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

The Colorado potato beetle [Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae)] is a destructive pest of the cultivated potato (Solanum tuberosum L.) in northern latitudes. Combining resistance mechanisms of leptine glycoalkaloids and glandular trichomes with the synthetic Bacillus thuringiensis Berliner (Bt) cry3A gene in potato may be an effective strategy for controlling the Colorado potato beetle. Bt-cry3A transgenic plants were developed for three potato lines with differing levels of resistance to Colorado potato beetle ['Yukon Gold' (susceptible control), USDA8380-1 (leptine glycoalkaloids), and NYL235-4 (glandular trichomes)]. Polymerase chain reaction, and Southern and northern blot analyses confirmed integration and transcription of the cry3A gene in the transgenic lines. Detached-leaf bioassays of the cry3A engineered transgenic lines demonstrated that resistance effectively controlled feeding by first instar Colorado potato beetles. The susceptible `Yukon Gold' control suffered 32.3% defoliation, the nontransformed high foliar leptine line (USDA8380-1) had 3.0% defoliation, and the nontransformed glandular trichome line (NYL235-4) had 32.9% defoliation. Mean percentage defoliation for all transgenic lines ranged between 0.1% and 1.9%. Mean mortality ranged from 0.0% to 98.9% among the Bt-cry3A transgenic lines, compared to 20% for the susceptible `Yukon Gold' control, 32.2% for USDA8380-1, and 16.4% for NYL235-4. Results indicate that genetic engineering and the availability of natural resistance mechanisms of potato provide the ability to readily combine host plant resistance factors with different mechanisms in potato.

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Hyo-Won Seo, Jung-Yoon Yi, Young-Il Hahm, Hyun-Mook Cho, and Kuen Woo Park

Three potato (Solanum tuberosum L.) cultivars `Superior', `Irish Cobbler', and `Jopung' were transformed by co-cultivation with tuber discs and disarmed Agrobacterium tumefaciens LBA4404 carrying modified vector pBI121, that contained PLRV coat protein (CP) gene and controlled by CaMV35S promoter. Putative transformants were selected and their genomic DNA and RNA transcripts were analyzed for the confirmation of genetic stability by RT-PCR, PCR, southern, and northern blot. The growth characteristics and viral resistance of progenies of transgenic potato plants were investigated. Twelve lines among the different seven-times manipulated transgenic lines were grown in greenhouse and isolates trial field. PLRV coat protein gene was stably inherited in `Superior', but not in `Jopung'. `Jopung' was less stable than `Irish Cobbler' and `Superior' at genetic stability of PLRV CP gene. And some of these transgenic lines were highly resisted in PLRV multiplication. The yield of transformants was reduced in `Irish Cobbler' but not in `Superior'. Possible explanations for these types of resistance are gene silencing and positional effects of transformed PLRV CP genes and that had cultivar specificity. We consider the appearance of escaped transformants in `Jopung' for emergence of chimeric explants from early selection stage.

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Anusuya Rangarajan, A. Raymond Miller, and Richard Veilleux

Leptine (LP) glycoalkaloids have been demonstrated to confer natural resistance to the Colorado potato beetle (CPB) in Solanum chacoense (chc). Development of cultivated potatoes with natural resistance to CPB has the potential to reduce both costs and environmental impacts of production by reducing pesticide use. To introgress the genes conferring leptine production from chc into S. tuberosum (tbr), clones of chc have been crossed with clones of S. phureja. Leaf disks from eight hybrids were subjected to a CPB second instar feeding bioassay to determine if extent of feeding was related to LP levels. Most hybrids contained leptinidine (LD, the aglycone of LP) levels intermediate to chc and tbr, and insect feeding was suppressed 30% to 50% in hybrids containing >10 mg·g–1 DW LD. One hybrid displaying feeding suppression contained a very low level of LD, whereas another hybrid that contained higher levels of LD had higher feeding rates. The presence of LD at “threshold” levels in these hybrids will suppress feeding of CPB, but other factors affecting resistance are also present and need to be explored.

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J.R. Davenport, R.G. Stevens, E.M. Perry, and N.S. Lang

The ability to monitor plant nutrient status of high value horticultural crops and to adjust seasonal nutrient supply via fertilizer application has economic and environmental benefits. Recent technological advances may enable growers and field consultants to conduct this type of monitoring nondestructively in the future. Using the perennial crop apple (Malus domestica) and the annual crop potato (Solanum tuberosum), a hand-held leaf reflectance meter was used to evaluate leaf nitrogen (N) status throughout the growing season. In potato, this meter showed good correlation with leaf blade N content. Both time of day and time of season influenced leaf meter measurement, but leaf position did not. In apple, three different leaf meters were compared: the leaf spectral reflectance meter and two leaf greenness meters. Correlation with both N rate and leaf N content were strongest for the leaf reflectance meter early in the season but nonsignificant late in the season, whereas the leaf greenness meters gave weak but significant correlations throughout the growing season. The tapering off of leaf reflectance values found with the hand-held meter is consistent with normalized difference vegetation index (NDVI) values calculated from satellite images from the same plots. Overall, the use of leaf spectral reflectance shows promise as a tool for nondestructive monitoring of plant leaf status and would enable multiple georeferenced measurements throughout a field for differential N management.

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Erik J. Sorensen and Loretta J. Mikitzel

Specialty potatoes have been evaluated in a number of on-farm trials conducted by Washington State Univ. Cooperative Extension. This work has led to the commercial success of a number of yellow- and purple-fleshed potato cultivars in Washington. These cultivars are currently marketed as fresh potatoes for baking and boiling. In 1992, the processing quality of selected specialty potato cultivars was evaluated. Twenty-five cultivars were prepared as chips and french fries and evaluated for taste, color, and market acceptance. Evaluators noticed differences in flavor and texture, as well as in color, and the scores of individual cultivars varied widely. Strong opinions were expressed on the market acceptance of the various yellow-, orange-, pink-, and purple-fleshed cultivars. A majority of evaluators said that they would buy chips and french fries made from specialty potatoes.

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Kathleen B. Evensen, Joseph M. Russo, and Harriet Braun

Grading criteria are proposed for judging potatoes (Solanum tuberosum) for chip quality and yield. The criteria were derived from a decision-making scheme developed from expert opinions, U.S. Dept. of Agriculture grades, and a statistical evaluation of stored potatoes. The criteria are presented as ranges of acceptable values for a limited set of variables found to be important for chip quality and yield. These variables include bruising, cracks, cuts, fusarium dry rot, lesions, and scab. The proposed criteria, besides being a practical decision-making tool for processors, could serve as a knowledge base for potato expert systems and the development of mechanized sorting equipment.

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Mack A. Wilson and Victor A. Kahn

Four row covers (clear and white slitted), spunbonded polyester, and VisPore were used on `Atlantic' potato cultivar at Charleston, Missouri. Row covers were installed on March 6, 1991 and removed on May 5, 1991. No significant differences were observed with orthoganal comparisons on grade A, B, and total number of potatoes among row covers. Total yields were higher with row covers and the data was significant. Potato plant heights were greater with row covers and the data was significantly different when the control was compared with row covers.

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Wayne C. Porter

Selected herbicides, alone or in combination with polyethylene bed covers, were evaluated for preemergence weed control in sweet potato plant beds. No injury to sweet potato transplants was found when the herbicide was applied to the soil surface of freshly bedded sweet potato roots before application of the polyethylene or was applied to newly emerged transplants immediately after the bed cover was removed. Some foliar chlorosis was observed in transplants from beds treated with clomazone, but after the first transplant pulling, no reappearance occurred. Clomazone, chloramben, and napropamide provided excellent control of all annual grasses. Herbicides, regardless of timing of application, did not adversely affect number or weight of sweet potato transplants. Beds covered with polyethylene film produced more transplants at the early and total harvests than the uncovered beds.

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C.R. Brown, C.G. Edwards, C.-P. Yang, and B.B. Dean

Potatoes with orange flesh were found in cultivated diploid (2n = 24) potato populations derived from Solanum stenotomum Juz. et Buk. and S.phureja Juz. et Buk. The orange flesh trait was found to be controlled by an allele at the Y- locus designated Or. Or is dominant over Y and y, which control yellow and white flesh, respectively. In a comparison of white and orange flesh segregants from crosses, the orange was associated with large amounts of zeaxanthin, a xanthophyll previously not reported as a constituent of potato flesh carotenoids. The combined total of lutein and zeaxanthin was four times higher than the highest carotenoid composition previously reported for potato, this is about one-sixth the total carotenoid content of carrot with standard carotenoid levels, although lutein and zeaxanthin do not possess provitamin A activity.

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W.R. Stevenson, D. Curwen, K.A. Kelling, J.A. Wyman, L.K. Binning, and T.R. Connell

The Wisconsin potato crop is managed intensively through multiple inputs of pesticide, fertilizer, and irrigation. Beginning in 1979, a multidisciplinary team at the Univ. of Wisconsin developed an effective Integrated Pest Management Program to address key management decisions associated with this crop. The program fostered the development of several private IPM businesses and continues to help increase the acceptance of IPM technology by the potato industry. Results of component and integrative research, funded by industry, state, and federal sources, provided the essential ingredients for development of computer software now used for managing the potato crop on ≈ 70,000 acres (28,330 ha) of potatoes in a multistate area. The software helps growers determine the need for and timing of critical crop inputs. By reducing or eliminating unneeded pesticide and irrigation applications, the software helps to improve overall production efficiency. Industry adoption of this software is providing the impetus for development of more comprehensive software that includes additional aspects of potato production as well as the production of crops grown in rotation with potato.