Effects of seasons and indole-3-buteric acid doses on the propagation of some native rhododendron species by air layering technique in their natural habitats

Abstract

This research was conducted to determine to the effects of indole-3-butyric acid (IBA) doses and propagation season on rooting rates and some root parameters of Rhododendron species, R. ponticum L., R. luteum Sweet, R. ungernii Trautv, and R. caucasicum Pallas. Air layering technique and IBA doses (0, 500 ppm, and 1,500 ppm) were applied to each Rhododendron species in their natural habitat in autumn and spring. In the present investigation, dry root weight (mg), root length (cm), root volume (cm3), and root diameter (mm) were investigated as root quality parameters. The highest rooting efficiency (100%) was obtained from R. caucasicum and R. ungernii species. The rooting efficiencies of R. ponticum (between 6.67% to 66.67%) and R. luteum (between 0% to 53.33%) species were lower than the other two species. The heaviest dry root (266.10 mg), the largest root volume (1.49 cm3), and the thickest root diameter (0.05 cm) were obtained in autumn and 1,500 ppm IBA dose from R. caucasicum species. The longest roots, 349.21 cm, were formed in the R. ungernii species in the spring, during the air layering, in which 500 ppm IBA dose was applied.