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  • Author or Editor: Farrell C. Wise x
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Forest products companies would like to grow clonal plantations of superior loblolly pine (Pinus taeda L.) to improve fiber yields. Feasibility depends on developing efficient propagation techniques and finding superior clones. Horticultural stem-cutting propagation methods and micropropagation techniques are being coupled to test, preserve, multiply, and ultimately deploy clones. Outstanding clones are being found through a series of field tests; each beginning with a superior full-sibling cross from a 40-year-old breeding program. Clones are first screened for rooting ability, and the top 25% to 35% of clones are then established on four sites. Since maintenance of juvenile phase tissue is critical to perpetuating high rooting rates and fast subsequent growth, each clone is preserved as a set of serially propagated hedges and as cold-stored microshoots. As field tests age, better-performing clones are multiplied gradually. Large-production stock blocks of juvenile hedges consequently may be established from both rooted cuttings and microshoots as soon as field tests end. Clones producing large numbers of long branches have been noted for their potential value as fast-growing ornamentals. Since such characters are opposite those desirable for forestry, these clones would need to be preserved, multiplied, and marketed separately from clones for plantation forests.

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Seeds of `Dawn Carpet' and `Little Bright Eye' annual vinca [Catharanthus roseus (L.) G. Don] were subjected to 32 treatments, arranged as a four × four × two factorial. For each cultivar, seeds were exposed to one of four temperatures (15, 20, 25, or 30C) during the 8-hour (day) and 16-hour (night) portions of the cycle. Within each temperature regime, half the seeds of each cultivar were irradiated for 1 hour daily, and the other half remained in constant darkness. Final germination percentages were suppressed at 15C day or night temperatures; at temperatures ≥20C, there were no significant differences between treatments. Heat input (daily degree hours) was a controlling factor in germination; different temperature cycles with equivalent numbers of daily degree hours had similar effects on germination response. There was a strong interaction between temperature and irradiation regime for both cultivars. Irradiating seeds for 1 hour/day reduced final germination percentages under cool (15C) conditions; response was not adversely affected when seeds at 15C were germinated in darkness. In a second experiment, seeds at 25C were exposed to daily photoperiods of 0, 1, 2, 4, 8, 12, or 24 hours. Germination percentages obtained in darkness and at photoperiods ≤12 hours were equivalent. Twenty-four-hour photoperiods suppressed germination compared to all other irradiation treatments.

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Abstract

Dormant hardwood stem cuttings of Fraser Fir [Abies fraseri (Pursh) Poir.] were severed from upper and lower tree crowns and artificially chilled at 4°C for 0, 4, or 8 weeks to achieve a partial break in rest. Following chilling, the resulting semi-dormant cuttings were treated with 0, 1500, 3000, or 4500 ppm IBA, and rooted for 135 days using a heated medium in a cool greenhouse. Rooted cuttings were evaluated, potted, and rechilled for 11, 7, or 3 weeks so that all cuttings were chilled a total of 11 weeks. Vegetative growth then was evaluated after a 12-week growing period. Cuttings initially chilled 4 weeks rooted in highest percentages, regardless of crown position, and exhibited little or no bud activity. Subsequent expansion of terminal and subterminal buds was greatest for cuttings initially chilled 0 or 4 weeks. Superior overall responses were achieved with upper-crown cuttings chilled 4 weeks and then treated with 4500 ppm IBA, or lower-crown cuttings dipped in 3000 ppm IBA after 4 weeks of chilling. The separation of rooting and budbreak apparently produced rooted cuttings comparable in size to 2-year-old plants grown from traditional hardwood cuttings. Chemical name used: 1H-indole-3-butanoic acid (IBA).

Open Access

Clonal propagation of recalcitrant conifers like loblolly pine depends on producing juvenile cuttings on hedges sheared several times annually. Although dormant cuttings root well, it will be economically important to also root softwood shoots produced between shearings. Several variables were therefore evaluated in a factorial experiment to enhance rooting and handling of summer cuttings. Rooting percentages were equivalent for 3 media after a 5-week hardening period (56% overall), but open flats of 1 perlite:1 vermiculite induced larger root systems at the end of rooting and hardening phases. Extending the rooting period from 10 to 14 weeks increased rooting from about 45% to 58% by the end of hardening. Primary root length per cutting increased 12-63% during hardening, depending on medium. After transplanting, overwintering survival was 98%. Foam rooting wedges produced smallest root systems, and resulting plants were consistently shortest through the following growing season. Weekly applications of soluble fertilizer during the last 6 weeks of rooting did not improve rooting or subsequent growth

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Abstract

Timing of severance, auxin treatment, and staking were evaluated for their effects on reducing abaxial-concave bending of softwood Fraser fir [Abies fraseri (Pursh) Poir.] stem cuttings. Cuttings collected 21 July 1983, were much less plagiotropic after a 135-day rooting period than those collected 3 weeks earlier. This upright habit was related to stronger internal support from increased amounts of xylem and lignified pith at severance. Staking also reduced abaxial-concave bending, but postseverance auxin treatment had no effect. Stakes apparently provided external support until stems became lignified. Nonstaked cuttings collected 30 June 1983 continued to exhibit greatest bending at the end of the 2nd growing season. Basal defoliation and wounding in preparation for rooting increased plagiotropic growth and reduced survival during rooting, but did not affect the percentage of rooting. Evaluation of xylem distribution indicated that abaxial-concave bending in the 2nd season was caused by greater production of compression wood and total xylem on adaxial than on abaxial sides of the original cutting segments.

Open Access

Two experiments were conducted during which juvenile hardwood or softwood stem cuttings of loblolly pine (Pinus taeda L.) were rooted under six mist regimes in a polyethylene-covered greenhouse to investigate the effect of mist level on vapor pressure deficit (VPD) and cutting water potential (Ψcut), and to determine the relationships between these variables and rooting percentage. In addition, net photosynthesis at ambient conditions (Aambient) and stomatal conductance (gs) were measured in stem cuttings during adventitious root formation to determine their relationship to rooting percentage. Hardwood stem cuttings rooted ≥80% when mean daily VPD between 1000 and 1800 hr ranged from 0.60 to 0.85 kPa. Although rooting percentage was related to Ψcut, and Aambient was related to Ψcut, rooting percentage of softwood stem cuttings was not related to Aambient of stem cuttings. Using VPD as a control mechanism for mist application during adventitious rooting of stem cuttings of loblolly pine might increase rooting percentages across a variety of rooting environments.

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Two experiments were conducted to develop a protocol for rooting stem cuttings from 3-, 5-, and 7-year-old fraser fir [Abies fraseri (Pursh) Poir.] Christmas trees. The first experiment tested the effect of stumping treatments and tree age on shoot production and subsequent adventitious rooting. One auxin concentration [4 mm indole-3-butyric acid (IBA)] and a nonauxin control were tested. Stock plants were stumped to the first whorl (trees in the field 3 and 5 years) or the first, third, and fifth whorls (trees in the field 7 years). Intact (nonstumped) controls were also included for each age. The second experiment was designed to create a quantitative description of the effects that crown (foliage and above ground branches of a tree) position have on the rooting of stem cuttings collected from stumped and nonstumped trees. The exact position was determined by measuring the distance from the stem, height from the ground, and the degrees from north. Crown positions were recorded as cuttings were collected and then cuttings were tested for rooting response. The rooting traits assessed in both experiments included rooting percentage, percent mortality, number of primary roots, total root length, root symmetry, and root angle. In the first experiment, rooting percentage, primary root production, and total root length increased as the age of the stock plant decreased and the severity of the stumping treatment increased. Auxin treatment significantly increased rooting percentage, root production, root lengths, and root symmetry while decreasing mortality. Overall, the highest rooting percentages (51%) and the greatest number of primary roots (8.1) occurred when 3-year-old stock plants were stumped to the first whorl and treated the cuttings with 4 mm IBA. The greatest total root lengths (335 mm) occurred in cuttings from the 3-year-old stock plants. In the second experiment, rooting percentage was significantly affected by the position from which the cuttings were collected. Cuttings collected lower in the crown and closer to the main stem rooted more frequently than cuttings collected from the outer and upper crown.

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Seven concentrations of indole-3-butyric acid (IBA), seven concentrations of 1-naphthaleneacetic acid (NAA), and a nonauxin control were tested over three growth stages to determine their ability to promote adventitious rooting of stem cuttings from 3- and 4-year-old stock plants of virginia pine (Pinus virginiana Mill.). Cuttings were harvested September 2000 (semi-hardwood), February 2001 (hardwood), June 2001 (softwood), and October 2001 (semi-hardwood), treated with auxin concentrations ranging from 0 to 64 mm and placed under intermittent mist in a greenhouse. Rooting percentage, percent mortality, number of primary roots, total root length, root symmetry, root angle, and root diameter were assessed following 16 weeks. Growth stage affected every rooting trait measured except root symmetry and diameter. Auxin type affected total root length and root diameter, while auxin concentration affected every rooting trait except root angle. The highest predicted rooting percentages (46%) occurred when semi-hardwood cuttings were collected in September 2000 and treated with 7 mm auxin. Cuttings collected within the same growing season (2001) exhibited the highest predicted rooting percentage (33%) when softwood cuttings were treated with 6 mm auxin. Semi-hardwood cuttings rooted in 2001 produced the greatest number of roots and root lengths. Root diameter was significantly greater when NAA rather than IBA was applied, especially at higher concentrations.

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Seven concentrations of IBA and seven concentrations of NAA plus a nonauxin control were tested over three growth stages to determine their effectiveness in promoting adventitious root formation on stem cuttings taken from 3- and 4-year-old stock plants of Fraser fir [Abies fraseri (Pursh) Poir.]. Cuttings were prepared in March (hardwood), June (softwood), or November (semi-hardwood) 2001, treated with auxin concentrations ranging from 0 to 64 mm, and placed under mist. Rooting percentage, percent mortality, number of primary roots, total root length, root system symmetry, and root angle were recorded after 16 weeks. Growth stage and auxin concentration significantly affected every rooting trait except root angle. NAA significantly increased the number of primary roots and total root length. However, auxin type did not significantly affect rooting percentage or percent mortality. The highest rooting percentages (99%) occurred when softwood cuttings were treated with 5 mm auxin, however, semi-hardwood cuttings also rooted at high percentages (90%) and had no mortality when treated with 14 mm auxin. Regardless of auxin type, the number of primary roots and total root length varied in similar patterns across concentration, although, NAA tended to induce a greater response. To root Fraser fir stem cuttings collected from 3- and 4-year-old stock plants, it is recommended that a concentration of 5 mm NAA should be used on softwood cuttings and 14 mm IBA on semi-hardwood cuttings. Chemical names used: indole-3-butyric acid (IBA); 1-naphthaleneacetic acid (NAA).

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