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Jericó J. Bello-Bello, Adriana Canto-Flick, Eduardo Balam-Uc, Eunice Gómez-Uc, Manuel L. Robert, Lourdes G. Iglesias-Andreu, and Nancy Santana-Buzzy

investigations on the species of this genus. The aim of this study was to evaluate the effect of the age of the explant, the composition of the culture medium, and a temporary immersion culture system on shoot proliferation and elongation. Material and

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Wen-Hao Sun and Roy K. Nishimoto

The effect of single and daily alternating temperature cycles on elongation of emerged buds of purple nutsedge (Cyperus rotundus L.) was characterized to determine whether shoot elongation responded to alternating temperature as a thermoperiodic function. Glasshouse-grown tubers with emerged buds of 2 to 5 mm in length were used in experiments. Shoot extension increased at 35 °C after 7 days, but no significant shoot extension occurred at all other constant temperatures of 20, 25, 30, 40, and 45 °C. However, 2- to 8-fold increases in shoot extension occurred at alternating temperatures of 25/15, 30/20, 35/25, 40/30, 41/35, 42/38, and 45/35 °C (12/12 hours) as compared to the respective mean constant temperatures. Daily temperature differences of 2 and 4 °C did not stimulate shoot elongation, while temperature differences of 8 and 12 °C caused an 8-fold shoot stimulation when compared to the 24 °C constant temperature. Shoot elongation increased with increasing numbers of alternating temperature cycles. The optimal duration of the lower and upper temperature phases differed depending on temperature regimes; at 40/30 °C, maximal elongation occurred with daily exposures of 40 °C for 1 to 3 hours and 30 °C for 23 to 21 hours respectively, while at 30/20 °C, maximal elongation occurred with daily exposures of 30 °C for 15 hours and 20 °C for 9 hours. These results suggest that elongation of purple nutsedge tuber buds responds to alternating temperature as a thermoperiodic function.

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Fang Geng, Renae Moran, Michael Day, William Halteman, and Donglin Zhang

are commonly used as explants for in vitro propagation of apple ( De Klerk, 1992 ). Efficient propagation using this method depends on rapid shoot development and elongation following establishment. However, many important apple rootstock cultivars

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Sven E. Svenson

Rooting and growth of Verbena cuttings (Verbena × hybrids Voss) were measured to determine response to foliar-applied benzylaminopurine (BA). There was no rooting response to BA application when visible nodal roots were present at the base of the cutting. There was no response to 30, 100, or 300 mg BA/liter applied to the foliage 48 or 96 hours after excision from the stock plant. Rooting-zone dry mass, total cutting dry mass, and number of roots were increased by 30 mg BA/liter applied immediately after excision when there were no visible nodal roots at the base of the cuttings. Foliar application of BA at 10 or 30 mg·liter-1 increased lateral bud elongation of subsequently rooted shoots by 20% and 49%, respectively. Application of BA during cutting propagation to enhance subsequent lateral bud elongation does not appear to inhibit rooting in Verbena stem cuttings. Chemical name used: 6-benzylaminopurine (BA).

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David J. Ballantyne

In a greenhouse experiment involving 13 hardy azalea (Rhododendron spp.) cultivars, `Noordthiana' and `Treasure' had the highest rate of shoot elongation and the highest photosynthetic capacity (Pcap) during the summer. In winter, `Treasure' had a high rate of shoot elongation and Pcap, but `Noordthiana' had a high rate of shoot elongation and low Pcap. Long days or GA3 sprays stimulated shoot elongation but not Pcap of certain cultivars. GA3 was effective in stimulating shoot elongation of `Vuyk's Scarlet' if plants were given supplemental photoperiods under natural winter (short) photoperiods. Cultivars with a high rate of shoot elongation and Pcap likely will produce salable plants in a shorter time period than slower growing cultivars because less time elapses between prunings. Production time can be decreased further with GA3 sprays, especially with GA3 applications in combination with supplemental photoperiods during the short days of winter. Chemical name used: gibberellic acid (GA3).

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P.R. Fisher, J.H. Lieth, and R.D. Heins

Stem elongation of commercially produced flowering poinsettia (Euphorbia pulcherrima L.) is often sigmoid. However, sigmoid mathematical functions traditionally used for representing plant growth fail to adequately describe poinsettia stem elongation when a shoot has a long vegetative growth period. A model was developed that explicitly described three phases of poinsettia stem elongation: 1) the initial lag phase, where stem length increases approximately exponentially; 2) a period when elongation is linear; and 3) a plateau phase, where elongation rate declines to zero and stem length reaches an asymptotic maximum length. The timing of the plateau phase was linked to flower initiation date. Fit of the resulting model to data from single stem `Freedom' poinsettia grown with different periods between transplant and flower initiation had an R2 of 0.99. Model parameters had clear biological meaning, and the poinsettia model has horticultural application for simulation and graphical tracking of crop height.

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Samir C. Debnath

The effects of TDZ (0, 0.1, 1, 5 and 10 μm) and explant orientation on adventitious shoot regeneration of `Erntedank' lingonberry were studied. Moderate concentration (1 to 5 μm) of TDZ supported bud and shoot regeneration, but strongly inhibited shoot elongation. TDZ initiated cultures were transferred to medium containing 1-2 μm zeatin and produced usable shoots after one additional subculture. Adventitious bud and shoot regeneration was greatly influenced by explant orientation. Elongated shoots were rooted on a 2 peat: 1 perlite (v/v) medium, and the plantlets were acclimatized and eventually established in the greenhouse with 80% to 90% survival rate.

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J. Jiao, X. Wang, and M.J. Tsujita

Uniconazole was applied as a drench or spray to six hybrid lily (Liliurn sp.) cultivars. Spray application was generally more effective than drench in reducing shoot elongation rate in the first few weeks, and then the efficacy decreased and was less effective than the drench at later stages of plant development. At flowering, a uniconazole drench at 0.1 mg/pot was ineffective for height reduction in `Bravo', `Juliana', and `Sunray' lilies. At higher rates, uniconazole drench was similar to spray in reducing shoot growth in `Bravo' and 306-1 but less effective than spray in `Juliana', `Star Gazer', and `Sunray' lilies. Uniconazole spray reduced plant height at flowering in all the lilies compared to control plants. Days to flower was not affected in `Bravo', `Juliana', and `Sunray' but was increased in `Star Gazer', 306-1, and 306-2 by uniconazole spray treatments. Flowering duration was decreased only in 306-1 by uniconazole spray at 0.2 mg/pot. Chemical name used: (E)-1-(4-chlorophenyl) -4,4 -dimethyl-2-(l,2,4 -triazol-1-yl)-1-penten-3 -ol (uniconazole).

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Samir C. Debnath

In an attempt to improve the micropropagation protocol for lingonberry (Vaccinium vitis-idaea L.) developed at the Centre, two lingonberry clones were compared for in vitro shoot proliferation on two different media supplemented with varying levels of thidiazuron (TDZ). TDZ supported proliferation at low concentrations (0.1 to 1 μm) but inhibited shoot elongation. However, usable shoots were obtained within 4 weeks by transferring shoot cluster to medium containing 1 μm zeatin. Genotypes differed significantly with respect to multiplication rate with `EL1' producing the most shoots per explant. In both genotypes, shoot proliferation was greatly influenced by explant orientation. Changing the orientation of explants from vertically upright to horizontal increased axillary shoot number, but decreased shoot height and leaf number per shoot. Proliferated shoots were rooted on a 2 peat: 1 perlite (v/v) medium, and the plantlets were acclimatized and eventually established in the greenhouse.

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Azusa Sato, Hiroshi Okubo, and Kazuyuki Saitou

The aim of this study was to investigate physiological and biochemical mechanisms of shoot elongation after cold period in hyacinth (Hyacinthus orientalis L. cv. Delft Blue). Hyacinth shoot rapidly elongated during hydro-culture period in cooled bulbs, but not in non-cooled bulbs. Alpha-amylase (EC 3.2.1.1.) is a key enzyme involved in starch hydrolysis. Alpha-amylase activity increased during the cold storage period and was low during rapid shoot elongation in hyacinth. In the non-cooled bulbs, its activity remained at the similar level. Sucrose content increased during the cold storage period in the shoot, but not in the scales. We, for the first time, isolated cDNA for cold-responsive alpha-amylase gene (HoAmy1A, accession No. AB198975) from hyacinth, and presented that HoAmy1A expression increased in the scale during the cold storage period, but the level was very low during shoot elongation. We also found that promoter region of HoAmy1A contained CArG element, which is related to the response to low temperature. In tulip (Tulipa genesriana L.), the most studied bulbous plant, dramatic increase in alpha-amylase activity and translocation of sugars from the scales to shoot occurred during the growth stage, following cold treatment (Komiyama et al., 1997; Lambrechts et al., 1994). Our results suggest that there are two types (tulip and hyacinth types) of sprouting mechanisms in bulbous plants.