2018 ASHS Annual Conference

Guayule is a desert-adapted woody perennial, having been used as a landscape plant and presently being commercialized for rubber production. It is difficult to establish guayule from seed, and an alternative method of propagation is by cuttings. Success in this process is dependent on multiple environmental and endogenous factors, including: humidity, media, age of cutting material, and hormone treatment. The factor manipulated in this study was auxin. The hypothesis was a low concentration of auxin would have minimal effect on rooting, and a high concentration would have a negative effect. A range of 500 ppm to 2000 ppm (in steps of 500 ppm) of Indole Butyric Acid (IBA) in solution with water were tested. The same range was applied with Napthaleneacetic Acid (NAA). Many commercial rooting hormone products use a mix of IBA and NAA, so one treatment of 750 ppm IBA:750 ppm NAA treatment was included. A DI water treatment was the control. The cutting material was late first-year growth from shoot tips, cut between 6-9 cm, and the bottom two-thirds stripped of foliage. The cuttings were treated in batches of 10; the basal cuts dipped into a treatment solution, agitated for 10 seconds, and allowed to soak for another 50 seconds. Cuttings were planted approximately 5 cm deep in a media of 1:1 coco coir and perlite. A total of 1,600 cuttings, for the 10 treatments, 4 varieties (AZ-3, R1100, 593 and 11693), and 4 reps were treated. Each repetition was fitted into two plug-trays, for a total of 400 cuttings. Each treatment was randomly assorted into a 2x5 cell region of the tray. After 46 days, the cuttings were scored: 0 – dead, 1 – no change, 2 – cell differentiation (but no rooting), 3 – root initiation, 4 – 1/3 of plug rooted, 5 – 2/3 of plug rooted, 6 – fully rooted plug. Just considering total number rooted (rooting scores of 4, 5, and 6 combined), there were few differences among auxin treatments. That the treatments were generally not different from water, the auxin concentrations were neither high or nor low enough to confirm the hypothesis. There were significant differences among lines for treatments. Lines 593 and R1100 produced fewer roots in comparison to AZ-3 and 11693. The combination IBA:NAA treatment produced a higher number of rooting scores of 5 and 6. Thus, the experiment is continuing by testing different ratios of IBA:NAA, and varieties AZ-3 and 11693.