Nursery Rooting and Growth of Loblolly Pine Cuttings: Effects of Rooting Solution and Full-Sib Family

Abstract

Abstract This research examined the effects of various rooting solutions and full-sib families on the rooting ability and subsequent growth and morphology of dormant loblolly pine stem cuttings set directly into open nursery beds. Two recommended concentrations of a commercial rooting compound (Woods Rooting Compound®), 9 and 17% (10:1 and 5:1 dilutions, respectively), and a water control in combination with four boron and four thiamine concentrations were tested. The 9% concentration contained 924 ppm indole-3-butyric acid (IBA ) + 594 ppm α-naphthaleneacetic acid (NAA) while the 17% concentration contained 1751 ppm IBA + 1122 ppm NAA. Family, rooting compound concentration, and their interaction were significant, while boron and thiamine main effects were not significant for percent rooted nor other traits assessed. Overall, 75% of cuttings treated with the water control rooted while cuttings receiving the 9 and 17% rooting compound concentrations rooted at 64 and 55%, respectively. However, the root systems of cuttings receiving the rooting compound treatments were more symmetrical, more vertically oriented and had greater dry weights than cuttings receiving the water control treatment. In addition, basal stem caliper and shoot dry weight, as well as the root:shoot ratio, were greater for cuttings receiving the rooting compound treatments. The trade-offs between rooting percent and root system morphology were addressed by investigating treatment differences in final crop yields as a percent of cuttings set. When seedling caliper standards were used as the grading criteria, no rooted cuttings were culled. Under this scenario, the water control treatment yielded the highest percent of acceptable (combined Grades 1 and 2) rooted cuttings (75%) since it also yielded the highest rooting percent. The range in yield of acceptable rooted cuttings for the five full-sib families receiving the water control treatment was 58 to 84%. When additional root system standards were imposed upon the caliper grades, the 9% rooting compound concentration yielded the highest percent of acceptable rooted cuttings (53%). The range in acceptable yields of the five full-sib families receiving the 9% rooting compound treatment when the additional root system grading standards were imposed, was 35 to 79%. A better understanding of the trade-offs between rooting percent and root system morphology as well as the effect of root system morphology on long-term growth of cuttings is needed. However, the rooted cuttings produced in this study by directly setting cuttings into open nursery beds exceeded commonly used seedling grading standards. While production costs were not addressed in this study, and significant additional development is needed, these results provide encouragement that an economical system of rooting loblolly pine cuttings in open nursery beds may be feasible. South. J. Appl. For. 23(2):108-115.