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Luis A. Valdez-Aguilar, Catherine M. Grieve, James Poss and Michael A. Mellano

flowering stems ( Table 3 ). Table 3. Effect of increasing electrical conductivity (EC) and pH in irrigation water on flowering shoot attributes and tuberous root weight of ranunculus ‘Yellow ASD’ and ‘Pink CTD’ grown in sand tanks. Tuberous root weight

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Jeffery K. Iles and Nancy H. Agnew

Electrolyte leakage and regrowth were measured from September through January to determine cold hardiness of Sedum spectabile × telephium L. `Autumn Joy' and Sedum spectabile Boreau. `Brilliant' plants grown outdoors in central Iowa. Crowns were subjected to 0, –3, –6, –9, –12, –15, –18, –21, –24, or –27C. Regrowth tests were performed on whole crowns and electrolyte leakage was determined on excised tuberous root and crown tissue. Both cultivars were killed at –3C in September, but they acclimated gradually through January. Maximum hardiness was achieved in January, with killing temperatures of –27C for `Autumn Joy' and –21C for `Brilliant'. Regrowth quality ratings were significantly correlated with crown and tuberous root electrolyte leakage measurements, although the relationship was stronger for `Autumn Joy'.

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Jens J. Brøndum and Royal D. Heins

Effects of temperature and photoperiod on growth rates and morphological development of Dahlia pinnata Cav. `Royal Dahlietta Yellow' were determined by growing plants under 45 combinations of day and night temperatures (DT and NT, respectively, and photoperiod. DT and NT ranged from 10 to 30C and photoperiods from 10 to 24 hours·day-1. Photoperiod influenced vegetative development more than reproductive development as plants flowered in all photoperiods. Lateral shoot count and length decreased and tuberous root weight increased as photoperiod decreased from 16 to 10 hours. Temperature interacted with photoperiod to greatly increase tuberous root formation as temperature decreased from 25 to 15C. Increasing temperature from 20 to 30C increased the number of nodes below the first flower. Flower count and diameter decreased as average daily temperature increased. Nonlinear regression analysis was used to estimate the maximum rate and the minimum, optimum, and maximum temperatures for leaf-pair unfolding rate (0.29 leaf pair/day, 5.5, 24.6, and 34.9C, respectively), flower development rate from pinch to visible bud (0.07 flower/day, 2.4, 22.4, and 31.1C, respectively), and flower development rate from visible bud to flower (0.054 flowers/day, 5.2, 24.4, and 31.1C, respectively). The results collectively indicate a relatively narrow set of conditions for optimal `Royal Dahlietta Yellow' dahlia flowering, with optimal defined as fast-developing plants with many large flower buds and satisfactory plant height. These conditions were a 12- to 14-hour photoperiod and ≈ 20C.

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Rozalyn Pama*, Jay Doronila and Mari Marutani

Fifteen sweetpotato [Ipomoea batatas (L.) Lam] accessions grown on Guam were studied for morphological and genetic characteristics. Accessions, obtained from AVRDC (Asian Vegetable Research and Development Center) in Taiwan, Saipan, Rota, and Guam, were investigated for marketable yield, growth habit and characteristics of tuberous roots (color, shape, sugar content and moisture content). Results of this study were used to determine the morphological relationship of the accessions of sweetpotato. Phenetic analysis revealed four major clusters according to tuberous root characteristics. The genetic relationship of these sweetpotato accessions was also evaluated for genetic differences among accessions. DNA was extracted and went through polymerase chain reaction (PCR). PCR products were analyzed by random amplified polymorphic DNA (RAPD) fingerprinting. Result of the genetic relationship among the sweetpotatoes was compared with the morphology of accessions using UPGMA cluster analysis and principal compounds analysis.

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A. Habib, L. D'Aoust and D. Donnelly

Micropropagation of herbaceous peony (Paeonia) cultivars and hybrids (Paula Fay, Cytherea, Prairie Moon, and Sarah Bernhardt) was investigated. Root clumps were removed from the field in February and forced in the greenhouse. Explants were excised buds from the crown area. Culture contamination levels were reduced by selection of crown buds prior to budbreak and disinfestation using combination treatments of 20 min with 5% potassium iodide followed by 10 min with 10% bleach. Genotypes responded differently to adventitious multiplication (Stage II) and tuberous root formation (Stage III) in Murashige and Skoog basal medium supplemented with 6-benzylaminopurine and gibberellic acid (Stage II) or indolebutyric acid (Stage III). Transfer to the greenhouse was accomplished (Stage IV) with a limited number of plants.

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Garry Legnani and William B. Miller

Experiments were conducted to evaluate effects of photoperiod on growth and dry-weight partitioning in Dahlia sp. `Sunny Rose' during both seedling (plug) production and subsequent production in 10-cm pots. Plugs were grown under short days [9-hour natural photosynthetic photon flux (PPF)] or long days (same 9-hour PPF plus a 4-hour night interruption with incandescent light). Total plant dry weight was unaffected by photoperiod; however, long days (LD) inhibited tuberous root development and increased shoot dry weight, fibrous root dry weight, leaf area, shoot length, and number of leaf pairs. Long days reduced plug production time by ≈1 week compared with short days (SD). Following transplanting to 10-cm pots, shoot growth and foliar development were superior under LD. There was no effect of photoperiod on foliar N concentration. The superior growth of LD plugs following transplanting can be attributed to the plant being in a physiological state conducive to shoot expansion instead of storage.

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Seung-Hyun Kim, A.A. De Hertogh and P.V. Nelson

Two experiments were conducted to determine the effects of applied ancymidol, chlormequat, daminozide, paclobutrazol, and uniconazole on early spring (March) and late (May) spring forcing of Dutch-grown Bleeding Heart [Dicentra spectabilis (L.) Lem.] as a flowering pot plant. Most of the plant growth regulator (PGR) treatments delayed flowering, however, the average time to flower after planting was from 17 to 21 days for untreated plants and delays were only 3 to 6 days with PGR treatments. Thus, the effect is not important commercially. Acceptable plant quality and height control not only at flowering but also 14 days later was obtained with two sprays of 3000 mg·L-1 (ppm) daminozide or two sprays of 50 mg·L-1 paclobutrazol. Uniconazole reduced total plant height, however, because the inflorescence did not elongate, plant quality was greatly reduced. Most ancymidol sprays were phytotoxic producing a chlorosis of the leaf margins. Media drenches of ancymidol or chlormequat did not control total plant height. Sprays and media drenches of ancymidol, daminozide, paclobutrazol, and uniconazole produced plants with a very deep green leaf color, but chlormequat did not. The total number of shoots per tuberous root, the number of shoots with flowers, and stem strength were not significantly affected by PGR treatments. If the tuberous roots have been properly cold treated, they initiate growth rapidly after planting. Thus, the first PGR spray must be applied immediately after shoot growth is initiated, which was 6 to 8 days after planting, followed by a second spray 5 days later. Two applications are necessary because of uneven shoot emergence and growth from the tuberous roots.

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Shisheng Li, Qiufang Xiong, Jingcai Li, Yuanping Fang and Jun Xiang

. 1’ resembled that of potherb mustard and differed from that of ‘Wuqing’ ( Fig. 2A–C ), whereas the root of ‘Luoxue No. 1’ was a tuberous root like that of ‘Wuqing’ radish ( Fig. 2D ). Data were collected on the yield of leaves and roots, and hollows

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Wahiba Boutebtoub, Michel Chevalier, Jean-Claude Mauget, Monique Sigogne, Philippe Morel and Gilles Galopin

concentrated ( Fig. 9 ). Several lacticifers can be observed at the edge of the parenchymatous cortex in the form of isolated or grouped cells. The tuberous root is particularly rich in starch ( Figs. 11 and 12 ). Starch grains are present throughout the

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Arthur Villordon, Christopher Clark, Tara Smith, Don Ferrin and Don LaBonte

establishment as the initiation of adventitious roots that can start as early as 3 DAT under field conditions ( Villordon et al., 2009c ). This period corresponds to Togari's (1950) Period I in the early “tuberous-root thickening stage,” defined as the