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Sergey Nesterenko and Kenneth C. Sink

Lutein and zeaxanthin are becoming established as carotenoids beneficial for protection against common age-associated eye diseases. Thus, 15 potato (Solanum tuberosum subsp. tuberosum L.) breeding lines, cultivars Atlantic, Spunta, and Yukon Gold; and orange flesh OR-4 were surveyed for carotenoid profiles. Seven carotenoids, including violaxanthin, neoaxanthin, antheraxanthin, lutein, zeaxanthin, β-cryptoaxanthin, and β-carotene, were identified in the 19 genotypes. Violaxanthin and lutein were the prominent carotenoids detected in all genotypes studied. Neoaxanthin and antheraxanthin were found in 26% and 63% of the genotypes, respectively. β-Cryptoaxanthin, zeaxanthin, and β-carotene were found in only 5%, 10%, and 16% of the genotypes, respectively. Lutein varied from 19.8 to 119.0 μg·100 g-1 fresh weight across the 15 white- or yellow-flesh breeding lines. In contrast, zeaxanthin was detected at a low level in only one breeding line and at high level in OR-4. The three cultivars had profiles typical of yellow-flesh potatoes `Spunta' and `Yukon Gold'; while `Atlantic' had a typical white-flesh profile and a trace of zeaxanthin. The carotenoid baseline data established in this study provide information for activities to enhance potato for lutein and zeaxanthin.

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Kathleen G. Haynes

Although potato (Solanum tuberosum L.) tuber yellow flesh per se is known to be controlled by a single gene, the intensity of yellow flesh varies widely in Solanum L. species. Many diploid species have very intense yellow flesh, as compared to the commercial tetraploid yellow-flesh cultivar `Yukon Gold'. Inheritance of yellow-flesh intensity at the diploid level was investigated in a hybrid population of S. phureja ssp. phureja (Juz. & Buk.)-S. stenotomum ssp. stenotomum (Juz. & Buk.) (PHU-STN). Six randomly chosen male parents were crossed to five randomly chosen female parents in a Design II mating scheme. In 1993, ≈12 progeny (clones) from each of the 30 families were planted in a randomized complete block design with two replications in Presque Isle, Maine, and evaluated for tuber yellow-flesh intensity as measured by a reflectance colorimeter. Twenty-five tubers from each plot were scored using the YI E-313 yellow intensity scale. An average YI E-313 score was obtained for each plot. Narrow-sense heritability on a plot mean basis was estimated as 0.99 with a SE of 0.65 to 0.72. There were significant differences among clones within a family. Results suggest that rapid progress can be made in breeding for intense yellow flesh in this diploid population. Clones from this population that produce 2n gametes represent an important source of germplasm for enhancing the intensity of the yellow-flesh trait in tetraploid potatoes.

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Björn H. Karlsson and Jiwan P. Palta

Recent studies suggest cold-regulated heat-stable proteins mitigate the potential damaging effects of low water activity associated with freezing. A proposed function of these proteins is stabilization of enzymes during exposure of plants to subzero temperatures. To test this hypothesis for tuber-bearing Solanum L. species we determined the quantitative expression of heat-stable proteins, the qualitative changes in dehydrin proteins, and the capacity of heat-stable proteins to cryoprotect a freeze-thaw labile enzyme lactate dehydrogenase (LDH). We used five tuber-bearing Solanum species (S. tuberosum L. `Red Pontiac', S. acaule Bitter, S. sanctae rosea Hawkes, S. commersonii Dunal, and S. cardiophyllum Bitter), which vary in nonacclimated relative freezing tolerance (NA RFT), acclimated relative freezing tolerance (AC RFT), and acclimation capacity (ACC). The protein fraction containing a mixture of heat-stable proteins demonstrated cryoprotective capacities greater or equal to other cryoprotective compounds (bovine serum albumin, polyethylene glycol, glycerol, and sucrose). Heat-stable proteins extracted from acclimated S. commersonii had superior cryoprotective capacity than those extracted from nonacclimated S. commersonii plants. Interestingly, in the presence of these proteins extracted from acclimated plants (in S. commersonii and S. sanctae rosea), LDH activity was elevated above that of unfrozen controls. No quantitative relationships were found between heat-stable protein concentration and NA RFT, AC RFT, or ACC among the five species. This was also true for dehydrin protein expression. Cold acclimation treatment resulted in increased dehydrin expression for acclimating and nonacclimating species. In three of the cold acclimating species (S. acaule, S. sanctae rosea, and S. commersonii), an increase in dehydrin expression may play a role in increased freezing tolerance during cold acclimation. In the cold sensitive, nonacclimating species (S. tuberosum and S. cardiophyllum), however, an increase in dehydrin level maybe related to the response of these species to changed (perhaps stressful) environment during cold treatment. By exploiting the genetic variation in NA RFT and ACC for five tuber-bearing species, we were able to gain new insight into the complexity of the relationship between heat-stable protein and cold response.

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John W. Scott

Standardized phenotyping is being used in tomato (Solanum lycopersicum) and potato (S. tuberosum) as part of the USDA-funded Solanaceae coordinated agricultural project (SolCAP). In tomato, a panel of 480 lines, 144 fresh market, 144 processing, 44 vintage lines, 48 landraces, and 101 related Solanum species accessions, are being grown over two seasons at multiple locations. These tomato genotypes will also be screened for over 7600 single nucleotide polymorphism markers that are being developed. Characters being phenotyped are hypocotyl color, plant habit, inflorescence (simple or compound), flower fasciation, flowering time, time to maturity, size of blossom scar, and pedicel type (jointless or jointed). Transverse and equatorial cross-sections of fruit are also being scanned to obtain measures of fruit shape and color by tomato analyzer computer software. Other fruit characters being measured are pH, titratable acidity, and soluble solids. Some useful information may come from this phenotyping and genotyping effort. However, in this author's opinion, the value of measuring some of the traits is very limited in the face of much more important breeding traits that are difficult to fit into a standardized phenotyping format. For instance, proper assessment of several fruit disorders is not being attempted, but such data might yield some invaluable marker information. Part of this is the result of funding limitations for the phenotyping effort. However, a major benefit of the SolCAP analysis will be the development of markers that will differentiate the lines being studied, because there is a present lack of polymorphisms in tomato germplasm where wild species introgressions are minimal or distant in time. This will allow breeders to proactively select for recurrent parent backgrounds in backcrossing projects and may aid in the identification of associations of markers with important characteristics. As one looks to the future of standardized phenotyping, there are some important traits that will be difficult to phenotype such as tomato flavor, which is quite subjective and for which there are no good objective measures.

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M. Moriondo, M. Bindi, and T. Sinclair

Crop growth simulation models have been mainly developed to simulate final yield reliably. Thus, a main challenge in these models is the definition of a stable method for expressing the growth of harvested organs (e.g., fruit, seed, tuber, etc.). Generally, two approaches have been used: growth rate analysis of harvested organs [yield growth rate (YGR)] and analysis of harvest index (HI) increase over time (dHI/dt). This work aims to: 1) examine whether YGR and dHI/dt increase linearly over much of growing period, and 2) compare the two growth indices in terms of stability across a number of treatments, in order to identify which is the best indicator of harvest-organ growth. This analysis has already been performed for a large number of field crops, including wheat (Triticum aestivum L.), sunflower (Helianthus annuus L.), soybean [Glycine max L. (Merr.)], and pea (Pisum sativum L.), but it has never been attempted in crops where final yield is not simply seeds. In this study, YGR and dHI/dt performances for tomato (Lycopersicum esculentum Mill.), potato (Solanum tuberosum L.), and eggplant (Solanum melongena L.) were compared using 21, 18, and 4 datasets, respectively. Results indicated that both descriptors of harvest-organ growth increased linearly for most of the growth period, whilst the comparison among the two variables in terms of stability showed that, although a direct statistical test failed, dHI/dt was more suitable to describe harvest-organ growth (smaller coefficient of variability) under a large range of crop management conditions (e.g., irrigation, sowing date, planting density, and water salt concentration).

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

Colorado potato beetle (Leptinotarsa decemlineata Say) is the leading insect pest of potato (Solanum tuberosum L.) in northern latitudes. Host plant resistance is an important tool in an integrated pest management program for controlling insect pests. Field studies were conducted to compare natural host plant resistance mechanisms (glandular trichomes and Solanum chacoense Bitter-derived resistance), engineered [Bacillus thuringiensis (Bt) Berliner Bt-cry3A], and combined (glandular trichomes + Bt-cry3A and S. chacoense-derived resistance + Bt-cry3A transgenic potato lines) sources of resistance for control of colorado potato beetle. Six different potato clones representing five different host plant resistance mechanisms were evaluated for 2 years in a field situation under natural colorado potato beetle pressure in Michigan and New York, and in a no-choice field cage study in Michigan. In the field studies, the S. chacoense-derived resistance line, Bt-cry3A transgenic, and combined resistance lines were effective in controlling defoliation by colorado potato beetle adults and larvae. Effectively no feeding was observed in the Bt-cry3A transgenic lines. The glandular trichome line suffered less defoliation than the susceptible control, but had greater defoliation than the Bt-cry3A transgenic lines and the S. chacoense-derived resistance line. In the no-choice cage study, the Bt-cry3A transgenic lines and the combined resistance lines were effective in controlling feeding by colorado potato beetle adults and larvae with no defoliation observed. The S. chacoense-derived resistance line and the glandular trichome line suffered less defoliation than the susceptible control. Based on the results of the field trials and no-choice field cage studies, these host plant resistance mechanisms could be used to develop potato varieties for use in a resistance management program for control of colorado potato beetle.

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Noël E. Pallais, Nelly Y. Espinola, Rosario M. Falcon, and Ruperto S. Garcia

Sexual seeds of potato (Solanum tuberosum L.) usually emerge poorly under high-temperature conditions (> 25 C). A seedling vigor study was conducted during the warm season (1988-89) in Lima, Peru, and the results of two representative tests. are reported. Two presowing treatments and a rinsed control were compared for seedlingstand establishment in a screenhouse with old (>18 months) and new (> 6 months) sexual seeds of three potato crosses. The treatments consisted of soaking the seed in solutions of KN03 + K3P04 at – 1.0 MPa (priming) and gibberellic acid at 1500 ppm (GA1500). Seedling vigor was lower at 34C (February test) than at 29C (November test). In both tests, overall seedling performance was highest in seed of the cross Atlantic × LT-7. Old seed was more vigorous than new seed, particularly when the crosses Atzimba × R128.6 (B2) and Serrana × LT-7 (Cl) were tested at 34C. Priming increased percentage of early (10 days) emergence over the other treatments at 34C and increased seedling dry weight in both tests. GA1500 increased percentage of final (17 days) emergence in crosses B2 and Cl, as compared to rinsing, except at 29C, where there were no significant differences in old seed. For sowing true potato seed at high temperature, a) the genotype is a crucial factor, b) sufficient seed storage (> 18 months) may be essential, and c) seed priming is more effective than the standard GA1500 treatment.

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H.L. Bhardwaj, A.S. Bhagsari, and K.G. Haynes

Two experiments, each with 100 (Solanum tuberosum L.) genotypes, were planted to compare fall-planted (August 22, 1988) crop with spring-planted (March 14, 1989) crop and to identify high yielding genotypes for each planting. Significant variation for tuber yield, 90-100 days after planting, was observed in both experiments. The mean yield of spring planting (25.8 Mg/ha with a range of 9.8 to 49.5 Mg/ha) was significantly higher than mean yield of fall-planting (18.2 Mg/ha with a range of 8.5 to 30.2 Mg/ha). The five highest yielding genotypes in fall planting were: B-0245-15, B-0175-2, B-0242-2, Kennebec, and Norchip whereas the five highest yielding genotypes in spring planting were: B-0180-36, B-9792-88, B-0179-17, B9988-7, and Belchip.

An additional split-split-plot experiment with 4 replications was initiated March 14, 1989 to identify optimum rate of N fertilizer and spacing within rows. This experiment consisted of three Nitrogen levels (0, 125, and 250 kg/ha), three genotypes (Atlantic, Kennebec, and La Rouge), and two spacings between plants (10 and 20 cm). All plots received 120 kg P and 170 kg K/ha. Data showed that N rates of 125 Kg/ha and 250 kg/ha gave identical tuber yields (50 Mg/ha). Closer spacing of 10 cm within rows resulted in significantly higher tuber yield (46 Mg/ha) as compared to 20 cm spacing (33 Mg/ha).

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N.C. Yorio, C.L. Mackowiak, R.M. Wheeler, and J.C. Sager

Potato (Solanum tuberosum L. cvs. Norland and Denali) plants were grown under high-pressure sodium (HPS), metal halide (MH), and blue-light-enhanced SON-Agro high-pressure sodium (HPS-S) lamps to study the effects of lamp spectral quality on vegetative growth. All plants were initiated from in vitro nodal cultures and grown hydroponically for 35 days at 300 μmol·m–2·s–1 photosynthetic photon flux (PPF) with a 12-hour light/12-hour dark photoperiod and matching 20C/16C thermoperiod. `Denali' main stems and internodes were significantly longer under HPS compared to MH, while under HPS-S, lengths were intermediate relative to those under other lamp types, but not significantly different. `Norland' plants showed no significant differences in stem and internode length among lamp types. Total dry weight of `Denali' plants was unaffected by lamp type, but `Norland' plants grown with HPS had significantly higher dry weight than those under either HPS-S or MH. Spectroradiometer measurements from the various lamps verified the manufacturer's claims of a 30% increase in ultraviolet-blue (350 to 450 nm) output from the HPS-S relative to standard HPS lamps. However, the data from `Denali' suggest that at 300 μmol·m–2·s–1 total PPF, the increased blue from HPS-S lamps is still insufficient to consistently maintain short stem growth typical of blue-rich irradiance environments.

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

Potatoes (Solanum tuberosum L.) have been grown successfully with a recirculating nutrient film technique (NFT) when a fresh nutrient solution is used for each planting. During the past year, we conducted two studies in which the same nutrient solution was used for successive plantings (EC and pH were maintained at 0.12 S·m–1 and 5.8). Results showed that successive plantings became prematurely induced (tubers initiating near 20 days after planting–DAP), causing stunted shoot growth and reduced yields per plant. When “old” nutrient solution from a continuous production system was regularly added to a newly started plant system maintained under a non-inductive environment (12-h photoperiod with night break of 6 h into dark), tubers formed on “old” nutrient solution plants (24 DAP), but not on “new” solution plants. When charcoal water filters were placed on the systems, plants grown on either “old” or “new” nutrient solutions showed no tuber initiation (plants harvested at 42 DAP). Results suggest that a tuber-inducing factor(s) emanating from the plants accumulates in the nutrient solution over time and that the factor(s) can be removed by charcoal absorption.