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Joan R. Davenport and Mary J. Hattendorf

Potatoes (Solanum tuberosum L.) are grown extensively throughout the Pacific northwestern United States as a high value crop in irrigated rotations with other row crops such as wheat (Triticum aestivum L.) and both field and sweet corn (Zea mays L.). Center pivots are the predominant irrigation systems. Soil texture ranges from coarse sands to finer textured silt loams and silts and can vary within one field, particularly in fields with hilly topography. Site specific management is being evaluated as an approach to help to optimize inputs (water, seed, agricultural chemicals) to maintain or enhance yield and reduce potential negative environmental impacts from these farming systems. Currently, variable rate fertilizer application technology and harvest yield monitoring equipment are commercially available for potato. Variable rate seeding and variable rate irrigation water application technologies are developed but not fully commercialized and variable rate pesticide application equipment is in development. At the Irrigated Agricultural Research and Extension Center in Prosser, Wash., we have a team of research scientists, interested individuals from local industry, and other key organizations (e.g. local conservation districts) who are working together to evaluate different site specific technologies, improve the ability to use available tools, and to improve decision-making ability by conducting research both on farm and in research plots.

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Dominique Michaud, Serge Overney, Binh Nguyen-Quoc, and Serge Yelle

In the past few years, transformation of plant genomes with proteinase inhibitor (PI) genes has been proposed as an effective way to produce insect-tolerant plants. For such a control approach, however, biochemical studies are necessary to assess the effect of PIs on not only insect digestive proteinases (target enzymes) but also plant endogenous proteinases (nontarget enzymes). As an example, transformation of potato (Solanum tuberosum L.) with oryzacystatin (OC) genes, two cysteine PIs, was considered for controlling Colorado potato beetle (CPB; Leptinotarsa decemlineata Say). The use of electrophoretic approaches and standard assays showed that CPB uses at least 14 cysteine proteinases for protein digestion throughout its development. Proteinases of the same class were also detected in sprouting potato tuber extracts, suggesting a potential interference of cPIs in transgenic plants. While OCs inhibit a significant fraction of CPB digestive proteinases, no inactivation of potato proteinases was detected. This apparent absence of direct interference suggests the real potential of OCs for producing CPB-tolerant transgenic potato plants.

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B.Z. Escalante and Alan R. Langille

Disinfested, etiolated medial segments of potato (Solanum tuberosum L.) sprouts cv. Katahdin with two axillary buds were placed on Murashige and Skoog (MS) medium in clear plastic culture boxes. Basal ends of explants were inserted into MS medium containing BA at 2 mg·liter–1. Nine treatments, composed of factorial combinations of GA3 at 0, 0.2, and 2 mg·liter–1 and IAA at 0, 0.3, and 3 mg·liter–1, were imposed. These were applied via small agar cylinders placed on the apical cut surface of each segment. Regardless of the presence of cytokinin and auxin, no rhizomes developed after 3 weeks in culture without a supply of GA3. Number and length of primary and secondary rhizomes increased with an increase in GA3 concentration in the agar cylinder from 0 to 2 mg·liter–1. Rhizome initiation and development appear to be controlled by coordinated participation of endogenous plant hormones during the early events leading to tuber development. Chemical names used: 2,4a,7-trihydroxy-1-methyl-8-methylenegibb-3-ene-1,10-carboxylic acid 1->4 lactone (GA3); indole-3-acetic acid (IAA); N-(phenylmethyl)-1H-purin-6-amine (BA).

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Weixing Cao and Theodore W. Tibbitts

Plants of the potato (Solanum tuberosum L.) cultivars Denali, Norland, Haig, and Kennebec were grown for 42 days under three temperature cycling periods (thermoperiods) with continuous irradiation in two repeated experiments to help determine if temperature cycling might be varied to optimize tuber development of potatoes in controlled environments. Thermoperiods of 6/6 hours, 12/12 hours and 24/24 hours were established with the same temperature change of 22/14C and same controlled vapor pressure deficit of 0.60 kPa. The thermoperiod of 24/24 hours significantly promoted tuber initiation but slowed tuber enlargement in all four cultivars, compared to the thermoperiods of 6/6 hours and 12/12 hours. `Denali' produced the highest tuber and total dry weights under the 6/6 hours thermoperiod. `Kennebec' produced the highest tuber dry weight under the 12/12 hours thermoperiod. Thermoperiods had no significant effect on shoot and root dry weights of any cultivars. The major effect of thermoperiod was on initiation and enlargement of tubers.

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Juan M. Ruiz, Joaquín Hernández, Nicolas Castilla, and Luis Romero

Potato (Solanum tuberosum L.) `Spunta' plants were grown with the root zone covered by different types of polyethylene plastic mulches. The plastic mulches used were transparent, white, co-extruded black and white, and black. As a control, plants were grown without plastic mulch. The parameters analyzed were soil temperature, root concentration of K and Ca, and enzymatic activities of ATPase and pyruvate kinase (PK), measured as basal and in the presence of K+ and Ca2+. The physical characteristics of the plastic mulches directly influenced soil and root temperatures in potato plants. In addition, the concentration of cations in the roots (particularly Ca2+) and basal ATPase activity were affected by soil temperature, whereas basal PK was not affected by soil temperature. The use of co-extruded black and white plastic mulch improved the nutritional status of Ca in the roots of potato plants. Finally, the basal ATPase and PK activities in the presence of K+ and Ca2+ were related with the root levels of these cations.

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Junne-Jih Chen and Yu-Ju Liao

The effect of N source on `Kennebec' potato (Solanum tuberosum L.) tuberization was investigated using single-node segments originated from in vitro virus-free plantlets and inoculated on media with two nitrate: ammonia ratios (low, 2:1; high, 5:1). Cell count and size and sugar-use characteristics were measured at intervals of tuber development. Tubers grown on high nitrate-ammonia medium exhibited higher rates of sucrose use and higher dry-matter accumulation than tubers grown on low nitrate-ammonia medium. The median value of tuber fresh weight increased from 0.66 to 1.23 g as a result of increasing nitrate-ammonia. Significant differences in cell size and growth rate were observed between the two N treatments. There was also a high correlation between tuber cell size and dry matter (r = 0.82, P ≤ 0.05). These data demonstrate the importance of the nitrate: ammonium ratio in determining C use, tuber cell size, and tuber weight. Chemical names used: α-naphtylacetic acid (NAA); 6-benzylaminopurine (BA).

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Jin-Cheol Jeong, Robert K. Prange, and Barbara J. Daniels-Lake

Potato (Solanum tuberosum L. `Russet Burbank' and `Shepody') tubers were exposed to continuous 4 μL·L-1 (166 μmol·m-3) ethylene in air. Treatment started after 8 weeks in storage and continued up to 33 weeks of storage at 9 °C over one (`Russet Burbank') or two (`Shepody') storage seasons. Tubers were sampled at 3 week (`Shepody') or 5 week (`Russet Burbank') intervals for polyamine content [putrescine, (PUT); spermidine, (SPD); and spermine, (SPM)] and sprout number and fresh weight per tuber. During the storage period, `Shepody' had higher concentrations of all three polyamines and a higher PUT/(SPD + SPM) ratio, compared with `Russet Burbank'. All three polyamines in both cultivars increased during storage, and the increase was more rapid in `Shepody' than in `Russet Burbank'. Regardless of cultivar and year, exposure to ethylene induced higher spermidine (SPD) content and a lower PUT/(SPD + SPM) ratio, compared with the air treatment. Sprouts appeared later and were smaller on ethylene-treated tubers and were more numerous in `Russet Burbank'. These long-term ethylene effects may be due, in part, to enhanced transformation of PUT to SPD.

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Kathleen G. Haynes, William E. Potts, Jesse L. Chittams, and Diane L. Fleck

For the yellow-flesh fresh market, potato (Solanum tuberosum L.) varieties with intense yellow flesh are desired. Twenty-five yellow-flesh clones, including 24 U.S. Dept. of Agriculture (USDA) selections and the check variety `Yukon Gold', were evaluated for tuber yellow-flesh color, as measured by a reflectance colorimeter, and for individual tuber weight in replicated field trials in Presque Isle, Maine, in 1991 and 1992. There were significant differences among clones for yellow-flesh intensity. Yellow-flesh intensity in two USDA selections was significantly less than in `Yukon Gold'. In four USDA selections, yellow-flesh intensity was significantly greater than in `Yukon Gold'. In general, there was an inverse relationship between tuber weight and yellow-flesh intensity. Subsamples of tubers whose weight fell between the 10 to 90, 25 to 75, 35 to 65, and 40 to 60 percentile were compared to the full sample. There was good agreement between the 10 to 90 and 25 to 75 percentile subsample and the full sample regarding the average yellow-flesh intensity and in the consistency of pairwise comparisons between individual selections and `Yukon Gold'. For determining yellow-flesh intensity, the 25 to 75 percentile subsample was as informative as the full sample.

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Joan R. Davenport

Potato (Solanum tuberosum L.) is grown extensively throughout the Pacific Northwest as a high-value crop in irrigated rotations with other row crops such as wheat (Triticum aestivum L.) and corn (Zea mays L.)—both field and sweet. Center pivots are predominant irrigation systems. Soil texture ranges from coarse sands to finer textured silt loams and silts and can vary within one field, often with very hilly topography. Site-specific management is being evaluated as an approach to help to optimize inputs (water, seed, agricultural chemicals) to maintain or enhance yield and reduce the potential of negative environmental impacts in these farming systems. Currently variable rate fertilizer application technology and harvest yield monitoring equipment are commercially available for these systems. Variable rate seeding and variable rate irrigation water application technologies are developed but not fully commercialized and variable rate pesticide application equipment is in development. At the Irrigated Agr. Res. and Ext. Ctr. in Prosser, Wash., we have a team of research scientists (both university and USDA/ARS), interested individuals from local industry, and other key organizations (e.g., local conservation districts) who are working together to evaluate different site specific technologies, improve the ability to use available tools, and to improve decision-making ability by conducting research both on farm and in research plots.

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Meghan A. Curless and Keith A. Kelling

Within Wisconsin, there is a distinct movement toward dairy herd expansion and consolidation of small farms. These large dairies are considering various land and manure management arrangements with non-livestock farmers, such as potato (Solanum tuberosum) producers to increase their manure management options. This study used a fertilizer equivalence approach to evaluate the availability of nitrogen from dairy manure to potatoes. Nitrogen (N) availability was evaluated in field experiments in 2000 and 2001, conducted in northeast Wisconsin using a moderate and a high liquid dairy manure rate [10,000 and 20,000 gal/acre (93,536 and 187,072 L·ha-1)] compared with results obtained from N fertilizer applied at five rates [0 to 240 lb/acre (269.0 kg·ha-1)]. Availability estimates using the fertilizer equivalence method based on tuber yield, harvested tuber N concentration and uptake, petiole nitrate concentration, and soil nitrate levels resulted in apparent availability of manurial N from 10% to 40%, with an overall average across both years of 29.2%. This level is only slightly less than values typically measured where corn has been used as the test crop. In spite of being more shallow-rooted and perhaps somewhat less efficient in N use it does not appear that adjustments to manurial N availability estimates are warranted when potatoes are grown.