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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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Md. Shahidul Islam, Makoto Yoshimoto, Koji Ishiguro, Shigenori Okuno and Osamu Yamakawa

The phenolic content and the radical scavenging activity were compared in leaves of sweetpotato (Ipomoea batatas L.) cultivars Shimon-1, Kyushu-119 and Elegant Summer grown under different temperature and shading conditions. Compared to cultivar differences, there was less effect of temperature and shading on the total phenolic content in sweetpotato leaves, however certain polyphenolic components differed widely among the treatments. The positive correlation between the radical scavenging activity and the level of total phenolics (r = 0.62) suggests that phenolic compounds are important antioxidant components of sweetpotato leaves. All the reverse-phase high-performance liquid chromatography (RP-HPLC) profiles of the cultivars tested showed peaks at the same retention times but peak areas of individual phenolic compounds differed with respective temperature and shading treatments. The phenolic compounds identified in the sweetpotato leaf were caffeic acid, chlorogenic acid, 4,5-di-O-caffeoylquinic acid, 3,5-di-O-caffeoylquinic acid, 3,4-di-O-caffeoylquinic acid, and 3,4,5-tri-O-caffeoylquinic acid. Most of the phenolic compounds were highest in leaves from plants grown at 20 °C without shading except 4,5-di-O-caffeoylquinic acid. The results indicate that growing leaves under moderately high temperatures and in full sun enhances the accumulation of phenolic components. These phenolic components have possible value in enhancing human health.

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C.S. Prakash, U. Varadarajan and A. S. Kumar

Development of a gene transfer system will enable rapid introduction of agronomically useful genes into elite cultivars of sweet potato. We compared microprojectile bombardment and Agrobacterium cocultivation approaches to introduce foreign genes into the genome of two sweet potato cultivars. Chimeric marker genes (gusA and kan) were successfully introduced into cvs. Jewel and TIS-70357 using both approaches. However, transgenic plants were generated in vitro using only the Agrobacterium approach. Callus and root isolates with stable expression of gusA gene were obtained using the microprojectile method. Expression of the screenable marker gusA gene was detected by histochemical assays. Integration of the introduced gene into the genome of sweet potato was confirmed by polymerase chain reaction (PCR) amplification of the kan gene and Southern blot analyses. Transgenic sweet potato plants from two cultivars are being raised and studied for quantitative expression and localization of the introduced genes. These results show that foreign genes can be successfully introduced and expressed in sweet potato. Current efforts are directed at optimizing several variables to increase the transformation efficiencies and to generate transgenic cultivars with foreign genes of agricultural importance.

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Victor A Khan, C. Stevens, T. Mafolo, C. Bonsi, J.Y. Lu, E.G. Rhoden, M. A. Wilson, M. K. Kabwe and Y. Adeyeye

TU-82-155 and `Georgia-Jet' early maturing. `Carver II'. TU-1892 and `Rojo-Blanco' late maturing sweepotato cultivars were evaluated in the field for: leaf area index (LAI), net assimilation rate, foliage crop growth rate (FCGR), storage roots crop growth rate (RCGR) and alpha a (the mean relative growth rate in dry wt to the mean relative growth rate in leaf area over a time interval) or the partitioning of assimilates. A split plot design was used and plants were sampled at 6, 8, 11 and 16 wk after transplanting. The results from study showed that LAI reached maximum development 8 and 12 wk after transplanting for early and late maturing cultivars, respectively. All cultivars irrespective to maturity groups showed a reduction in net assimilation rate 6 wk after transplanting while FCGR for early maturing cultivars gradually declined 6 wk after transplanting and varied among late maturing cultivars. `Carver II' showed increases in FCGR up to 11 wk after transplanting then rapidly declined while `Rojo-Blanco' and TU-1892 began to decline 8 and 6 wk after transplanting, respectively. RCGR showed rapid increases (100 g.m /area/week) and (150 g/m /area/week) for early and late maturing cultivars beginning 6 wk after transplanting and this increase continued until the 12th and 8 th wk after transplanting for early and late maturing cultivars, respectively. Cultivars from both maturity groups began to produce surplus assimilates (Alpha a) 6 wk after transplanting. which coincided with the rapid increases in RCGR at the same time. Thus indicating that storage root enlargement begins after the plant had accumulated a surplus of assimilates.

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Janice R. Bohac, Alfred Jones and Daniel F. Austin

Previous work in this laboratory identified high levels of unreduced (2n) pollen in the tetraploid (4×) Ipomoea spp. Acc. 81.2. This work provided indirect evidence that 2n pollen was involved in the evolution of the 6x ploidy level of the cultivated sweetpotato (I. batatas). To further study the role of 2n pollen in sweetpotato evolution, we examined plants of Acc. 81.2. plants of five sweetpotato cultivars, and 100 randomly selected heterozygous sweetpotato seedlings. The 4× Acc. 81.2 was determined to be I. batatas. High levels of large 2n pollen were confirmed in Acc. 81.2, and low levels of 2n pollen were observed in `Sulfur' and in 16% of the sweetpotato seedlings. Presence of monad, dyad, and triad sporads confirmed that the large 2n pollen grains were the result of nonreduction in the sporad stage. These new findings are direct evidence that 2n pollen was involved in the evolution of the 6× ploidy level of sweetpotato. This is the first report of a 4× accession classified as I. batatas; it is also the first report of 2n pollen in 6× I. batatas The widespread presence of 2n pollen in sweetpotato suggests that the trait can be used to advantage in breeding programs to introgress genes from wild 4× Ipomoea spp. into cultivated 6× sweetpotato without adverse effects on genetic stability or fertility.

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Vital Hagenimana, Ronald E. Simard and Louis-P. Vézina

In vitro activity measurements indicate that storage sweetpotato roots contain high amounts of extractable amylolytic enzymes. These storage roots also have a very high starch content, a characteristic indicating that the in vitro measurements estimate potential amylolytic activity rather than actual physiological activity. We are interested in optimizing the use of endogenous amylases when processing sweetpotato roots and have undertaken a study to identify physiological parameters that control in vivo starch breakdown. Sweetpotato roots were allowed to germinate for 35 days in controlled conditions. Using a combination of in vitro activity measurements and immunochemical detection, the spatial distribution and changes in activity levels for the three major amylolytic enzymes in storage sweetpotato roots—α-amylase, β-amylase, and starch phosphorylase—have been followed. After 6 days, α-amylase protein increased in the outer starchy parenchymatous tissues surrounding the cambium layers, a result suggesting a de novo synthesis of the enzyme in cambium or laticifers layers. β-Amylase was abundant throughout the root at all times, and its high levels did not directly affect starch degradation rates. Starch phosphorylase protein level remained constant, while its extractable activity increased. Starch content decreased during sweetpotato seed root germination. However, the amount of starch that disappeared during germination was low compared with the calculated starch hydrolysis potential estimated by amylolytic activity measurements.

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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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Benard Yada, Phinehas Tukamuhabwa, Bramwell Wanjala, Dong-Jin Kim, Robert A. Skilton, Agnes Alajo and Robert O.M. Mwanga

. Delacy, I.H. 1994 Interpretation of random amplified polymorphic DNA marker data for fingerprinting sweetpotato [ Ipomoea batatas (L.) Lam] genotypes Theor. Appl. Genet. 88 332 336 Diaz, J. Schmiediche, P

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William B. Thompson, Jonathan R. Schultheis, Sushila Chaudhari, David W. Monks, Katherine M. Jennings and Garry L. Grabow

adventitious roots in sweetpotato ( Ipomoea batatas ) Austral. J. Bot. 52 551 558 Beyene, K. Nebiyu, A. Getachew, M. 2015 Effect of number of nodes and storage duration of vine cuttings on growth, yield and yield components of sweet potato ( Ipomoea batatas L

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Arthur Villordon, Wambui Njuguna, Simon Gichuki, Philip Ndolo and Don Labonte

:// >. Gichuki, S.T. Berenyi, M. Zhang, D. Hermann, M. Schmidt, J. Glössl, J. Burg, K. 2003 Genetic diversity in sweetpotato [ Ipomoea batatas (L.) Lam.] in relationship to geographic sources as assessed with RAPD markers Genet. Resources Crop Evol. 50 429 437