields of U.S. no. 1 grade roots were obtained by applying N 21 to 35 days after transplanting. Total marketable yield was highest when application was made at 28 or 35 days after transplanting. Root length, at the 10% level of significance, was shorter when one vs. two N applications were applied. Using one N application compared with two N applications seems to be beneficial as shown by increased total marketable yields and yield of U.S. no. 1 roots and reduced root length.