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Margarita R. Villagarcia, Wanda W. Collins, and C. David Raper Jr.

Soil N availability is an important component in storage root production of sweetpotato [Ipomoea batata (L.) Lam.]. A controlled-environment experiment was conducted to characterize effects of N availability on patterns of dry matter, nonstructural carbohydrates, and N accumulation, and to determine possible components of N use efficiency that vary between two genotypes of sweetpotato. Rooted cuttings of `Jewel' and MD810 were transplanted into pots filled with sand and kept in a growth chamber for 72 days. Plants were watered during the first 30 days with a complete nutrient solution that contained 14 mm NO3 - and then for the next 42 days with one of three complete nutrient solution that contained either 2, 8, or 14 mm NO3 -. At 30, 44, 58, and 72 days after transplanting, three plants from each cultivar and treatment combination were sampled and separated into leaves, stems plus petioles, fibrous roots, and storage roots. Each plant fraction was freeze-dried, weighed, ground, and analyzed for total N, soluble sugars, and starch. Availability of N in the substrate, which limited dry matter accumulation at 2 mm NO3 -, was nonlimiting at 8 and 14 mm NO3 -. In both genotypes, net assimilation rate, efficiency of N use (i.e., increments of dry matter accumulated per increment of N taken up), and proportion of dry matter allocated to storage roots were greater for N-stressed (2 mm NO3 -) than N-replete (8 and 14 mm NO3 -) plants. For the N-stressed plants, however, efficiency of N use was greater in MD810 than in `Jewel'. Although rate of NO3 - uptake per unit fibrous root mass was similar in the two genotypes under the N stress treatment, MD810 had greater uptake rate than `Jewel' under nonlimiting availability of NO3- in the substrate. The increased rate of uptake under nonlimiting NO3 - supplies apparently was related to enhanced rates of carbohydrate transport from shoots to roots. As tissue concentration of N declined in response to the lowest application of NO3 -, shoot growth was limited prior to, and to a greater extent than, the photosynthetic rate. The resulting relative decline in sink activity of shoots thus presumably increased the availability of carbohydrates for transport to roots.

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Helen Beaufort-Murphy

Yield and insect damage of 50 potato cultivars, representative of genetic variation found in CIP germplasm collection, were evaluated over two years in a wide range of environmental conditions throughout Peru, from 4°S to 17°S, including coastal desert, cool highland and humid jungle, at altitudes from 180m to 3280m. Storage root and foliage yields were related to maximum and minimum temperature, photoperiod, precipitation, soils, and insect damage. Genotypic yield varied considerably from one location to another. Jonathan (Peruvian cultivar) produced well in Cañete (coastal desert) but not in the jungle or highlands. Jewel (US cultivar) produced well in Yurimaguas (jungle) but not in coastal deserts. Pesticides were not used but several cultivars had little or no insect damage, others were badly damaged. Some cultivars produced a reasonable yield over a wider range than did others. Results suggest that a cultivar can be strongly adapted to a particular set of environmental conditions. Data provide valuable information for growers-breeders.

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W. E. Healy and H. F. Wilkins

Abstract

When Alstroemeria ‘Regina’ shoots were grown in a continuous 13°C air temperature, and the underground structures (rhizomes and roots) were placed in a 5°, 10°, 15°, 20°, or 25° water bath, plants produced 22%, 33%, 13%, 14%, or 5% generative shoots, respectively (Expt. 1). When the underground structures were grown at 13°, there were no differences in percentages of generative shoots, regardless if shoots were in a 13° or 21° air temperature, and regardless if shoots were under short or long photoperiods. When soil temperature was 21° and air temperature was 13°, 12% generative shoots were produced only with a night interruption photoperiod (Expt. 2). Data from these 2 experiments led us to conclude that floral induction was controlled primarily by temperatures to which the underground structures were subjected, regardless of the air temperature or photoperiod. Storage root and rhizome dry weights were promoted by 13° air, 13° soil temperatures and night interruptions with incandescent light. Treatments which had a high percentage of generative shoots also had high root and rhizome dry weights.

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J. E. Wyatt

Abstract

Worldwide interest in the winged bean [Psophocarpus tetragonolobus (L.) D.C.] as a food legume has increased in the past decade (6). The crop has the potential for greatly improving human nutrition needs in the tropics due to the relatively high protein content of the seeds (30–42%) and tuberous roots (8–20%, dry weight basis) and the fact that all plant parts except the stem are edible (4). It also is grown as a cover crop or green manure crop and is useful for livestock feed (5).

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Susan C. Miyasaka, Marisa Wall, Don LaBonte, and Alton Arakaki

( Follett, 2006 )]. Sweetpotato weevil larvae feed and develop within the storage root of sweetpotato, making it difficult to control the larvae with insecticides and resulting in inedible storage roots ( Thompson et al., 1999 ). Crop losses in Hawai‘i due

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Peter J. Dittmar, Jonathan R. Schultheis, Katherine M. Jennings, David W. Monks, Sushila Chaudhari, Stephen Meyers, and Chen Jiang

to North Carolina growing conditions, producing high yielding and high quality storage roots ( Yencho et al., 2008 ), and because of its adaptability is grown on more than 88% of the commercial acreage across the state ( Schultheis, 2016

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G. Craig Yencho, Kenneth V. Pecota, Jonathan R. Schultheis, Zvezdana-Pesic VanEsbroeck, Gerald J. Holmes, Billy E. Little, Allan C. Thornton, and Van-Den Truong

. 1998. A single cutting was taken from each seedling and planted in the field in May 1998 in an “on-farm” trial and selected as a “single-hill selection” on 9 Sept. 1998. A “single-hill selection” includes the storage roots derived from the single plant

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Christopher A. Clark, Washington L. da Silva, Ramón A. Arancibia, Jeff L. Main, Jonathan R. Schultheis, Zvezdana Pesic van-Esbroeck, Chen Jiang, and Joy Smith

batatatis ( da Silva and Clark, 2012 ; Stokes et al., 2012 ). These fungi have also been isolated frequently from symptomless transplants and storage roots and it appears that infection is not a limiting factor to the development of this disease complex

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Susan C. Miyasaka, Sharon Motomura-Wages, Ishakh Pulakkatu-Thodi, Michael J. Melzer, Christopher A. Clark, Don R. LaBonte, and Arthur Q. Villordon

and C ‘Okinawan’ were similar in morphological and agronomic traits (e.g., shape of leaves and appearance and taste of storage roots). The LSU AgCenter sweetpotato cultivar LA 08-21p is an advanced line with total yield at 80% of commercial cultivar

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David Wees, Philippe Seguin, Josée Boisclair, and Chloé Gendre

Croatia found that using rooted cuttings or transplants instead of slips led to higher yields and larger storage roots. The larger initial root mass on rooted cuttings may encourage faster early growth compared with that obtained with slips ( Novak et al