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James M. Crosslin

United States, the primary vector of TRV is P. allius ( Mojtahedi et al., 2000 ). When the virus is transmitted to developing potato ( Solanum tuberosum ) tubers, internal symptoms are produced consisting of rings, arcs, and various dark blotches that

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Roger L. Vallejo, Wanda W. Collins, and Robert H. Moll

submitted from a dissertation by R.L. Vallejo in partial fulfillment of the requirements for a Ph.D and was entirely supported by the International Potato Center, Lima, Peru. We gratefully acknowledge the technical assistance of Suzanne Belding and Rocco

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Noël Pallais

True potato seed of Atzimba × 104.12LB (intermediate dormancy) was dried to seed moisture contents ranging from 3.85 to 12.5% (dry wt basis) and was stored for 2 years at 30, 15 and 5°C. Seed was tested for various germination and seedling vigor criteria at 4 month intervals. Seed dormancy and viability were better preserved at seed moisture levels below 7% and as temperature decreased. High moisture (>9%) was lethal to seed stored at 30°C. TPS should be stored at <5% seed moisture content. Under this condition seed dormancy in the genotype studied was lost after about 12 months at 30°C.

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B. Sosinski and D.S. Douches

Potato Industry Commission and Michigan Agricultural Expt. Station. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to

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Sandra E. Vega, Jiwan P. Palta, and John B. Bamberg

1 Research assistant. 2 Campbell-Bascom professor of horticulture; to whom reprint requests should be addressed. 3 Geneticist. The authors thank the Inter-Regional Potato Introduction Station for providing seeds, and colleagues at the Stress

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J. Gill, C. Laguë, N. Lehoux, and R-M. Duchesne

We investigated the use of propane flamers in potato production. The thermal sensitivity of young potato plants and Colorado potato beetles (CPB) (eggs, larvae, adults) were determined in the laboratory and then validated in the field. The thermal treatment intensities for top killing prior to harvest were also determined both in the laboratory and in the field for three potato varieties and compared to chemical defoliant. The results obtained showed that young potato plants (0 to 10 cm) can recover from flaming treatments targeted against weeds and CPB early into the growing season. Effective thermal top killing is dependent upon potato variety (foliage density) and maturity level and inducement of sufficient temperature rise within the potato plant canopy to effectively control fall populations of CPB. A thermal strategy for weed and CPB control and top killing was elaborated and compared to chemical pesticides in term of operating costs.

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T.W. Tibbitts, J.G. Croxdale, C.S. Brown, and R.M. Wheeler

Leaf cuttings from 6-week-old potato plants were planted into the Astroculture flight unit for the STS-73 shuttle flight in Oct. 1995. Tubers developed in the axils of the five leaf cuttings during the 16-days in microgravity. The flight unit had a closed growth chamber maintained at 22°C, 82% relative humidity, 150 μmol·m–2·s–1 photosynthetic photon flux, and with carbon dioxide controlled during the light period to ≈400 μmol·mol–1 and exceeding 4000 μmol·mol–1 during the dark period. A controlled delivery system using a porous tube system in arcillite medium provided water to the cuttings. A camera mounted in the top of the chamber provided video images of the plants at 2-day intervals. The cuttings maintained good vitality for the first 12 days of the flight followed by senescence of the leaves. Tubers 1.5 cm in diameter and weighing 1.7 g were produced. The shape and size of the tubers, the internal cell arrangement, and the size range of the starch grains, were similar on cuttings developed in a control experiment on the ground. Also the concentrations of starch, sucrose, fructose, glucose, and total soluble protein in the cuttings from space were similar to the cuttings developed on the ground. The challenges in scheduling experiments in a space flight and in conducting comparison control experiments on the ground are discussed. Environment control variations associated with cabin pressure changes, venting requirements, and air sampling are reviewed.

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Richard O. Nyankanga, Ocen Modesto Olanya, Hans C. Wien, Ramzy El-Bedewy, John Karinga, and Peter S. Ojiambo

Late blight, caused by Phytophthora infestans (Mont.) de Bary, accounts for significant losses in potato production worldwide ( Erwin and Ribeiro, 1996 ). The pathogen infects foliage and tubers resulting in tuber yield loss attributable to

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Jean-Pierre Goffart, Marguerite Olivier, and Marc Frankinet

Improving NUE is important for potato crops because of their relatively poor ability to take up available soil N. Either excess N or N deficiency can have detrimental effects on yield, tuber quality, and the environment. However, potato producers in

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Janet E.A. Seabrook and Gerald Farrell

Stock plants of `Shepody' and `Yukon Gold' potato (Solarium tuberosum L.) were grown in a greenhouse and irrigated with city water. Contamination rate of stem explant tissue cultures excised from these stock plants was 50% to 100%. A comparison of the microorganisms isolated from the contaminated cultures and from 0.22-μm filter disks through which 20 liters of city water had passed revealed the presence of similar bacterial floras. Five genera of bacteria (Listerium spp., Corynebacterium spp., Enterobacter spp., Pasteurella spp., and Actinobacillus spp.) were isolated from contaminated cultures and cultured filter disks. Watering greenhouse-grown stock plants with filtered city water decreased contamination of stem explant cultures 30% to 50%. Installing an ultraviolet light water-sterilizing unit at the greenhouse inlet point effectively reduced contamination.