2017 ASHS Annual Conference

Crape myrtles are a dependable source of color in many southern landscapes, and the list of useful cultivars is constantly growing. Mississippi State University has been active in the development of new crape myrtle selections, including ‘Tishomingo’. This new crape myrtle is a cross between Lagerstroemia ’Tonto’ and L. ’Catawba’. Flowers are a clear medium to dark purple, and the plant has a medium to large growth habit. The objective of this research was to determine optimal commercial auxin formulation and concentration for hardwood cutting propagation of ‘Tishomingo’. 12.7-cm medial cuttings were harvested from the parent plant and stuck to a depth of 2.5 cm on 1 Feb. 2017. Propagation medium was 100% perlite placed in 7.6-cm containers. Treatments included two basal treatments (wounded or non-wounded), three auxin formulations [Hortus IBA (Hortus IBA Water Soluble Salts), Dip’N Grow, or Hortus IBA + KNAA (Hortus IBA Water Soluble Salts + NAA potassium salt)], and three levels of auxin (0, 1000, or 5000 ppm IBA). Dip’N Grow and Hortus IBA + KNAA formulations contained NAA at one-half the rate of IBA. The experimental design was a randomized complete block design with five single cutting replications. Data collected after 63 days included rooting percentage, growth index (new shoots), cutting quality (0-5, with 0 = no roots and 5 = transplant-ready cutting), total root number, average root length (of three longest roots), and root quality. Data were analyzed using linear mixed models and generalized linear mixed models with the GLIMMIX procedure of SAS (ver. 9.4; SAS Institute Inc., Cary, NC). Treatment comparisons were as follows: wounded vs. non-wounded, Hortus IBA vs. no auxin, Dip’N Grow vs. no auxin, Hortus IBA + KNAA vs. no auxin, Hortus IBA vs. Dip’N Grow, Dip’N Grow vs. Hortus IBA + KNAA, Hortus IBA vs. Hortus IBA + KNAA, Hortus IBA at 5000 vs. 1000 ppm IBA , Dip’N Grow at 5000 vs. 1000 ppm IBA, and Hortus IBA + KNAA at 5000 ppm IBA vs. 1000 ppm IBA. Treatment had no impact on rooting percentage, root count, average of three longest roots, root quality, or cutting quality. These results suggest that hardwood cuttings of ‘Tishomingo’ crape myrtle can be successfully rooted without wounding or use of an auxin treatment.