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Susan S. Han

Postproduction leaf yellowing of Easter lily (Lilium longiflorum Thunb.) can be prevented by using growth regulators. Solutions containing benzyladenine (BA) reduced the percentage of yellow leaves in cold-stored plants, but solutions containing gibberellic acid (GA3) were not effective. Treatment with commercial products containing GA4+7 (Provide) or GA4+7 and BA (Promalin) nearly completely prevented the development of leaf yellowing. Concentrations as low as 25 mg·L-1 were effective. Leaf yellowing was prevented by growth regulators only on leaves that had been treated, indicating that the growth regulators were not mobilized in the plants. Growth regulator solutions halted further development of leaf yellowing when applied to plants that already had some chlorotic basal leaves. This result suggests that growth regulators need not be applied preventively. Treatment can be delayed until chlorotic lower leaves are first seen on plants. The striking effects of growth regulators in preventing leaf yellowing did not affect the development and opening of flower buds.

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Susan S. Han

Leaf yellowing of excised Easter lily leaves was significantly delayed by application of gibberellic acids ≥250 mg·liter-1 or benzyladenine ≥50 mg·liter-1. Rapid development of foliar chlorosis following cold storage was delayed significantly by applying 500 mg·liter-1 of GA3 or BA before storage. Poststorage treatments were less effective. Development of chlorosis was associated with rapid loss of fresh weight and was not related to the aperture of the stomates (diffusive resistance). Respiration rates of leaves treated with growth regulators were significantly lower than those of the controls.'

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Susan S. Han and Jennifer Nobel

The study was conducted to determine if ethylene or ethephon, an ethylene-releasing compound, can be used to induce abscission of phylloclades of four cultivars of Easter cactus [Rhipsalidopsis gaertneri (Regel) Moran] to increase efficiency in vegetative propagation. Abscission occurred within 24 hours after commencement of the ethylene treatments. Phytotoxicity, as exhibited by water soaking, transparency, and darkening of the phylloclades, as well as percent abscission, increased with increasing concentrations of ethephon (0 to 10,000 μl·liter–1). Ethylene released from ethephon, not the acidity of the solution, was determined to be the cause of the phytotoxicity. In three out of the four cultivars, vegetative and root growth from propagated phylloclades was significantly restricted by treatments with ethephon. In comparison, vegetative growth from phylloclades treated with ethylene at 20 μl·liter–1 was the same as from those treated with air. Root growth of the ethylene-treated phylloclades was not studied. The acidity of the ethephon solutions likely affected the growing regions, resulting in a reduction in growth. The study shows that treatment with ethylene gas or the use of pH-adjusted ethephon solutions may be an alternative to the labor-intensive procedures associated with vegetative propagation of Easter cactus. Chemical name used: 2-chloroethylphosphonic acid (ethephon).

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Susan S. Han and Jennifer Nobel

Whitefly infestation of poinsettias arises frequently from cuttings that were infested at the start of the season. Experiments were conducted to investigate the feasibility of using short-term elevated CO2 to eliminate whiteflies on cuttings prior to planting. Results indicated that adult greenhouse whiteflies (Trialeurodes vaporarium) are highly susceptible to an elevated level of CO2. All adult whiteflies are killed after exposure to 25% or 50% CO2 for less than 10 hours. Eggs, however, are more resistant than adults where 80% survived 10-hr of 50% CO2 treatment. Tests on poinsettia cuttings demonstrated that prolonged exposure to elevated CO2 resulted in the development of toxic symptoms soon after the treatments. Tolerance of 'Lilo' exceeded that of 'Supjibi', revealing differences in susceptibility of the two cultivars to the elevated CO2 treatment. Believing that the reduction in O2, rather than the elevation of CO2, was the main cause of mortality, we are currently testing the effects of hypoxia on survival of whiteflies.

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Susan S. Han and Jennifer Konieczny

Eggs, larvae, pupae, and adult stages of greenhouse whitefly (Trialeurodes vaporarium Westwood) and silverleaf whitefly (Bemisia argentifolii Bellows & Perring) were exposed to insecticidal controlled atmospheres at 20 °C or 30 °C. Mortality data were calculated for each stage and results demonstrated that reduced-O2 atmospheres (an O2 level of <2 μL·L-1 balance in N2) resulted in faster and higher mortality than elevated-CO2 atmospheres (25% or 50% CO2). Responses, from the least to most tolerant stage was adult < larvae < eggs = pupae, regardless of the species of whitefly and treatment temperature. At 20 °C, treatment time required to kill >90% of adults, larvae, and eggs and pupae was 2, 4, and 8 hours, respectively. Increasing the treatment temperature from 20 to 30 °C reduced the treatment time to one-half that of 20 °C. Treatment time required to achieve complete elimination of the insects also caused phytotoxicity symptoms on poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch), thus, limiting use of insecticidal controlled atmospheres as the sole means for managing whitefly.

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Rosanne E. Franco and Susan S. Han

Senescence of lower leaves of Easter lilies (Lilium longiflorum Thunb.) was previously shown to be delayed with application of the growth regulators, gibberellic acid (GA3) and benzyladenine (BA). This study was done to determine the physiological effects of GA3 and BA in relation to the delay of leaf senescence. Foliar application with 500 ppm BA or GA3 delayed chlorosis and lowered respiration rate in Easter lily leaves. A combination of 500 ppm BA and 500 ppm GA3 was more effective than the individual application of each. Gibberellic acid, BA, or their combination before cold storage resulted in delayed chlorosis and lowered respiration following removal from cold storage. Treatment with growth regulators after cold storage was less effective. Senescence of leaves was not associated with ethylene since ethylene production by leaves was undetectable by gas chromatograph. In addition, pulsing or continuous treatment with silver thiosulphate (STS), an inhibitor of ethylene synthesis, did not delay foliar chlorosis. Analysis of carbohydrate levels in Easter lily leaves treated with GA3, BA, or their combination may contribute to the understanding of the physiological effects of these two growth regulators.

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Rosanne E. Franco and Susan S. Han

Senescence of excised Easter lily leaves is typically marked by a rise in respiration without a concomitant production of ethylene. Treating excised leaves with 500 mg·L-1 of gibberellic acid (GA3) or benzyladenine (BA) significantly delayed the onset of leaf yellowing, lowered the respiration rates by one-third to one-half, and markedly delayed the respiratory rise. Similar effects on respiration were detected in leaves treated with BA or GA3 before a 4-week period of cold storage and in leaves treated after chlorosis had initiated. Results of this study indicate that excised Easter lily leaves respond to the growth regulators with a significant decrease in respiration rate.

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Susan S. Han and Thomas H. Boyle

Experiments were performed to determine the effects of ethylene (C2H4) on the postproduction quality of Easter cactus [Hatiora gaertneri (Reg.) Barthlott and H. ×graeseri (Werderm.) Barthlott]. Significant differences in percent bud abscission were observed among cultivars when plants were exposed to 0.4 or 1.0 μL·L-1 C2H4 for 48 hours. Fewer buds abscised on `Andre' and `Red Pride' than on `Evita', `Rood', and `Thor-Anne'. Stage of floral development at the time of C2H4 exposure affected the pattern and severity of bud abscission for `Crimson Giant'. Percent bud abscission was greater for plants treated with 0.5 μL·L-1 C2H4 in the small-bud stage (largest buds 7 to 13 days from anthesis) than for plants treated in the medium-bud stage (largest buds 3 to 4 days from anthesis) or large-bud stage (largest buds 1 day from anthesis). Application of 1 or 2 mm silver thiosulfate (STS) was as effective as 3 mm STS in reducing bud abscission on plants exposed to 0.5 μL·L-1 C2H4 in the small-bud stage. Treatment with 2 mm STS before C2H4 exposure increased the display life (number of days from anthesis of the first flower to senescence of the last flower) of `Andre' in all three developmental stages, but increased the display life of `Crimson Giant' only in the small bud stage. These results demonstrate that the response of Easter cactus to C2H4 is affected by cultivar, C2H4 concentration, stage of floral development at the time of C2H4 exposure, and STS pretreatment.

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Susan S. Han, Abraham H. Halevy, and Michael S. Reid

Vase life of individual flowers of cut brodiaea (Triteleia laxa Benth.) inflorescences ended 4 days after opening. Best vase life was achieved by harvesting inflorescences 1 to 2 days before anthesis of the first flower and holding them in a vase solution containing 2% sucrose and 200 ppm 8-hydroxyquinoline citrate (HQC). Such inflorescences had a display life of 12 days. Decreasing the pH of the vase solution or pulsing inflorescences with 10% sucrose for 16 hours did not increase their longevity. T. laxa flowers pretreated with 10% sucrose overnight could be stored for up to 2 weeks without significant reduction in vase life.

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Susan S. Han, Abraham H. Halevy, and Michael S. Reid

Unpollinated brodiaea (Triteleia laxa Benth.; syn. Brodiaea laxa) flowers produced no measurable C2 H4 during their entire lives. Treatment with C2 H4 (0.03 μl·liter -1) induced senescence of open flowers, completely inhibited opening of buds and petal growth, and promoted ovary growth. Silver thiosulfate had no effect on flowers kept in air but counteracted the effects of applied C, H.. The effect of C2 H4 on ovary growth seems to be indirect, via promotion of petal senescence and mobilization of the petal's metabolites to the ovary. Brodiaea flowers are protandrous; the stigma appears to be receptive (as judged by a pollination-induced burst of ethylene synthesis) only when the petals start to senesce. At this stage, papillae on the stigma surface elongated and separated.