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William M. Walter Jr.

The sugar content of five sweetpotato [Ipomoea batatas (L.) Lam.] cultivars (`Centennial', `Cordner', `Georgia Red', `Jewel', and `Sweet Red') was measured by high-performance liquid chromatography (HPLC) and compared to the sugar content of the cellular sap measured by refractive index (RI). The HPLC and RI sugar contents were measured at harvest, after curing, and during storage. Changes in the sugar content, as determined by the RI, were found to be linearly related to changes in the sugar content of cell sap and tissue, as measured by HPLC, indicating that this method can be used to monitor changes in postharvest total sugar content.

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Melvin R. Hall

Sweetpotato [Ipomoea batatas (L.)] storage root yields were evaluated from ≈ 25-cm transplants. The shoot apex was either removed or not removed from pulled (underground stem retained) and cut (underground stem removed) `Georgia Jet' and `Red Jewel' plants. The shoot apex was not removed from pulled and cut `Jewel' plants on which the basal half was immersed or not immersed in calcium hypochlorite solutions. Cut plants of all three cultivars produced higher total marketable and U.S. no. 1 yields than pulled plants. However, neither removing the shoot apex from `Georgia Jet' and `Red Jewel' nor immersing the basal half of `Jewel' plants in calcium hypochlorite solutions improved yields.

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P.J. Grant, J.Y. Lu, D.G. Mortley, P.A. Loretan, C.K. Bonsi and W.A. Hill

The sweetpotato [Ipomoea batatas (L.) Lam] breeding clone TU-82-155 was grown during Spring 1990 and Summer 1991 in standard Tuskegee Univ. (Alabama) growth channels (0.15 × 0.15 × 1.2 m) for 120 days in a greenhouse using a hydroponic (nutrient film) system with a modified half-strength Hoagland nutrient solution. The nutrient solution was changed every 2, 14, or 28 days. Total N, oil, ash, amino acid, vitamin, and mineral concentrations in storage roots generally were higher and dry weight and starch concentration were lower with 2-day solution changes than with those less frequent.

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Petra Wolters, Wanda Collins and J.W. Moyer

The establishment of a sweet potato repository in Georgia that will eventually accept and distribute true seed of sweet potato [Ipomoea batatas (L.) Lam.] raised the question of seed transmission of viruses, especially of sweet potato feathery mottle virus (SPFMV). Seedlings obtained from virus-infected parent plants were free of viral infection. Examination of virus distribution in virus-infected plants determined that SPFMV was present in vegetative tissue, but not in reproductive organs, indicating that the probability of SPFMV transmission in sweet potato through seed is very low.

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Wesseh J. Wollo and Rufus Jones

The impacts of unloaded quantity, disposable personal income, retail price index of fresh potatoes (Solanum tuberosum L.), and seasonal monthly variables on sweetpotato [Ipomoea batatas (L.) Lam.] price in the St. Louis and Chicago terminal markets were estimated using a regression analysis technique. These markets can absorb a modest increase in sweetpotato quantity without a decrease in wholesale price, but a significant increase in quantity would decrease wholesale price. Sweetpotato price is higher during October, November, and December than in September; therefore, producers must give attention to marketing sweetpotatoes during these months. Also, increased shipments of sweetpotatoes to these markets should not be considered in anticipation of an increase in disposable income.

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Howard F. Harrison Jr. and Philip D. Dukes

Four sweetpotato [Ipomoea batatas (L.) Lam.] clones were evaluated for metribuzin tolerance in greenhouse and field experiments. W-262 exhibited metribuzin response similar to the highly tolerant clone Tinian (U.S.P.I. 153655). SC 1149-19 was highly sensitive to metribuzin, and the commercial cultivar Jewel was intermediate in tolerance. Due to its more desirable horticultural characteristics and higher yields, W-262 is superior to Tinian as a source of metribuzin tolerance in sweetpotato breeding. Chemical name used: 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one (metribuzin).

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R.L. Jarret, G. Lovell and M. Spinks

The S-9 Plant Germplasm Collection maintains and distributes germplasm of various horticultural crops, including pepper (Capsicum spp.), watermelon (Citrullus lanatus), okra (Abelmoschus spp.), eggplant (Solanum melongena), miscellaneous Solanum spp., sweetpotato (Ipomoea batatas spp.), luffa (Luffa spp.), gourds (Lagenaria and Momordica spp.), squash (Curcurbita moschata), pumpkin (Curcurbita maxima), marigold (Tagetes spp.), Stokes' aster (Stokesia laevis), hibiscus (Hibiscus spp.), Engelman daisy (Engelmannia pinnatifolia), pampasgrass (Cortaderia selloana), ornamental bamboo (Bambusa spp.), and other ornamental grasses. Seed or other propagules of these plant materials are available for research purposes. Detailed information on individual collections and general information on the USDA National Plant Germplasm System will be presented.

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Elisa Mihovilovich, Humberto A. Mendoza and Luis F. Salazar

Combining ability for resistance to Sweetpotato Feathery Mottle Virus (SPFMV) was evaluated in seven sweetpotato [Ipomoea batatas (L.) Lam] clones. A diallel mating design was used, which resulted in 16 full-sib families. Families were evaluated for SPFMV resistance under greenhouse conditions in a randomized complete-block design. Resistance was tested by grafting Ipomoea nil `Scarlet O' Hara' infected with the russet crack strain of SPFMV (RC-SPFMV) onto individual plants of the families being evaluated. Symptomless plants were further indexed by cleft grafting virus-free Ipomoea setosa Ker plants onto the tested plants. Those plants in which the virus was not recovered by this test were considered resistant. Analysis of variance for SPFMV resistance revealed significant general combining abilities (GCA). Two clones, DLP-886 and TN90.300, exhibited significant positive GCA for SPFMV resistance. No significant specific combining abilities (SCA) were detected among the crosses. Breeding for resistance to SPFMV should focus on careful selection of resistant parents. In addition, results suggest that additive gene action is important in resistance to SPFMV.

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A.Q. Villordon, J.M. Cannon, H.L. Carroll, J.W. Franklin, C.A. Clark and D.R. LaBonte

Yield tests and evaluation of selected storage root and vine characters were conducted among 12 `Beauregard' sweetpotato [Ipomoea batatas (L.) Lam.] mericlones. Maximum yield differences were 43%, 48%, 79%, and 40% for U.S. #1, canners, jumbos, and total marketable yield, respectively. Additive main effect and multiplicative interaction (AMMI) biplot analysis was useful in graphically presenting the yield differences and stability patterns of mericlones. Differences were also detected in vine length, internode diameter, and internode length. Digital image analysis of U.S. #1 storage roots also revealed differences in storage root minor axis length, roundness, and elongation attributes. The results provide valuable information for enhancing current methods of evaluation and selection of mericlones for inclusion in sweetpotato foundation seed programs.

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Mwamburi Mcharo*, Don Labonte, Chris Clark and Mary Hoy

Using two sweetpotato (Ipomoea batatas (L.) Lam) F1 populations from diverse environments we investigated the AFLP marker profiles of the genotypes for association studies between the molecular markers and southern root-knot nematode (Meloidogyne incognita) resistance expression. Population one consisted of 51 half-sib genotypes developed at the Louisiana State Univ. AgCenter. The second population consisted of 51 full-sibs developed by the East African and International Potato Center sweetpotato breeding programs. Results for nematode resistance expression indicate a binomial distribution among the genotypes. Using analysis of molecular variance, logistic regression and discriminant analysis, AFLP markers that are most influential with respect to the phenotypic trait expression were selected for both populations. A comparative analysis of the power of models from the two statistical models for southern root-knot nematode resistance class prediction was also done. The diversity and possible universal similarity of influential markers between the two populations and the expected impact in sweetpotato breeding programs will be discussed.