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Etienne L. LeRiche, Gefu Wang-Pruski, and Valtcho D. Zheljazkov

After-cooking darkening (ACD) is an undesirable potato tuber trait, problematic in processed potato products ( Wang-Pruski and Nowak, 2004 ). It is characterized as a change from a tuber's normal flesh color to gray, blue, purple, or black

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Chen-Yi Hung, John R. Murray, Sarah M. Ohmann, and Cindy B.S. Tong

The color of red potato tubers is due to an accumulation of anthocyanins in periderm and peripheral cortex tissues. The objective of this study was to characterize changes in anthocyanin content and tuber surface color during tuber development. Using the red tuber-producing potato (Solanum tuberosum L.) cultivar Norland, we observed that chroma (intensity of redness) and anthocyanin content per unit of surface area of greenhouse-grown tubers decreased as tuber weight increased. There was no increase in hue (tint) during the same developmental periods. Using high-performance liquid chromatography (HPLC), we determined that pelargonidin and peonidin are the major anthocyanidins (aglycones of anthocyanins) in the tuber periderm. Northern blot analyses indicated that steady-state mRNA levels of dihydroflavonol reductase (DFR), an anthocyanin biosynthetic enzyme, continued throughout tuber development. These results suggest that anthocyanins are synthesized throughout tuber development, and that cell division and/or enlargement contribute to a decline in chroma and anthocyanin concentration.

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Félix H. França and Ward M. Tingey

for the fellowship that supported this work. This research was also supported in part by the International Potato Center, grants from USDA-CSRS, and Hatch project NYC 139416. The cost of publishing this paper was defrayed in part by the payment of page

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Kimberly J. Felcher, D.S. Douches, W.W. Kirk, R. Hammerschmidt, and W. Li

Research was done to determine if enhanced resistance to potato (Solanum tuberosum L.) late blight could be obtained by combining host plant resistance and engineered resistance. Late blight susceptible cultivars, Atlantic, and Spunta and the partially resistant cultivar Libertas were transformed with a fungal glucose oxidase gene, resulting in lines which ranged in transgene copy number from 1 to 8. Glucose oxidase enzyme activity ranged from 0.00 to 96.74×10-5 units/mg plant tissue. There was no correlation between copy number and level of transgene mRNA, level of transgene mRNA and enzyme activity, or between level of enzyme activity and disease resistance. Field and growth chamber evaluation of late blight response demonstrated little to no effect of the glucose oxidase transgene in either late blight susceptible or partially late blight resistant cultivars. However, enzyme activity levels were much lower than levels reported in previous research, which may account for the lack of effect of glucose oxidase against Phytophthora infestans. Twenty-one percent of the transgenic lines were phenotypically off-type compared to nontransgenic controls. Most of the off-type transgenic lines (four out of seven) were derived from `Libertas'. Because several off-type lines did not express the glucose oxidase protein, this phenomenon could not be attributed solely to the glucose oxidase transgene. Based on these results, transgenic lines produced for this study do not increase resistance to P. infestans even in combination with moderate host plant resistance. However, production of greater numbers of transgenic lines with the current construct or, production of transgenic lines in which a different constitutive promoter drives the expression of the glucose oxidase gene might result in greater disease resistance. However, the usefulness of any small increase in resistance would need to be evaluated against the time and cost required for development of transgenic potato cultivars and the potential for off-type tubers and plants.

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Qin Chen and Hai Y. Li

1 To whom reprint requests should be addressed; e-mail chenqi@agr.gc.ca . The authors thank Dermot Lynch and Debbie Beasley for providing the two cultivated potato lines and for the propagation of the potato

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Christian T. Christensen, Lincoln Zotarelli, Kathleen G. Haynes, and Charles Ethan Kelly

S olanum chacoense (2 n = 2 x = 24) is a wild potato species that is native to South America. It has been evaluated for several traits of interest for future incorporation in commercially produced potato, such as greater root biomass linked to

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Charles R. Brown

There are many different plant species where Luther Burbank was responsible for innovative creations. Potato is one of these. Luther Burbank’s potato breeding must be seen from an historical perspective. Potatoes were found in South America by

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Robert P. Sabba and Bill B. Dean

Hort/LA Paper No. 92-14. Project No. 4002. College of Agriculture and Home Economics Research Center, Washington State University, Pullman, WA 99164. This work was supported by the National Potato Council (U.S. Dept. of Agriculture), Grant No. 58

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Joseph J. Coombs, David S. Douches, Susannah G. Cooper, Edward J. Grafius, Walter L. Pett, and Dale D. Moyer

This publication was made possible through support provided by the Michigan Agriculture Experiment Station, USDA/ARS cooperative agreement 59-0790-2-060, and the Michigan Potato Industry Commission.

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Joseph J. Coombs, David S Douches, Wenbin Li, Edward J. Grafius, and Walter L. Pett

This publication was made possible through support provided by the Michigan Agriculture Experiment Station and the National Potato Council. The research was also supported by the Office of USAID/CAIRO/AGR/A, under cooperative Agreement No. 263