Producing high quality rooted stem cuttings on a large scale requires precise management of the rooting environment. This study was conducted to investigate the effect of the rooting environment on adventitious root formation of stem cuttings of loblolly pine (Pinus taeda L.). Hardwood stem cuttings of loblolly pine were collected in Feb. 2002 from hedged stock plants and stored at 4 °C until setting in Apr. 2002. One hundred stem cuttings per plot in each of two replications received 45, 61, 73, 102, 147, or 310 mL·m-2 of mist delivered intermittently by a traveling gantry (boom) system. Mist frequency was similar for all treatments and was related inversely to relative humidity (RH) within the polyethylene covered greenhouse. Rooting tubs in each plot were filled with a substrate of fine silica sand, and substrate water potential was held constant using soil tensiometers that activated a subirrigation system. Cutting water potential was measured destructively on two cuttings per plot beginning at 0500 hr every 3 hh until 2300 hr (seven measurements) 7, 14, 21, or 28 days after setting. During rooting, leaf temperature and RH were recorded in each plot to calculate vapor pressure deficit (VPD). Cutting water potential and VPD were strongly related to mist application. Cutting water potential was also related to VPD. Rooting percentage had a linear and quadratic relationship with mean cutting water potential and VPD averaged between 1000 and 1800 HR. Eighty percent rooting occurred within a range of values for VPD. Data suggest that VPD can be used to manage the water deficit of stem cuttings of loblolly pine to increase rooting percentage. These results may be applicable to other species and to other rooting environments.
Experiments conducted in January (hardwood cuttings) and June (softwood cuttings) 1998 compared rooting and root dry weight (DW) of stem cuttings of three full-sib families of loblolly pine (Pinus taeda L.) rooted in Jiffy forestry peat pellets and Ray Leach Super Cells. Ray Leach Super Cells (vol.= 162 cm3) served as the control and contained a medium of 2 peat: 3 perlite (v/v). Pellet sizes used were 25-65, 30-65, 36-65, 36-75, 42-65, 42-80, and 50-95 (dry diam.-expanded height in mm). Cuttings were taken from hedged stock plants and rooted for 12 weeks under mist in a humidity-controlled greenhouse. Following evaluation for rooting in the June experiment, ≈500 rooted cuttings in pellets and Ray Leach Super Cells were field-planted in eastern Georgia in December 1998 to study the effect of pellet size and cutting development on first-year field growth. Rooting percentages in January for hardwood cuttings rooted in pellet sizes 42-80 (36%) and 50-95 (57%) were less than the control (83%). Root DW for each pellet size was less than the control. Rooting percentage in June for softwood cuttings rooted in pellet size 36-65 (77%) was greater than the control (64%) whereas rooting percentages for cuttings rooted in pellet sizes 42-80 (50%) and 50-95 (52%) were less than the control. Root DWs for cuttings in pellet sizes 25-65, 30-65, 36-65, and 42-65 were less than the control. Field performance data will be presented.
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.
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).
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.
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.