Stumping Height, Crown Position, and Age of Parent Tree Influence Rooting of Stem Cuttings of Fraser Fir

Abstract

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.