Factors affecting the rooting of Fraser fir (Abies fraseri) and Virginia pine (Pinus virginiana) stem cuttings.

Abstract

The current research sought to determine the best methodologies to clone, through rooted cuttings, desirable genotypes of both Fraser fir and Virginia pine. Genetic improvement and subsequent production of genetically superior clones would provide Christmas tree growers with higher quality stock material capable of greatly increasing their profitability. Once desirable genotypes have been selected, propagation through the rooting of stem cuttings may provide an important means of not only preserving and maintaining, but also commercially propagating these genotypes.

The objectives of the first studies were to determine the optimal season, auxin type [IBA (indole-3-butyric acid) or NAA (1-naphthaleneacetic acid)] and auxin concentrations for promoting root initiation and subsequent root development in both species. Seven auxin concentrations (1-64 mM) of each auxin type, four combinations of both auxin types and a nonauxin control were applied to hardwood, semi-hardwood and softwood cuttings collected from three- or four-year-old Fraser firs and Virginia pines.

In three- and four-year-old Fraser firs, the effects of season and concentration were significant for numerous rooting traits, including rooting percentage, percent mortality, primary root production and total root lengths. The type of auxin, IBA or NAA, significantly affected the number of primary roots and total root length, but it did not significantly affect rooting percentage and percent mortality. The highest rooting frequencies and lowest rates of mortality occurred when cuttings were set in June or November and treated with 4 or 16 mM auxin, respectively. Regardless of auxin type, number of primary roots and total root length varied in similar patterns across concentration; however, NAA tended to produce greater responses. Combinations of IBA and NAA did not increase rooting traits above what was achieved with a single auxin type.

In the Virginia pine study, using three- and four-year-old stock plants, there were four setting periods: September 2000, February 2001, June 2001 and October 2001. Season significantly affected numerous rooting traits including rooting percentage, percent mortality, primary root production and total root lengths. Auxin type, IBA or NAA, significantly affected total root lengths, but did not significantly affect any other trait. The highest rooting frequencies and lowest rates of mortality occurred when cuttings were set in September or June and treated with a three second dip of 8 or 16 mM auxin, respectively. Combinations of IBA and NAA did not increase rooting above what was achieved with a single auxin type

Additional, research was focused on the production and rooting of vertically oriented (non-plagiotropic) shoots from older trees of these two species. Fraser fir Christmas trees were hedged to 1 whorl (trees in the field 3 and 5 years) or 1, 3, and 5 whorls (trees in the field 7 years). Three-year-old Virginia pines were stumped to ¼, ½ and ¾ their original height. Non-cut controls of both species were also included. A second experiment was designed to create a quantitative description of the effects that crown position had on the rooting of stem cuttings collected from stumped and control trees of both species. During the summer of 2001, cuttings from both species were collected and rooted to help understand how to optimize the production and rooting of cuttings by managing the 1) stumping height, 2) crown position, 3) age of the parent tree, and 4) auxin treatments.

Stumping height and age significantly increased rooting percentage, primary root production and total root lengths in three-, five-, and seven-year-old Fraser fir Christmas trees. These rooting traits increased as the severity of the stumping treatment increased and as the age of the stock plant decreased. Auxin concentration significantly affected nearly every rooting trait assessed. Rooting percentage was significantly affected by the position from which the cuttings were collected. Overall, the higher rooting percentages (51%) and greatest number of primary roots (8.1) three-year-old stock plants were stumped to the first whorl.

In four-year-old Virginia pine Christmas trees, stumping height significantly affected rooting percentage and percent mortality. Rooting percentage increased and percent mortality decreased as the severity of the stumping treatment increased. Auxin type significantly affected rooting percentage, percent mortality, primary root production and total root lengths. In general, NAA treated cuttings rooted in higher frequencies (74%), produced a greater number of primary roots (5.5), and longer total root lengths (601 mm) than did IBA treated cuttings. Combinations of IBA and NAA did not increase rooting traits above what was achieved with a single auxin type. Rooting percentage was significantly affected by the positions from which the cutting was collected. The length of the primary needle, significantly affected by stumping height, increased as the severity of the stumping treatment increased, and was positively correlated with rooting ability.