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Larry S. Kennedy and Paul G. Thompson

The enzymes alcohol dehydrogenase, diaphorase, esterase, glutamate dehydrogenase, glucosephosphate isomerase, isocitrate dehydrogenase, malate dehydrogenase, malic enzyme, 6-phosphogluconate dehydrogenase, phosphoglucomutase, shikimate dehydrogenase, and xanthine dehydrogenase were analyzed by starch gel electrophoresis of leaf tissue from nine sweetpotato [Ipomoea batatas (L.) Lam.] cultivars. Bands of most enzymes were well-defined. Polymorphisms were found in nine enzymes, and cultivars were identified by comparing polymorphisms.

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Wesseh J. Wollo

A market window technique was used to evaluate the market potential for sweetpotato [Ipomoea batatas (L.) Lam.] production in southeastern Missouri. Weekly prices were averaged over 5 years in real terms and were used to identify market windows in St. Louis and Chicago. The results indicate that sweetpotatoes may be a profitable production alternative in southeastern Missouri.

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Joshua K. Craver, Chad T. Miller, Kimberly A. Williams and Daniel L. Boyle

result of chemical stimulation Missouri Bot. Garden Annu. Rpt. 16 125 148 Trotter, A. 1904 Intumeszenze fogliari di “Ipomoea batatas.” Ann. Bot. (Lond.) 1 362 364 Wallace, R.H. 1928 Histogenesis of intumescences in the apple induced by ethylene gas Amer

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J.R. Bohac and S. Rajapakse

An Ipomoea accession from Indonesia, originally classified as I. trifida, was found to segregate in flower morphology. It was hypothesized to be either a very close relative of I. batatas (6x sweetpotato), or a hybrid between I. batatas (6x) and I. trifida (2x). Twelve seedlings of this accession were grown and precise measurements of sepal angle, corolla shape, and root morphology were taken. Samples were also compared on the DNA level using molecular markers. Based on morphological measurements, it was found that some individual seedlings of the unknown Ipomoea accession were not significantly different than I. batatas; others were not significantly different than I. trifida. The control I. batatas and I. trifida lines were significantly different from each other. DNA flow cytometry was used to determine that all seedlings were diploids with the same amount of DNA per cell. Overall plant morphology and molecular analysis confirmed that all of the seedlings were very closely related and the segregation in flower morphology was not due to a seed mixture. This data is consistent with the hypothesis that the accession is a hybrid between I. batatas and I. trifida.

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Lavetta Newell, Tonda Bardwell and James O. Garner Jr.

In two experiments, 16 sweet potato genotypes (Ipomoea batatas L.) were evaluated for drought tolerance using the detached - leaf water loss method as reported by Walker and Miller (1986). Dry weight loss was also determined. Differences in the rate of leaf water loss over a 48 hour period were found.

Vardaman had the greatest amount of dry matter loss and the lowest level of water loss. However, no relationship between dry matter loss and water loss was found.

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Dapeng Zhang, Wanda W. Collins and Suzanne Belding

Eight sweetpotato [Ipomoea batatas (L.) Lam.] clones were evaluated for the digestibility of their starch in animals with a simple in vitro screening method. Starch digestibility varied significantly among clones. After dry-heat treatment at 100C for 30 minutes, digestibility of the most heat-sensitive clone increased only 37.8%. Excellent repeatable results were obtained with a simple weight-loss method. This assay procedure can be used as a screening method in breeding digestible sweetpotatoes for animal feed.

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W.A. Mulkey and J.H. Hernandez

Foundation sweetpotato [Ipomoea batatas (L.) Lam] seedstock has been produced annually at the Sweet Potato Research Station since 1949. Breeder seedstock is selected from superior hills and used for the following year's foundation seedstock. Fields are intensely monitored after planting until harvest to remove off-type plants, mutations, etc. Seedstock is harvested from August through October, stored, graded, and repacked beginning in late January, and then made available to the growers during the early spring.

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James M. Dangler

Transparent polyethylene is used to enhance sweetpotato [Ipomoea batatas (L.) Lam.] transplant production in hotbeds and unheated field beds. Black plastic is used also in unheated field beds. The use of these bed covers, however, frequently results in transplant damage due to overheating. Despite the positive results obtained by using rowcovers in sweetpotato transplant production, recommendations for their use are not included in extension publications. Successful adoption of rowcovers by sweetpotato transplant producers in Alabama is illustrated.

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Peggy Ozias-Akins and Robert L. Jarret

The nuclear DNA content of 53 accessions from 24 Ipomoea (Convolvulaceae) species, including four sweetpotato cultivars, was determined by flow cytometry of DAPI-stained nuclei. Ploidy level and DNA content were significantly correlated within the genus, but more highly so within species that contained multiple cytotypes. DNA content of cultivated Z. batatas (L.) Lam. (4.8 to 5.3 pg/2C nucleus) and feral tetraploid I. batatas (3.0 to 3.5 pg/2C nucleus) was estimated from the known DNA content of chicken erythrocytes (2.33 pg), which were used as an internal standard. Tetraploid forms of Z. cordato-triloba Dennstedt also were identified. Ploidy analysis using flow cytometry is rapid and suitable for large-scale experiments such as studying the genetic structure of populations of Z. batatas and related species. Chemical name used: 4′,6-diamidino-2-phenylindole (DAPI).

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G. S. Varadarajan and C. S. Prakash

The sweet potato (Ipomoea batatas) and its relatives (the batatas complex) appear to have evolved in the New World and radiated over several geographic centers in the tropics and subtropics. Traditional studies on taxonomy, cytogenetics, and reproductive biology of the batatas complex have enabled us to investigate certain evolutionary aspects. We conclude that this complex is a monophytetic, “polyploid pillar”, evolved by chromosome doubling (euploidy) and interspecific hybridization. We apply molecular genetic techniques to detect variation [restriction fragment length polymorphism (RFLP) and DNA fingerprinting analyses] to reexamine some of the evolutionary issues that could not be satisfactorily addressed by the conventional approaches, e. g., phylogenetic history of the batatas group, the diploid ancestors of the polyploid members, homology/diversity of genome(s) within the entire group. We find DNA variation in the hypervariable or multiple copy regions of the genome in Ipomoea species. In addition, we are investigating polymorphism in unique/low copy regions using a battery of DNA sequences from homologous as well as heterologous sources. The success of this study will hopefully shed a new light on the subject of evolutionary biology and may also have potential applications in the sweet potato breeding.