Stock plant management of Lavandula angustifolia 'Wee One' using plant growth regulators and propagation techniques used to create optimal protocols for several Plant Select® species

Abstract

2021 Spring.Includes bibliographical references.Lavandula angustifolia 'Wee One' is a drought tolerant dwarf herbaceous perennial being promoted by Plant Select®. The increased demand for this herbaceous perennial has resulted in problems with stock plant management and propagation due to the relatively small vegetative growth. The objective of this study was to determine the effects of plant growth regulators applied as foliar sprays on the vegetative growth of Lavandula angustifolia 'Wee One' propagation stock plants. Five chemical plant growth regulators were applied at the optimal recommended rates : 1) Ethephon (2-Chloroethyl) phosphonic acid [500 mg·L-1 (ppm)] (Verve, Nufarm Americas, Inc., Alsip, IL). 2) Kinetin, Gibberellic Acid, Indole-3-butyric Acid [500 mg·L-1 (ppm)] (Gravity, Winfield Solutions, LLC, St. Paul, MN), 3) N-(phenylmethyl)-IH-purine 6-amine, Gibberellins A4A7 [100 mg·L-1 (ppm)] (Fascination, Valent USA Corp., Fresno, CS), 4) N-(phenylmethyl)-1H-purine-6-amine [400 mg·L-1 (ppm)] (Configure, Fine Agrochemicals Limited, Worcester, U.K.), 5) Gibberellin A3 [100 mg·L-1 (ppm)] (ProGibb T&O, Valent USA Corp., Fresno, CS). Fifteen replications of Lavandula angustifolia 'Wee One' were evaluated once for four months for plant height, width, number of cuttings, and fresh & dry weight of the cuttings. This study was replicated twice, the first experiment was performed from March 2020 to July 2020 and the second experiment was performed from August 2020 to December 2020. Lavandula angustifolia 'Wee One' stock plants that were treated with ProGibb T&O at 100 mg·L-1 (ppm) resulted in larger stock plants with more cuttings produced. A secondary rooting study was conducted at the same time of each experiment. Cuttings were taken at the same time of day and stuck in trays of 26-strip Jiffy® Preforma media and placed under mist with bottom heat at a temperature of 23.9°C. Number of visible roots and rooting percentages were then recorded every week for four weeks. Rooting of Lavandula angustifolia 'Wee One' resulted in no observed differences between plant growth regulator treatments and the control. In conclusion, the use of plant growth regulators resulted in increases of propagation material for Lavender stock plants. Foliar applications of ProGibb T&O at 100 mg·L-1 (ppm) caused an increase in growth of vegetative material and increased the number of cuttings produced from each stock plant with no decreases in the rooting percentage of those cuttings. Epilobium canum subsp. garrettii 'PWWG01S', Osteospermum species, and Pterocephalus depressus are three herbaceous perennials being promoted by Plant Select®. The increased demand for these perennials has resulted in problems with current propagation protocols and production of rooted cuttings. The objective of the propagation techniques study was to determine the optimal combination of rooting hormone, root zone heating temperature, and hormone application methods that would result in higher rooting percentages of cuttings in four weeks. The first experiment focused on two concentrations of Dip N Grow rooting hormone applied to a cutting and placed on two different root zone heating temperatures. Three replications of this experiment occurred from July 2019 to September 2019. The second experiment focused on two rooting hormones (Dip N Grow and Hortus IBA) applied at a single concentration with two different application methods of quick dip (30 seconds) or immersion (3 minutes). Two replications of this experiment occurred from February 2020 to March 2020. After these two experiments, recommendations for propagation protocols can be written. Pterocephalus depressus prefer quick dip application of 30 seconds with either rooting hormone at 500 mg·L-1 (ppm) at a 23.9°C root zone heating temperature. Osteospermum species prefer an immersion application of 3 minutes with Dip N Grow at 500 mg·L-1 (ppm) at a 20°C root zone heating temperature. Epilobium canum subsp. garrettii 'PWWG01S' prefer a quick dip application of 30 seconds with either hormone at 500 mg·L-1 (ppm) with a root zone heating temperature of 20°C. All these recommended propagation techniques resulted in faster rooting and higher rooting percentage when compared to the untreated controls