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G.W. Stutte, C.L. Mackowiak, N.C. Yorio, R.M. Wheeler, and L.M. Ruffe

An experiment was conducted in the Biomass Production Chamber (BPC) at Kennedy Space Center to determine the feasibility of continuous steady-state production of potato (Solanum tuberosum L.). Plants were grown in a “batch” or continuous production mode using either 0.5 × modified Hoaglands or effluent from aerobically processed inedible potato biomass as a nutrient source. EC and pH were controlled to 0.12 S·m–1 and 5.8, respectively. The batch harvest occurred after 104 days and continuous harvest occurred every 26 days, with replanting occurring in the same solution. Continuous production on “aged” solution resulted in earlier tuber initiation, reduced plant height, and smaller canopies than the “batch” treatment. Planting density of the continuous treatment was increased from eight to 16 plants/m2. Because one quarter of the planting area was harvested and replanted every 26 days, a steady-state of canopy coverage between 60% to 75% of the chamber was maintained. Steady-state of CO2 fixation was also maintained in the continuous treatment. There was no effect on either quantum efficiency, tuber yield, or harvest index of the plants grown in continuous production. Although replanting into “aged” nutrient solution resulted in earlier tuber initiation and reduced plant size, the system reached a steady state of production, which is desirable for advanced life support system.

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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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Randy J. Lewis and Stephen L. Love

Petiole NO3-N concentrations (PNCs) of seven potato (Solanum tuberosum L.) genotypes grown under four N treatments were studied. In 1986-88, the cultigens were planted in plots with a gradient of available N created by adding 0,140,280, or 420 kg N/ha ammonium nitrate split between preplant and periodic seasonal applications. PNCs were significantly (P ≤ 0.05) affected by year, sampling time (four times per season), N rate, and cultigen. All first- and second-order interactions were also significant (P <0.05). The relative PNC ranking among cultigens remained nearly constant across years when averaged across sampling dates and N rates. Regression-equation distinctiveness for each cultigen relating PNC to sampling time demonstrated a genotypic influence on seasonal PNC and allowed separation into four response classes. Using a data subset consisting of the 1988 trial, an optimal N rate was determined and regression equations were computed relating PNC to sampling date for each cultigen at the applied N rate nearest to the optimum. Tests for distinction separated the equations of the seven cultigens into six unique classes; `Frontier Russet' and `Ranger Russet' equations were coincident.

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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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K. E. Cushman and T. W. Tibbitts

Chlorosis and necrotic spotting develop on expanding leaves of particular cultivars of potato (Solanum tuberosum L.) when grown under constant light and temperature conditions. Plantlets of a constant-light sensitive cultivar, Kennebec, were planted into peat:vermiculite and established at 18C for 10 d under a 12 h light: 12 h dark photoperiod. Plants were then exposed to constant light and sprayed with 1 ml of either 0.5 mM silver thiosulfate (STS), an ethylene-action inhibitor, or water (as a control) every 2 days. Specific `target' leaflets, 5-10 mm in length at the beginning of the constant-light period, were harvested on days 5-9 of constant light, during injury development, and placed in bags made of Teflon film for IO-15 minutes to collect ethylene. Ethylene release and necrotic spotting increased as days of constant light increased for both water and STS-treated leaves, though STS-treated leaves produced slightly less ethylene and significantly less necrotic spotting than water-treated leaves. Ethylene release was correlated with extent of necrotic spotting. STS-treated plants exhibited greater dry weight and leaf area then water-treated plants. The results indicate that ethylene is not only produced by injured leaf tissue but, in addition, that ethylene may have a role in the development of constant-light injury symptoms.

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G.W. Stutte, N.C. Yorio, and R.M. Wheeler

Photoperiod treatments were imposed on potato (Solanum tuberosum L. cv. Norland) grown in the Biomass Production Chamber (BPC) at Kennedy Space Center under HPS lamps (670 μmol m-2s-1 PPF) at 1200 μmol mol-1 CO2. Stand A decreased with dark cycle length, which correlated with the change in leaf starch concentration during the dark cycle, but not absolute starch concentration. A series of growth chamber experiments were performed to characterize the effect of photoperiod and PPF on CO2 assimilation and starch mobilization in single leaves. Plants grown on a 12/12 photoperiod at either low (300 μmol m-2s-1) or high (600 μmol m-2s-1) PPF were subjected to short-term photoperiod treatments of 8/16, 16/8, and 24/0 and diurnal CO2 assimilation rates, CO2 response curves, and leaf starch content were determined. CO2 compensation point was not affected by either photoperiod or PPF. However, Amax (when normalized for PPF) decreased with increasing photoperiod. Anet correlated with the changes in specific leaf weight and starch content during the dark cycle.

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Francis Zvomuya and Carl J. Rosen

Field studies were conducted on a Hubbard loamy sand (sandy, mixed, frigid Entic Hapludoll) during 1996 and 1997 at Becker, Minn., to evaluate the effect of a polyolefin-coated urea (POCU) fertilizer (Meister, Chisso Co., Japan) on yield and quality of irrigated `Russet Burbank' potatoes (Solanum tuberosum L.). The POCU was a 3:1 mixture of 70-day and 50-day release formulations, respectively, based on historical soil temperatures at the site. The study compared five banded nitrogen (N) rates (110, 155, 200, 245, and 290 kg·ha-1 N) as a split application of urea applied at emergence and hilling, vs. POCU applied at planting. All plants received an additional 30 kg·ha-1 N as monoammonium phosphate band-applied at planting. Yields were higher in 1996 because of cooler temperatures and poor tuber set in 1997. Total and marketable yields averaged, respectively, 3.9 and 3.3 Mg·ha-1 higher with POCU than with urea. Total yield was not affected by rate of N application regardless of source, but marketable yield increased linearly with N rate. The yield of marketable tubers larger than 170 g increased linearly with N rate in both years. Gross return was 10% higher with POCU than with urea, but estimated net return showed a significant sourc × N rate interaction. The net return increased by $3.13 per kg of urea-N applied, but there was no significant change across POCU application rates.

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Y. Zhang, J.E. Abdulnour, D.J. Donnelly, and N.N. Barthakur

Micropropagation and minituber production technology may enable the establishment of potato (Solanum tuberosum L.) seed tuber certification programs in arid and semiarid regions of the world and reduce dependency on expensive seed tuber imports. Therefore, we investigated possible carry-over effects of moderate salt stress on the following production cycle. The yields of seed tuber- and microtuber-derived plants of potato, cv. Norland, grown in both nonsaline and saline (NaCl) growing conditions (pretreatment), were evaluated under nonsaline or saline irrigation (0 or 60 mm NaCl) in a greenhouse trial. Pretreatment had no effect on yield; there was no apparent residual carry-over effect of salt stress of parent plants on tuber yield of seed tuber- or microtuber-derived plants. Irrigation with a 60 mm NaCl solution depressed total tuber fresh weight in both seed tuber-(43%) and microtuber-derived plants (75%), but total tuber number was increased (77% and 663%, respectively). This increase in tuber numbers has potential value in the minituber production industry.

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Servet Kefi, M.M. Meagher, P.E. Read, and A.D. Pavlista

The effects of different cytokinin-like compounds on invertase activities at different tuberization stages of potato (Solanum tuberosum L. `Atlantic') were examined. Single nodal segments were cultured on MS medium plus 6% sucrose and supplemented with either 2 mg kinetin/L, 0.1 mg thidiazuron (TDZ)/L, 1.0 mg AC 243,654/L, 0.1 mg AC 239,604/L, or no cytokinin. Tissue samples for determining invertase activity were taken at three stages of tuberization: stage 1, the “hook stage”; stage 2, the “swelling stage”; and stage 3, “tuber initials.” Invertase activity was significantly affected by the interaction between cytokinin-like compounds and tuberization between cytokinin-like compounds and tuberization stages. The highest invertase activities in the stolons at stage 1 were found in kinetin and TDZ treatments. Invertase activity in the stolons on the control medium significantly increased from stage 1 to 2 and decreased at stage 3. Invertase might play a role in either stolon elongation or carbohydrate utilization by increasing the pool of reducing sugars.

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Genhua Niu, Makio Hayashi, and Toyoki Kozai

Potato (Solanum tuberosum L. cv. Benimaru) plantlets were cultured under four lighting cycles (photoperiod/dark period: 16 h/8 h, 4 h/2 h, 1 h/0.5 h, and 0.25 h/0.125 h) photoautotrophically (without sugar in the medium), and photomixotrophically (with sugar in the medium) in vitro for 28 days. Simulations of time courses of CO2 concentration in the vessel (Ci) and dry weight accumulation of the plantlets cultured photoautotrophically were conducted using a previously developed model (Niu and Kozai, 1997). While underestimation and overestimation of time courses of Ci in some treatments were observed, the simulated results of Ci and dry weight accumulation of the plantlets generally agreed with the measured ones. The difference of net photosynthetic rate response to Ci throughout the culture period was examined between the plantlets cultured photoautotrophically and photomixotrophically. Quantitative relationship between daily net photosynthetic rate (daily net production) and vessel ventilation rate per plantlet was simulated under various CO2 levels outside the vessel for given sizes of potato plantlets cultured photoautotrophically in vitro to aid appropriate CO2 enrichment and vessel design in commercial micropropagation.