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Open access

Dennis P. Stimart and Peter D. Ascher

Abstract

Bulblets from bulb-scale explants of Lilium longiflorum Thunb. cvs. Ace and Nellie White cultured in darkness on a semisolid Linsmaier-Skoog medium supplemented with 0.03 mg/liter α-naphthalene-acetic acid (NAA) bore no leaves when produced in vitro at constant 30°C but often did when produced at constant 25°. In vitro temperature regimes involving both 25 and 30° resulted in the largest number of leaves per explant. Time in vitro in each temperature regime was calculated to provide equal heat units so that differences could not be explained by a linear relationship between development and temperature × time. Physiological state of explants, measured by time lily bulbs were stored at 4° before tissue culture, interacted with in vitro temperature. Explants from bulbs stored 110 days or less produced significantly fewer but significantly larger bulblets at constant 25° as compared to constant 30°. This difference was not apparent when explants were taken from bulbs stored at 4° more than 110 days. In an experiment with explants from bulbs stored 80 days, there was no significant difference between ‘Ace’ and ‘Nellie White’ in number of scales per bulblet at either 25 or 30° but bulblets of both cultivars contained significantly fewer scales if generated at 30°. Mean width of meristems in ‘Ace’ bulblets was significantly greater when produced in vitro at 30°. Neither initiation of bulblets nor bulblet development appeared controlled by apical dominance.

Open access

Dennis P. Stimart, Peter D. Ascher, and Harold F. Wilkins

Abstract

Up to 50% of bulblets generated in vitro at 30°C from bulbscale explants of Lilium longiflorum ‘Ace’ produced an elongated axis in the 14 weeks after removal from tissue culture and potting in vermiculite. None of the ‘Ace’ bulblets produced in vitro at 25° and none of the ‘Nellie White’ bulblets produced in vitro at either 25° or 30° formed an elongated axis. Increased length of time that ‘Ace’ bulbs were stored at 4° before explanting as well as immersing bulblets generated in vitro at 30° in water at 45° for 1 hour before potting increased the percentage of bulblets with an elongated axis. Axis elongation was not related to bulblet size or to position of scale used for explanting (inner vs. outer bulb scale). Exposing ‘Ace’ bulblets generated at 30° to 3 or more weeks at 4° reduced the percentage of bulblets with an elongated axis to zero. Treatment of chilled bulblets for 2 hours in water at 45° did not reverse the effect of cold.

Open access

Thomas H. Boyle and Dennis P. Stimart

Abstract

Zinnia elegans Jacq. ‘Carved Ivory’, ‘Cherry Ruffles’, and ‘Rosy Future’ were grown under short days (SD) or long days (LD) to determine the effect of photoperiod on flower initiation and morphological development. Plants grown under LD (14, 16, 18, or 24 hours) were greater in height, leaf size, flower diameter, and node number and flowered later compared to plants grown under SD (8, 10, or 12 hours). The greatest increases in plant responses occurred between 12- and 14-hour treatments. Supplemental irradiation (day continuation, night break, and predawn lighting) resulted in LD responses but did not equally affect days to flowering, stem diameter, or node number. Height and ray petal number were greatest for all cultivars under day continuation and flower diameter was largest under day continuation and predawn lighting. More LD before SD resulted in increases in height, stem and flower diameter, node number, ray petal number, and days to flowering, indicating a cumulative effect of LD on morphological development. Results demonstrate that Z. elegans is a facultative SD plant for floral initiation and development and that photoperiodic responses vary between genotypes.

Open access

Thomas H. Boyle and Dennis P. Stimart

Abstract

Irrigation interruptions of 0, 2, 4, or 8 weeks were imposed on actively growing ‘Red Lion’ amaryllis (Hippeastrum × hybridum) bulbs to determine the influence of water stress on flowering. Withholding irrigation for 4 or 8 weeks was effective in promoting early flowering of first and second scapes compared to continuously irrigated plants. Irrigation interruptions of 2, 4, or 8 weeks resulted in first scape flowering on all plants by 160, 140, or 60 days, respectively, after resumption of irrigation. Only 83% of continuously irrigated plants flowered within 160 days. Water stress treatments did not influence total number of flowering scapes per plant produced in 160 days nor number of flowers per umbel. Irrigation interruption affected timing of flowering by promoting scape extension and floral development.

Open access

Dennis P. Stimart and James F. Harbage

Abstract

In vitro shoot proliferation of Pyrus calleryana Decne. ‘Bradford’ was investigated on medium containing BA at 0, 1, 2, 10, or 20 µM in factorial combination with IBA at 0, 0.5, or 5.0 µM. Shoot proliferation increased as BA level increased but the magnitude was reduced as IBA level increased. Greatest shoot proliferation was on medium excluding IBA. Shoots were longest on medium containing 1 or 2 µM BA. Medium with 2 µM BA and 0.5 µM IBA was optimum for shoot proliferation and length. Shoot fasciation increased as BA level increased, but addition of IBA to BA reduced fasciation. Rooting of microcuttings with IBA and sucrose was unsuccessful. Chemical names used: N-(phenylmethyl)-1H purin-6-amino (BA); 1H-indole-3-butanoic acid (IBA).

Open access

Dennis P. Stimart and James F. Harbage

Abstract

Stem pieces from expanding spikes of Liatris spicata (L.) Willd. were cultured in vitro on a Murashige and Skoog medium containing BA to establish proliferating cultures for use in comparing BA and IBA effects on shoot proliferation. Both compounds promoted multiple shoot development. The optimum level for micropropagation was 2.7 μm BA without IBA. Greatest rooting was at 5.0 μm IBA without BA.

Open access

Michael A. Goodman and Dennis P. Stimart

Abstract

Propagation time, N, and shoot growth were studied for their effects on overwinter survival of newly rooted stem tip cuttings of Acer palmatum Thunb. ‘Blood-good’ and Cornus florida L. var. rubra. Propagation of A. palmatum and C. florida in May and June, respectively, resulted in a greater number of plants with shoot growth after rooting compared to those propagated later. Removal of a terminal leaf on A. palmatum after rooting increased the percentage of plants with shoot growth. Nitrogen application after rooting decreased survival before winter storage for A. palmatum propagated in May and C. florida propagated in June and July. May propagation of A. palmatum reduced overwinter survival, whereas propagation date did not affect overwintering of C. florida significantly. Plants with shoot growth and not given N had best overwinter survival, followed by plants with shoot growth given N. Poorest overwintering occurred on both species given N that failed to grow prior to winter storage. Nitrogen application to these plants when newly propagated should be avoided until the role of N is better understood.

Open access

James F. Harbage and Dennis P. Stimart

Abstract

Callus culture establishment and adventitious shoot development from callus of Rhododendron × ‘Gibraltar’ (G) and R. × ‘Old Gold’ (OG) after serial subculture were determined. Callus grew on Anderson's Rhododendron medium containing 2,4- D at 0.0045, 0.009, or 0.018 mm, but was optimum at 0.018 mm, since shoot organogenesis was suppressed at that level. After two callus subcultures, adventitious shoot development from callus on media containing 0, 0.017, 0.034, 0.068, or 0.136 mm zeatin (mixed isomers) was optimum at 0.034 and 0.068 mm zeatin for G and OG, respectively. After 17 weeks (five subcultures), 70- to 75-mg pieces of G and OG callus regenerated ≈20 shoots each. Adventitious shoot regeneration from callus declined with prolonged callus subculture. Regenerated plants are currently being evaluated for somaclonal variation. Chemical names used: (2,4-dichlorophenoxy)acetic acid (2,4-D); (E)-2-methyl-4-(1H-purin-6-ylamino)-2-buren-1-ol (zeatin).

Open access

Dennis P. Stimart, Dennis J. Brown, and Theophanes Solomos

Abstract

Postharvest flower fresh weight of Zinnia elegans Jacq. increased when held in solutions containing 200 mg liter-1 8-hydroxyquinoline citrate (8-HQC) and sucrose and decreased when held in deionized water. Ethylene biosynthesis was enhanced by holding flowers in solutions of 8-HQC + 1, 2% or 3% sucrose compared with deionized water where ethylene release was low initially and remained low. Carbon dioxide evolution declined sharply the first 2 days postharvest and remained low for flowers held in deionized water, but remained at initial levels for those held in 200 mg liter-1 8-HQC + 3% sucrose. Glucose, fructose, and sucrose in ray florets declined to levels barely detectable if flowers were held in deionized water but increased if held in 200 mg liter-1 8-HQC + 3% sucrose. The induction of ethylene biogenesis may be an injury response caused by sucrose.

Free access

Nicholas P. Howard, Dennis Stimart, Natalia de Leon, Michael J. Havey, and William Martin

Impatiens (Impatiens walleriana) are currently among the most valuable and widely cultivated floriculture crops in the world. Attractive floral display is a primary goal for breeders of impatiens. Although breeders have selected for this trait, little consideration has been given to floral longevity as a means to increase the floral display of bedding crops. In this study, 259 commercial inbred lines of impatiens were grown in a greenhouse and evaluated for floral longevity as defined by the time between when a flower was completely open to when all of the petals abscised from the pedicle. Mean floral longevity of inbreds ranged from 3.3 ± 0.4 to 15.8 ± 2.5 days. Twelve inbreds (six with long floral longevity and six with short floral longevity) were chosen and crossed in a half diallel to create 66 hybrids that were analyzed for floral longevity in three greenhouse environments. Mean floral longevity of hybrids across greenhouse environments ranged from 2.8 ± 0.4 to 14.1 ± 2.8 days. Significant general (GCA) and specific (SCA) combining abilities for floral longevity were detected. GCA mean squares were 37 times larger than SCA mean squares, revealing that additive genetic effects play a more important role in the inheritance of floral longevity in impatiens. This information, coupled with the significant amount of variation for floral longevity among inbreds, indicates that there is good potential for breeding for floral longevity in impatiens to improve the floral display of hybrids.