Optimization of Indole-3-Acetic Acid and Cutting Type for Enhanced Vegetative Propagation of Vetiver (Vetiveria zizanioides L.)

Vegetative propagation is a key method for the rapid multiplication and establishment of vetiver (Chrysopogon zizanioides). However, its success is often limited by poor rooting making the use of plant growth regulators such as indole-3-acetic acid (IAA) essential for improving propagation efficiency. This study evaluated the effects of different concentrations of IAA on the vegetative propagation of three types of vetiver cuttings: semi-hardwood (SHW), semi-softwood (SSW), and tillers. This was aimed at identifying the optimum concentration of IAA for rooting and growth of vetiver as well as determining the best cutting type for effective propagation of the plant, with a view to enhancing its vegetative propagation. The experiment was a 3 × 10 factorial arranged in a completely randomized design with seven replications. Cuttings were treated with 10 different IAA concentrations ranging from 0 to 100 ppm. Parameters assessed included root initiation period, number of newly formed tillers, number of leaves and leaf length, number of roots and root length, and dry weights of leaves and roots. Data generated were analyzed with SPSS 20 and significant means were separated using Fisher’s Least Significant Difference at p<0.05. Results showed that application of IAA reduced significantly (p<0.05) period of root initiation from 35 days in the control to 3-13 days in the IAA-treated cuttings with 25 ppm having the shortest root initiation period. In addition, IAA significantly (p<0.05) enhanced all the growth parameters assessed compared to untreated controls, with 25 ppm consistently yielding the best results. At this concentration and when averaged across all treatments, highest number of newly formed tillers (15), number of leaves (82), leaf length (115.35 cm), number of roots (95), root length (68.30 cm), and dry weights of leaves (1.81 g) and roots (1.77 g) were recorded. Higher IAA concentrations (>35 ppm) generally led to reduced growth and biomass production. Among the various cuttings, the tillers consistently outperformed SHW and SSW across all parameters. These findings show that moderate concentrations of IAA, particularly 25 ppm, significantly improved vegetative propagation efficiency and establishment of vetiver, with tillers being the best cutting type.