CIRCULAR 186 APRIL ARL17 1971 Cutting Orientation and Root Development of Cottonwood Agricultural A U BU RN EV. Smith, Director Experiment Station Auburn, Alabama U NI V ER S ITY CONTENTS Page METHODS 8 RESULTS AND DISCUSSION 4 S UM M A R Y ---------- ------------------------------- - 8 LITERATURE CITED 9 FIRST PRINTING 3M, APRIL 1971 Cutting Orientation and Root Development of Cottonwood JOHN C. BROWN and MASON C. CARTER' USE OF UNROOTED CUTTINGS of COttonwood (Populus deltoides Bartr.) for plantation establishment is a common practice and it has been recommended that cuttings be oriented in an upright position (4). However, in large scale commercial plantings, much effort is involved in handling and arranging the cuttings to prevent inversion. Shapiro (6) reported that cuttings of Populus nigra var. italica collected during the dormant season did not exhibit a polar distribution of roots. Instead they initiated roots along their entire length. The authors have observed cuttings, inadvertently inverted during planting, that initiated shoot growth and survived for several weeks. Occasionally inverted cuttings have been found to make near normal height growth. These observations suggest that at least some clones of cottonwood are capable of reversing their polarity and that the effort made to plant cuttings in an upright position is unnecessary. The present investigation was conducted to determine the extent to which orientation influences root development on cottonwood cuttings and the effect of auxin treatment on this process. THE METHODS One-year-old cottonwood sprouts growing in the Auburn Forest Nursery provided the source of the cuttings used. Original collections of cuttings were made along the Alabama River in Clarke County, Alabama. Fifteen cuttings, 0.25-0.5 inches in diameter and 6 inches long, were collected from each of 10 clones. Cuttings were collected from the nursery in January. Former Research Assistant and Associate Professor of Forestry. Five treatments with 10 replications in a completely randomized design were used. For each treatment, three cuttings were selected from each clone, randomly mixed, and treated. Following treatment, cuttings were planted in 6-inch plastic pots containing a (1:1)sand-vermiculite mixture. Three cuttings were planted per pot and were then placed under intermittent mist spray in the greenhouse. Natural daylight was supplemented with 300 W incandescent lights to give a photoperiod of 16 hours. The treatments were as follows: Ck (check) - basal end of cutting soaked 4 hours in distilled water and planted upright. In (inverted) - apical end of cutting soaked 24 hours in distilled water and planted apical end down. SI (soaked and inverted) - basal end of cutting soaked 24 hours in 25 p.pm. :indole-3-acetic acid (IAA) and planted apical end down. SU (soaked and upright) - basal end of cutting soaked for 24 hours in 25 p.p.m: IAA and planted basal end down. IS (inverted and soaked) - apical end of cutting soaked 24 hours in 25 p.p.m. IAA and planted apical end down. Cuttings were potted in late January. After 41 days the plants from five replications of each treatment were removed from the pots and washed free of rooting medium so that measurements could be made. The remaining potted plants were removed from the mist bed and maintained in the greenhouse for an additional 6 months. RESULTS AND DISCUSSION All cuttings had survived and initiated shoot growth after 41 days, hence, inversion did not affect early survival. However, the number of roots produced per cutting was much lower on inverted cuttings than on those planted upright, Table 1, Figure 1. Shoot growth was also reduced by inversion, Table 1. This agrees with the findings of Allen and McComb (1) for cuttings collected in late winter. The shortage and sometimes complete absence of root development on inverted cuttings indicated that survival would have been much lower had these studies been conducted in the field rather than under mist-bed conditions. When the remaining potted cuttings were transferred from the mist bed to the greenhouse bench, mortality began to occur among the inverted cut[4] FIG. 1. Representative cuttings 41 days after planting; AC-soaked and upright; D-inverted and soaked. -check; B3-inverted; M\usi