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Jodie L. Ramsay, Donald S. Galitz, and Chiwon W. Lee

Easter lily (Lilium longiflorum L.) cultivars Ace and Nellie White were regenerated through the culture of immature ovary tissues. Shoot initiation and proliferation were most efficient when a modified Murashige and Skoog (MS) medium containing 5% sucrose, 1 mg 2,4-D/liter, and 2 mg benzylamino purine (BAP)/liter was used. The shoots, when divided and subcultured on the same medium, formed roots within 4 weeks. The rooted plants were transferred to soil in a greenhouse. Root-tip smears made from the regenerated plants showed a range of variation in chromosome numbers from 10 to 25 per cell, in contrast to the bulb-grown plants, which had 2x = 24 chromosomes per cell. The mixoploid condition existed in many regenerants exhibiting chromosome number variation in different root cells of the same plant.

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H.M. Wallace, B.J. King, and L.S. Lee

Pollen source is known to affect the fruit size and quality of 'Imperial' mandarin, but no study has determined the appropriate orchard design to maximize the beneficial effects of pollen source. We determined the parentage of seeds of 'Imperial' mandarin using the isozyme shikimate dehydrogenase to characterize pollen flow and the effect on fruit size in an orchard setting. Two blocks were examined: 1) a block near an 'Ellendale' pollinizer block; and 2) an isolated pure block planting. Fruit size and seed number were maximum at one and three rows from the pollinizer (P ≤ 0.05). Isozyme results were consistent with all seeds being the result of fertilization by the 'Ellendale' pollinizer. In the pure block planting, fruits in rows 5-11 inside the block were very small with no seeds. This indicates poor pollen flow resulting in a reduction in fruit quality for the pure block. These results emphasize the importance of pollinizers in orchard design, and bees in orchard management. They suggest that each row should be planted no more than three rows from the pollinizer to maximize the benefits of the pollen parent in self-incompatible cultivars such as 'Imperial'.

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Jodie L. Ramsay, Donald S. Galitz, and Chiwon W. Lee

Influences of culture media, sucrose, and growth regulator concentrations on plant regeneration from Easter lily (Lilium longiflorum L.) were investigated. Ovary tissues excised from unopened flower buds (3-10 cm long) were cultured on either B-5 medium or MS medium containing 2, 5, or 10% sucrose, 0.8% agar or Phytagel, and varying concentrations of 2,4-D, kinetin, naphthaleneacetic acid (NAA) and benzyladenine (BA). Callus formation from explants was more prolific on MS medium than on B-5 medium and when cultures were initially placed in the dark for 20 days. Cultures grew best when the medium contained 5% sucrose. Shoot differentiation from callus was maximum when MS medium contained 1 mg/liter 2,4-D and 2 mg/liter BA. Roots developed when shoots were placed on the same medium with 1 mg/liter 2,4-D, 0.1 mg/liter NAA and 0.1 mg/liter kinetin. Rooted plants were successfully transferred into soil medium in a greenhouse.

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J.P. Syvertsen, J.W Grosser, and L.S. Lee

We grew three diploid (2X) Citrus rootstock seedlings and their autotetraploids (4X) at elevated CO2 to obtain insights into limitations on growth and net gas exchange that have been associated with tetraploidy. Well-nourished Volkamer lemon (Volk), Troyer citrange (Troy), and Cleopatra mandarin (Cleo) were grown in greenhouses at ambient or twice ambient CO2 for 3 months. We measured plant growth, water relations, mineral nutrition, and net gas exchange characteristics of leaves. Overall, tetraploid roots were thicker as 4X had lower root length: dry weight ratio or specific root length (SRL) than 2X roots. Tetraploid plants were smaller and had higher root/shoot ratios, shorter fibrous roots, and lower whole plant transpiration than 2X. Tetraploids also had lower leaf N and P concentrations on a dry weight basis. Since 4X leaves had thicker leaves (more dry weight per area) than 2X leaves, these nutrient differences disappeared when expressed on an leaf area basis. Elevated CO2 increased plant growth but decreased leaf N, P, and K apparently by a growth dilution effect. Elevated CO2 also increased fibrous root thickness, leaf thickness, and net assimilation of CO2 (ACO2) but decreased stomatal conductance and transpiration such that leaf water use efficiency increased. There was no effect of ploidy level on ACO2 but 4X Volk and Troy had lower rates of ACO2 than their diploids at elevated CO2. Hydraulic conductivity of intact root systems (measured in a pressure pot) was correlated to total plant growth but variability obscured effects of CO2 or ploidy on root conductivity. The low SRL of tetraploids were correlated with lower rates of water use and lower leaf nutrient concentrations, which may be operative in determining the growth characteristics associated with tetraploidy.

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Jodie L. Ramsay, Donald S. Galitz, and Chiwon W. Lee

Influences of culture media and sucrose concentrations on plant regeneration from Easter lily (Lilium longiflorum L. cv. Ace) ovary tissues were investigated. Pistils excised from unopened flower buds (3-5 cm long) were sectioned and cultured on either B-5 medium or Murashige and Skoog (MS) medium containing 2%, 5%, or 10% sucrose, with 1 mg·L-1 2,4-D and 2 mg·L-1 BA. Callus formation was most prolific on MS medium containing 5% sucrose. Shoot differentiation was higher on MS medium than on B-5 medium. Rooted plants were transferred into soil medium and grown in a greenhouse. Root tip smears showed that 35% of the regenerated plants showed a variation in chromosome numbers from 10 to 25 per cell, while the rest of the regenerants showed the normal 2n = 2x = 24 chromosomes per cell. The mixoploid condition also existed in different root cells of the same regenerated plant. Chemical names used: 2,4-dichlorophenoxyacetic acid (2,4-D); 6-benzylaminopurine (BA).

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J.P. Syvertsen, L.S. Lee, and J.W Grosser

Diploid (2x) and autotetraploid (4x) Citrus L. rootstock cultivars were grown at elevated CO2 to obtain insights into limitations on growth and net gas exchange that have been associated with tetraploidy. Well-nourished 2x and 4x seedlings of `Volkamer' lemon (Volk, C. volkameriana Ten & Pasq.), `Troyer' citrange [Troy, C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.] and `Cleopatra' mandarin (Cleo, C. reticulata Blanco.), were grown in greenhouses at either ambient or twice ambient CO2 for 4 months. Plant growth, water relations, mineral nutrition, and net gas exchange characteristics of leaves were measured. Most 4x plants were smaller and had lower rates of whole plant transpiration but shorter fibrous roots than 2x plants. Fibrous roots of 4x were thicker than 2x roots as indicated by a lower specific root length (SRL) in 4x than in 2x roots. Root hydraulic conductivity was correlated to total plant growth but there were no effects of CO2 or ploidy on root conductivity. Tetraploid leaves had lower N concentrations than 2x leaves when expressed on a dry weight basis but these differences disappeared when N concentration was expressed on an leaf area basis because 4x leaves had more leaf dry weight per area (LDW/a) than 2x leaves. Plant growth was greater and SRL was lower at elevated CO2 than at ambient CO2. LDW concentrations of N, P, and K were lower at elevated CO2 than at ambient apparently due to a growth dilution effect. LDW/a, net CO2 assimilation (ACO2), and leaf water use efficiency were greater at elevated CO2 than at ambient. Overall, there was no effect of ploidy on ACO2 but 4x Volk and Troy had lower rates of ACO2 than their 2x at elevated CO2. Net gas exchange of tetraploid leaves was less responsive to elevated CO2 than 2x leaves. The low SRL of tetraploids was correlated with low whole plant transpiration rates and low leaf area-based N concentrations, which may be operative in determining the growth characteristics associated with tetraploidy.