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Ming Liu, Aijun Zhang, Xiaoguang Chen, Rong Jin, Hongmin Li, and Zhonghou Tang

). Sweetpotato [ Ipomoea batatas (L.) Lam.] is an important human food, animal feed, and industrial raw material, which is grown in more than 100 countries and mainly produced in China ( FAO, 2011 ; Jin, 2012 ). Sweetpotato is a typical “K-favoring” crop ( Tang

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R.L. Jarret, N. Bowen, S. Kresovich, and Z. Liu

Simple sequence repeats (SSRs) were isolated from a size-fractionated genomic DNA library of sweetpotato [Ipomoea batatas (L.) Lam.]. Screening of the library with five oligonucleotide probes, including; (GT)11, (AT)11, (CT)11, (GC)11, and (TAA)8, detected the occurrence of 142 positive colonies among ≈12,000 recombinants. Automated DNA sequencing revealed the presence of simple, compound, perfect, and imperfect SSRs. Five homologous PCR primer pairs were synthesized commercially and used to screen 30 sweetpotato clones for the occurrence of SSR polymorphisms. All primer pairs produced an amplification product of the expected size and detected polymorphisms among the genotypes examined. The potential for the use of SSRs as genetic markers for sweetpotato germplasm characterization is discussed.

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Rozalyn Pama*, Jay Doronila, and Mari Marutani

Fifteen sweetpotato [Ipomoea batatas (L.) Lam] accessions grown on Guam were studied for morphological and genetic characteristics. Accessions, obtained from AVRDC (Asian Vegetable Research and Development Center) in Taiwan, Saipan, Rota, and Guam, were investigated for marketable yield, growth habit and characteristics of tuberous roots (color, shape, sugar content and moisture content). Results of this study were used to determine the morphological relationship of the accessions of sweetpotato. Phenetic analysis revealed four major clusters according to tuberous root characteristics. The genetic relationship of these sweetpotato accessions was also evaluated for genetic differences among accessions. DNA was extracted and went through polymerase chain reaction (PCR). PCR products were analyzed by random amplified polymorphic DNA (RAPD) fingerprinting. Result of the genetic relationship among the sweetpotatoes was compared with the morphology of accessions using UPGMA cluster analysis and principal compounds analysis.

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R.L. Jarret, N. Gawel, and A. Whittemore

Twenty-four accessions of Ipomoea, representing 13 species of section Batatas and the outgroup species I. gracilis and I. pes-caprae were analyzed for restriction fragment length polymorphisms. Polymorphisms were detected by probing Southern blots of restriction enzyme-digested genomic DNA with 20 low or moderate copy number sequences isolated from an I. batatas cv. Georgia Red genomic library. Data were analyzed cladistically and phenetically. Ipomoea trifida, I. tabascana, and collection K233 are, of the materials examined, the most closely related to sweetpotato (I. batatas). Ipomoea littoralis, the only Old World species in the section, is a sister species to I. tiliacea. Ipomoea littoralis, I. umbraticola, I. peruviana, I. cynanchifolia, and I. gracilis are shown to be diploid (2n = 2x = 30). In contrast, I. tabascana is tetraploid (2n = 4x = 60). The intrasectional relationships of section Batatas species and the role of tetraploid related species in the evolution of the cultivated I. batatas are discussed.

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Chana Phromtong and James O. Garner Jr.

Ten day old potted rooted cutting of sweetpotato genotypes `Travis' and MS 21-1 were exposed for seven days to cold (12°C) or 21°C (control) temperatures. Chemical changes that may accompany tolerance or susceptibility to chilling were monitored. No consistent differences in total fatty acid composition were found between the two genotypes. There was an increase in peroxidase (POD) activity of the crude enzyme extract for MS 21-1, the chilling tolerant genotype, when exposed to 12°C for seven days. No differnces were found in POD activity for `Travis', the chilling sensitive genotype. Superoxide dismutase (SOD) and catalase (CA) activity for crude enzyme extracts did not differ between genotypes and was not influenced by storage temperature.

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Abesinghe Arambage, James Garner, and J.L. Silva

Plasmalemma lipid fatty acid changes due to low temperature (12C) were observed in M521-1 and `Travis', chilling-tolerant and -sensitive, respectively, genotypes. Lipid fatty acid changes found in both genotypes after exposure to chilling included decreased palmitic acid (16:0) and an increased unsaturated: saturated fatty acid ratio. Changes detected only in the tolerant genotype were increased linoleic (18:2), linolenic (18:3) and erucic (22:1). Monogalactosyldiglyceride and phosphatidylglycerol were the only lipids with >50% of their fatty acids unsaturated; therefore, it was concluded that these lipids were involved in the chilling tolerance of M521-1. A reduction in arachidonic (20:4) on phosphatidylinositol from `Travis' exposed to 12C resulted in <50% unsaturation of this lipid. This change could be associated with the chilling sensitive response of `Travis'.

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Chana Phromtons and J. O. Garner Jr.

Storage roots of `Beauregard' and Centennial' were analyzed for total fatty acid composition and fatty acid composition by lipid class. The glycolipid, monagalactosyldiglycerol, may have been involved in chilling tolerance of `Beauregard' storage roots. This lipid had over 70 percent low-melting point fatty acids, mostly linoleic acid and linolenic acid. No consistent differences in the composition of phospholipids could be related to the chilling responses of the two sweetpotato cultivars.

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Jyh-Bin Sun, Ray F. Severson, William S. Schlotzhauer, and Stanley J. Kays

Thermal degradation of fractions from sweetpotato roots (`Jewel') was conducted with gas chromatographymass spectrometry to identify precursors of critical flavor volatiles. Upon heating (200 C), sweetpotato root material that was insoluble in methanol and methylene chloride produced similar volatile profiles to those from sweetpotatoes baked conventionally. Volatiles derived via thermal degradation of the nonpolar methylene chloride fraction and the polar methanol fraction did not display chromatographic profiles similar to those from conventionally baked sweetpotatoes. Initial reactions in the formation of critical volatiles appear to occur in the methanol and methylene chloride insoluble components. Maltol (3-hydroxy-2-methyl-4-pyrone) was found to be one of the critical components making up the characteristic aroma of baked sweetpotatoes. Integration of an analytical technique for the measurement of flavor into sweetpotato breeding programs could potentially facilitate the selection of improved and/or unique flavor types.

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Nenita V. Desamero and Billy B. Rhodes

Vitrification, a physiological disorder characteristic of in vitro grown plants, was observed in single-node cultures of sweet potato in mannitol-enriched medium during their second year of storage. Vitrified or vitreous sweet potato plantlets were watersoaked, translucent or glassy in appearance, with thick, swollen, leaves and stems, stunted shoot growth and poor root growth. These plantlets were not able to regenerate normal plants when transferred into fresh regeneration medium nor were they able to survive outside culture conditions.

Electron microscopy revealed changes in the ultrastructures of vitrified sweet potato plantlets. Vitrified plants had defective stomatal complex, starch grain-filled chloroplasts, disrupted cell wall, big air spaces (lacunae), high frequency of cell membrane separation from the cell wall, nuclear disintegration, and cytoplasmic disorganization. These changes in the internal structures of vitrified plants were reflected in their abnormal morphology and physiology.

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Nenita V. Desamero and Billy B. Rhodes

Vitrification, a physiological disorder characteristic of in vitro grown plants, was observed in single-node cultures of sweet potato in mannitol-enriched medium during their second year of storage. Vitrified or vitreous sweet potato plantlets were watersoaked, translucent or glassy in appearance, with thick, swollen, leaves and stems, stunted shoot growth and poor root growth. These plantlets were not able to regenerate normal plants when transferred into fresh regeneration medium nor were they able to survive outside culture conditions.

Electron microscopy revealed changes in the ultrastructures of vitrified sweet potato plantlets. Vitrified plants had defective stomatal complex, starch grain-filled chloroplasts, disrupted cell wall, big air spaces (lacunae), high frequency of cell membrane separation from the cell wall, nuclear disintegration, and cytoplasmic disorganization. These changes in the internal structures of vitrified plants were reflected in their abnormal morphology and physiology.