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Ignacio Espinosa and Will Healy

One-year-old corms of Liatris spicata Willd. produced from seed and 2-year-old corms from division of previously forced corms were placed under 8 hours of natural daylight plus 0, 4, 6, or 8 hours of incandescent (5 μmol·s-l·m-2) day continuation to equal 8-, 12-, or 16-hour photoperiods. Plants were grown under these photoperiods during the first 35 days after shoot emergence (initial) and then were grown under a second photoperiod of 8, 12, 14, or 16 hours until harvest (final). The combination of initial and final photoperiod treatments resulted in a total of 16 photoperiod combinations. Two-year-old corms flowered 10 days earlier than l-year-old corms, but l-year-old corms produced twice as many vegetative shoots and 15% more flowering shoots than the 2-year-old corms. Long initial photoperiod (14 or 16 hours) treatments. (LD) reduced-the days to flower by 8 days and increased flower shoot elongation by 20 cm, compared with initial short days (8 or 12 hours, SD). However, initial LD treatments decreased the number of flowering shoots by 50%, compared to initial SD treatments. An initial SD followed by a final LD did not decrease the number of flowering shoots, yet promoted greater stem elongation (92 cm) than continuous LD (83 cm).

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Yin-Tung Wang

Leaf blades, axillary buds, shoot tips, green bark, suberized bark, or the whole plant of container-grown Hibiscus rosa-sinensis L. cv. Jane Cowl were treated with uniconazole. Applying uniconazole (50 mg·liter-1) to axillary buds or the green bark below a bud immediately after pruning limited elongation of the first three internodes. Length of the fourth internode was unaffected, regardless of the site of uniconazole application. When used on plants with 24-day-old shoots, uniconazole (40 mg·liter -1) applied to the whole plant provided the only satisfactory height control. Leaf size was reduced by nearly 50%, with a concomitant increase (12%) in fresh weight per unit area. GA3 (50 mg·liter-1, was more effective in promoting elongation of shoots previously retarded with a drench application of uniconazole (0.1 mg/2.6-liter pot) when applied to the whole shoot, leaf blades, or shoot tip. Application of GA, only to the stein surface, whether old or young, did not effectively encourage the growth of shoots of plants previously treated with uniconazole. Chemical names used: (E)-1-(p-chlorophenyl) -4,4-dimethyl-2-(1,2,4-triazole-1-yl)-1-penton-3-ol (uniconazole); analogue of (1α,2β,4 α,4bβ,10β)-2,4a,7-trihydroxy-1-methyl-8-methylenegibb-3-ene-1,10 dicarboxylic acid 1,4a-lactone (GA3).

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M. Tagliavini and N.E. Looney

Root and shoot growth of peach seedlings was strongly suppressed when the roots were held at 8 to 10C. Shoot and root dry weights and root volume increased linearly with increasing root-zone temperature (RZT) to 22C. GA3 at 5.7 μm (2 ppm) added to the aerated full nutrient solution reversed the effect of low RZT on shoot elongation but inhibited root growth at all RZTs. Paclobutrazol (PBZ) (6.8 × 10-3μm) (2 ppb) inhibited shoot elongation at all RZTs and shoot dry weight at 16 and 22C. However, PBZ had no effect on root dry weight accumulation at any RZT. The shoot growth-promoting effect of GA3, relative to control plants, disappeared at higher RZTs, but GA3 reversed the growth-inhibiting effect of PBZ at all RZTs. PBZ increased mean root diameter at all RZTs and significantly increased root volume at 22C. These results show that growth of peach seedlings is profoundly influenced by a cool root-zone environment. The plant growth regulator effects suggest that seedling roots play an important role in whole-plant gibberellin physiology. Some possible implications for fruit production are discussed. Chemical names used: gibberellic acid (GA3); β -[(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol(paclobutrazol,PBZ).

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Yin-Tung Wang, Kuo-Hsiun Hsiao, and Lori L. Gregg

Cuttings of Epipremnum aureum (Linden & André) Bunt. were soaked for 5 seconds in 5% Folicote or Stressguard antitranspirant solution, planted immediately or after 6 hours, and misted or not misted during the daylight hours for 2 weeks. Neither antitranspirant affected the growth of misted cuttings. However, in nonmisted cuttings, Folicote resulted in delayed first leaf unfolding and small plants. Misting improved shoot growth relative to not misting. In a second experiment, Stressguard sprayed on leaves of stock plants resulted in slow growth of cuttings taken from them, while Folicote had no effect. Water stress induced by delayed planting resulted in water loss and slow lateral shoot growth in both experiments. Application of uniconazole at the four-leaf stage at 0.05 to 0.4 mg/0.5-liter pot reduced stem elongation, leaf count, and the length of nodal roots. Uniconazole increased individual leaf size on the main shoot and promoted the growth of basal lateral shoots. While stem and total plant dry weights were reduced, total leaf dry weight was not affected by uniconazole. Uniconazole continued to provide good control on the elongation of newly emerged lateral shoots and promoted the production of more and larger leaves when evaluated 4 weeks after the main shoot was severed above the fourth basal node. Chemical name used: (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-trizol-1-yl)-1-penten-3-ol (uniconazole).

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Riccardo Lo Bianco, Mark Rieger, and She-Jean S. Sung

Terminal portions of `Flordaguard' peach roots [Prunus persica (L.) Batsch] were divided into six segments and the activities of NAD+-dependent sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX), sucrose synthase (SS), soluble acid invertase (AI), and soluble neutral invertase (NI) were measured in each segment 10, 15, and 20 days after seed germination. The same type of experiment was conducted with terminal portions of `Flordaguard' and `Nemaguard' peach shoots except that one of the six segments consisted of the leaflets surrounding the apex. Independent of the age of individual roots, activities of SDH and AI were consistently highest in the meristematic portion and decreased with tissue maturation. In shoots, AI was the most active enzyme in the elongating portion subtending the apex, whereas SDH was primarily associated with meristematic tissues. A positive correlation between SDH and AI activities was found in various developmental zones of roots (r = 0.96) and shoots (r = 0.90). Sorbitol and sucrose contents were low in roots regardless of distance from tip, while sucrose showed a decreasing trend with distance and sorbitol, fructose, and glucose increased with distance from the meristem in shoots. Activity of SDH in internodes, but not apices, correlated with shoot elongation rate of both cultivars, whereas activities of other enzymes did not correlate with shoot elongation rate. We conclude that AI and SDH are the predominant enzymes of carbohydrate catabolism and the best indicators of sink growth and development in vegetative sinks of peach.

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Michael E. Compton and D.J. Gray

Cotyledon explants of four watermelon [Citrullus lanatus (Thunb.) Mataum. & Nakai] breeding lines (F92U8, SP90-1, SP90-2, and SP90-4) were prepared from mature seed or from 2-, 4-, 6-, 8-, or 10-day-old seedlings. Explants were incubated on shoot regeneration medium for 8 weeks followed by 4 weeks on shoot elongation medium. The four genotypes differed in their ability to produce shoots at each explant age. The highest frequency with which F92U8 (66%) and SP90-2 (60%) explants produced shoots was for 2-day-old seedlings. Fewer explants formed shoots when established from mature seed or seedlings older than 2 days. In contrast, the percentage of SP90-4 explants that produced shoots was highest when cotyledons were obtained from 4-day-old seedlings (40%), but the response was less than the optimum for F92U8 and SP90-2. SP90-1 cotyledon explants exhibited the poorest response of the four breeding lines (<11% produced shoots), with little difference in response among the explant ages tested. The number of shoots per responding explant also depended on the age of the explant source. Explants from 2- to 4-day-old seedlings produced the most shoots. Fewer shoots formed on cotyledons from mature seed or seedlings older than 4 days.

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Sharon A. Bates, John E. Preece, and John H. Yopp

Dissected white ash seeds were placed on an agar-solidified MS medium with 10 μM TDZ and 1 μM 2,4-D (shoot initiation medium). After 4 weeks, explants were transferred to shoot elongation medium (3 μM TDZ, 1 μM BA, and 1 μM IBA) solidified with 0.7% Sigma agar, 0.525% agar + 0.05% gelrite, 0.35% agar + 0.1% gelrite, 0.175% agar + 0.15% gelrite, 0.2% gelrite, or no gelling agent (liquid medium). After 12 weeks in vitro, shoot growth and number were suppressed in cultures containing 0.2% gelrite (9.3 mm and 0.7 shoots) and in cultures containing no gelling agent (6.9 mm and 0.7 shoots). There were no differences in shoot growth and number in cultures containing 0.7% Sigma agar (2.2 mm and 16.5 shoots), 0.525% agar + 0.05% gelrite (2.6 mm and 18.7 shoots), 0.35% agar + 0.1% gelrite (1.6 mm and 17.4 shoots), and 0.175% agar + 0.15% gelrite (2.0 mm and 20.4 shoots). The most vitrification occurred in cultures on medium with the lowest amount of agar, gelrite only, and liquid medium.

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Lynne Edick Caton and Steve McCulloch

Briggs Nursery has micropropagated lilacs commercially since 1982. Presently we are producing more than 30 species and hybrids and have observed that media requirements vary significantly. In this study 5 lilacs representing a range of germtypic and phenotypic differences were examined to optimize cytokinin concentrations for shoot growth in vitro. Lilacs were grown on MS salts with BA, 2iP, and zeatin used individually and in combination. Plants were subculture 3 times, at 6 week intervals, at the conclusion of which quantitative data was taken with respect to shoot multiplication, elongation, and quality. These factors help determine the commercial practicality of producing lilacs through tissue culture.

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Wayne A. Mackay

Mature flowering Arbutus texana trees were successfully micropropagated from shoot tips. Optimum shoot proliferation was achieved on a basal medium consisting of WPM salts, MS vitamins, and sucrose supplemented with 11.1 or 22.2 μm BA and no auxin. Microcuttings rooted readily when pulsed with 6.1 μm IBA for 1 week and transferred to auxin-free medium. The addition of charcoal to the rooting medium improved root branching and elongation but suppressed root formation. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA); indole-3-butyric acid (IBA).

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Francine Bigras

Spring frosts frequently cause significant damage to conifer seedlings during bud flushing and shoot elongation in forestry nurseries. To ensure adequate protection, levels of frost sensitivity must be known during these stages of development. Eight-month-old, containerized, black spruce seedlings were submitted to freezing temperatures of 0, –4, –6, –8, and –10C for 1, 2, 3, 4, 5, and 6 h at the following stages: 1) nonswollen buds; 2) swollen buds; 3) bud scales bursting, needle tips emerging; and 4) shoot elongation, 1 to 5 cm. After the treatments, seedlings were grown for 90 days in a greenhouse. Seedling survival then was estimated; dead seedlings discarded; and damage to buds, needles, and roots and shoot increment and diameter were measured on the remaining seedlings. Results show that frost sensitivity increases with the developing bud and shoot. A decrease in seedling and bud survival was noted with an increase in time of exposure (stages 2, 3, 4); otherwise, time exposure has no effect. Damage to needles and roots increases and diameter decreases with decreasing temperatures at all stages. Shoot increment was influenced by decreasing temperatures at stages 2 and 3 only.