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James M. Garner and Allan M. Armitage

Limonium × `Misty Blue' plants were treated with directed sprays of gibberellic acid (GA3) at 400 mg·liter–1 at weekly intervals. All GA3 treatments accelerated flowering and increased yield of flowering stems compared to nontreated plants. Treatment at 4 weeks after planting resulted in the greatest acceleration of flowering and increase in stem yield.

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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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Kitren G. Weis, Stephen M. Southwick, and George C. Martin

Gibberellic acid reduces return bloom in many fruit tree species. Reducing bloom may cut costs of hand thinning apricot, peach and plum fruit. Sprays of 250 ppm GA, during floral bud evocation (June 1993) resulted in bud death and abscission as determined by light microscopy sections in `Patterson' apricot (Prunus armeniaca L). GA treatment in May did not cause observable effects. August treatments, immediately prior to floral initiation, did not impede differentiation. Treatment of `Elegant Lady' peach (Prunus persica [L.] Batsch.) buds with 75-250 ppm GA, in late June, 1993 (evocation phase) did not have any discernable effects in that season with respect to abscission or differentiation. Treated peach buds differentiated simultaneously with untreated buds in early August. The patterns of response to GA treatment imply `windows of opportunity' with respect to effectiveness of GA treatments. The specific response suggests that apricot buds possess differing levels of sensitivity to GA treatment and probably reflect distinct phases in transition to flowering. In August buds were already `determined' and were in a potentially floral state that was irreversible.

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John E. Erwin and Gerald Pierson

Lypcopersicum esculentum cv `Money Maker' seeds were germinated at constant 20C. Three days after germination seedlings were randomly divided into 3 groups and placed into 3 growth chambers maintained at 23/17, 20/20, or 17/23C (day/night temperature) (DT/NT). Irradiance and photoperiod were maintained at 250 μmol s-1 m-2 and 12 hrs, respectively. At the 2 leaf stage, plants in each chamber were divided into 3 groups of 3 plants each to receive a growth regulator treatment. Growth regulator treatments consisted of spray applications of either ancymidol (52ppm), GA3 (12ppm), or water applied every 3 days for 21 days. Measurements were taken on internode length and chlorophyll content after 21 days. Internode length increased as the difference (DIF) between DT and NT increased (DT-NT). Exogenous applications of GA3 overcame inhibition of stem elongation resulting from a -DIF environment. Application of ancymidol did not significantly decrease stem elongation in a -DIF environment. Temperature regime had a significant impact on chlorophyll content per mg dry weight. In contrast, growth regulator applications had a significant impact on chlorophyll content cm-2. There was no significant impact of either temperature regime or growth regulator treatment on the chlorophyll a/b ratio.

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Sonja L. Maki, Sriyani Rajapakse, Robert E. Ballard, and Nihal C. Rajapakse

Plants grown in far red (FR) light deficient environments are typically shorter because of short internodes, resembling plants treated with GA biosynthesis inhibitors. The role of GAs in the reduction of stem elongation of `Bright Golden Anne' chrysanthemum [Dendranthem ×grandiflora (Ramat.) Kitam. (syn. Chrysanthemum ×morifolium Ramat.)] grown in FR light deficient (-FR) environment was investigated by following the response of chrysanthemums grown in - FR environment to exogenous application of GA1, GA19, or GA20, and the metabolism of GA12 and GA19 in -FR or +FR environment. FR light deficient environment resulted in 25% to 30% shorter plants than in +FR environment. Final height of GA1- and GA20-treated plants followed a quadratic pattern while that of GA19 treated plants followed a linear pattern as the dosage increased from 0 to 50 μg/apex. The response to GA1 was the greatest followed by GA20 and GA19, regardless of the light environment. Application of GA1 (50 μg/apex) increased final height by 65% compared with no GA (0 μg/apex) application under either +FR or -FR light environment, suggesting the response to GA1, which is the active form, remained the same. Responses to GA19 and GA20 declined under -FR light. [14 C]GA12 and [14C]GA19 metabolized slowly in the -FR environment suggesting that the turnover of GAs may have caused in part the lower response to GA19. Although metabolism of GA1 under -FR environments was not investigated, observations with GA1 application experiments support that -FR environment may have enhanced inactivation of GA1. Chemical name used: gibberellic acid (GA).

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Wallace G. Pill and Elizabeth A. Kilian

`Moss Curled' seeds of parsley (Petroselinum crispum L.) were primed osmotically in polyethylene glycol or matrically in fine, exfoliated vermiculite at -0.5 MPa for 4 or 7 days at 20 or 30 °C with 0 or 1 mm GA3. All priming treatments stimulated and hastened germination. Matric priming resulted in greater germination (89%) than osmotic priming (83%) when seeds were primed for 7 days at 30 °C, but priming agent had no effect on germination percentage following priming at 20 °C or for 4 days. In seeds primed for 4 days at 20 or 30 °C, matric priming hastened germination more than did osmotic priming. Germination was generally less synchronous with matric than with osmotic priming. Increasing priming time from 4 to 7 days increased the rate of germination, but increased germination synchrony only when seeds were primed a t 20 °C. Inclusion of 1 mm GA3 during priming had little or no effect on germination. All matric priming treatments (other than 4-day priming) were repeated to assess seedling emergence in a greenhouse (25°C day/22 °C night). Priming increased the percentage, rate and synchrony of emergence, and increased hypocotyl length at 3 weeks after planting. Priming at 30 °C with 1 mm GA3 resulted in the greatest emergence percentage, hypocotyl length, and shoot dry weight. We conclude that matric priming is a satisfactory alternative to osmotic priming of parsley seeds. Chemical name used: gibberellic acid (GA3).

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Wallace G. Pill and Elizabeth A. Kilian

`Moss Curled' seeds of parsley (Petroselinum crispum L.) were primed osmotically in polyethylene glycol or matrically in fine, exfoliated vermiculite at –0.5 MPa for 4 or 7 days at 20 or 30 °C with 0 or 1 mm GA3. All priming treatments stimulated and hastened germination. Matric priming resulted in greater germination (89%) than osmotic priming (83%) when seeds were primed for 7 days at 30 °C, but priming agent had no effect on germination percentage following priming at 20 °C or for 4 days. In seeds primed for 4 days at 20 or 30 °C, matric priming hastened germination more than did osmotic priming. Germination was generally less synchronous with matric than with osmotic priming. Increasing priming time from 4 to 7 days increased the rate of germination, but increased germination synchrony only when seeds were primed at 20 °C. Inclusion of 1 mm GA3 during priming had little or no effect on germination. All matric priming treatments (other than 4-day priming) were repeated to assess seedling emergence in a greenhouse (25°C day/22 °C night). Priming increased the percentage, rate and synchrony of emergence, and increased hypocotyl length at 3 weeks after planting. Priming at 30 °C with 1 mm GA3 resulted in the greatest emergence percentage, hypocotyl length, and shoot dry weight. We conclude that matric priming is a satisfactory alternative to osmotic priming of parsley seeds. Chemical name used: gibberellic acid (GA3).

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Moo R. Huh, Beyoung H. Kwack, and Leonard P. Perry

Salt injury was induced by 5% (w/v) NaCl drenching on Hibiscus hamabo Sieb. & Zucc. and H. syriacus L. seedlings. Total chlorophyll content of H. hamabo was higher than that of H. syriacus. Uniconazole (0.0, 0.5, 1.0, and 5.0 mg·liter–1) treatment increased and 25- or 50-mg·liter–1 GA3 treatment decreased chlorophyll content of H. hamabo. Total chlorophyll content of H. syriacus was not affected by uniconazole or GA3. Total carbohydrate content of H. syriacus was more accumulated than that of H. homabo. Total carbohydrate content of H. hamabo was more decreased than that of H. syriacus by Ca (13.35 or 133.5 mM), uniconazole, or GA3 in relation to total carbohydrate contents. Protein contents of H. hamabo were higher than those of H. syriacus. Uniconazole or GA3 increased those of H. hamabo and decreased those of H. syriacus. Peroxidase activity of H. hamabo was higher than that of H. syriacus. Uniconazole decreased that of H. hamabo and increased that of H. syriacus. GA3 or Ca (13.35 mM) treatment increased that of both species. ATPase activity of H. hamabo was higher than that of H. syriacus. Uniconazole (5 mg·liter–1), GA3, or Ca decreased that of H. hamabo increased that of H. syriacus.

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Moo R. Huh, Beyoung H. Kwack, and Leonard P. Perry

Shoot length, leaf length and width, root length, and crown diameter were affected by 0.0-, 0.5-, 1.0-, and 5.0-mg·liter–1 uniconazole drench and 25- or 50-mg·liter–1 GA3 spray but not significantly by 0.0%, 2.5%, and 5.0% NaCl. Leaf width of H. syriacus Sieb. & Zucc. was not affected and that of H. syriacus L. significantly decreased, as NaCl concentration increased. Effect of NaCl on H. syriacus leaf width was offset by treatment with uniconazole but not by GA3 treatment. With 2.5% NaCl, dry weight of H. hamabo treated with uniconazole or GA3 increased and that of treated H. syriacus decreased. With 5.0% NaCl, dry weight of both species decreased with uniconazole or GA3. Calcium at 13.35 or 133.5 mM decreased the reduction of dry weight by NaCl treatment. The dry: fresh weight ratio of H. hamabo and H. syriacus treated with NaCl plus uniconazole was higher than that only treated with NaCl. GA3 treatment with NaCl did not affect the dry: fresh weight ratio for either species