HORTSCIENCE 55(9):1463–1467. 2020. https://doi.org/10.21273/HORTSCI15212-20 Since the introduction of IBA more than 70 years ago, it has been the subject of hundreds of publications. A greater ability of IBA to Highly Successful Adventitious Root promote AR compared with indole-3-acetic acid may in part be to its greater stability Formation of Zamia L. Stem Cuttings (Hartmann et al., 1990). Several propagation studies with cycad Exhibits Minimal Response to Indole-3- species have employed the use of IBA. For example, Z. integrifolia plants that had the zygotic taproot severed and dipped in 2–4 Butyric Acid mg·g–1 IBA usually produced two or more Benjamin E. Deloso roots to replace the severed section of the Western Pacific Tropical Research Center, University of Guam, UOG taproot (Dehgan, 1983; Dehgan and Johnson, 1987; Dehgan et al., 1994). Large C. micro- Station, Mangilao, Guam 96923 nesica stem cuttings from unhealthy trees Anders J. Lindstrom€ exhibited moderate rooting success, and large stem cuttings from healthy trees exhibited Nong Nooch Tropical Botanic Garden and Resort, Chonburi, Thailand 100% success when the cut end was dipped in 20260 a commercial 3 mg·g–1 IBA product (Marler and Cruz, 2017a; Marler, 2018c). Pups of Frank A. Camacho and Thomas E. Marler three Cycas species exhibited AR formation College of Natural and Applied Sciences, University of Guam, UOG Station, of 75% to 92% with the use of 3 mg·g–1 IBA Mangilao, Guam 96923 (Marler et al., 2020). These studies on asexual propagation of Additional index words. asexual propagation, cycad, IBA, Zamia furfuracea, Zamia cycads illuminate the success and relative integrifolia ease of propagation using commercial IBA Abstract. The influences of indole-3-butyric acid (IBA) concentrations of 0–30 mg·gL1 on products. However, to our knowledge there the success and speed of adventitious root development of Zamia furfuracea L.f. and have been no published IBA dose response Zamia integrifolia L.f. stem cuttings were determined. Root formation success for both studies for any cycad species. Moreover, species was greater than 95%. The IBA concentrations did not influence the speed of root most of the 356 described cycad species development for Z. furfuracea, but the Z. integrifolia cuttings that received IBA (Calonje et al., 2020) have not been repre- concentration of 3 mg·gL1 generated adventitious roots more slowly than the cuttings sented in the asexual propagation literature. in the control group. The ending dry weights of the stems, leaves, and roots were not Our objective was to determine the influence · –1 influenced by IBA concentration for either species. Our results indicated that adventi- of IBA concentrations of 0 to 30 mg g on tious root formation on stem cuttings of these two Zamia species is successful without the success and speed of adventitious root horticultural application of IBA. Additional IBA studies are needed on the other 300+ formation on Z. furfuracea and Z. integrifolia cycad species, especially those that are in a threatened category. stem cuttings. Materials and Methods The role of horticulture in the conserva- seed plants whose origins have been traced tion programs of rare plant species and hab- back to the late Paleozoic era (270–250 mya), Seedlings aged six years old of the Mex- itat restoration has become increasingly reaching their maximum worldwide diversity ican cycad Z. furfuracea in 210-mL tubes were used to make stem cuttings for a repli- important in recent years (Marler, 2017). during the Jurassic era (193–136 mya) The skills of horticulturists are uniquely cated propagation study at the University of (Jones, 1993; Mamay, 1969; Norstog and Guam. The experiments were repeated with suited for plant conservation work (Kay Nicholls, 1997). Due to their ancient origins et al., 2011). Proficient horticultural practices seedlings aged six years old of Z. integrifolia, and attractive forms, cycads have become may particularly benefit plant species that are a related species native to the southeastern threatened with extinction or nearing extir- more popular in the horticulture trade and are United States. These model species were pation in the wild. Cycads are the most becoming more commercially available. chosen based on local availability, abundance endangered group of plants worldwide, with Sexual and asexual methods of cycad in the nursery trade, and relative ease of more than 63% of described taxa listed under propagation have been used in the horticul- horticultural care. one of the threatened categories (Brummitt ture industry. Both methods were reviewed Plants without noticeable active leaf ex- et al., 2015; Fragniere et al., 2015). Cycads by Dehgan (1983, 1999) outlining the advan- pansion were used. All leaves were pruned at are a geologically primitive extant group of tages and disadvantages of each method. the base of each petiole, and the zygotic Some cycad species produce adventitious taproot was cut at the base of each stem to stems especially near the base of the main remove all root tissue and expose a clean cut stem, and these are known as ‘‘pups’’ at the base of each stem. This is an unambig- Received for publication 3 June 2020. Accepted for (Norstog and Nicholls, 1997; Stopes, 1910; uous endeavor because vascular tissue ar- publication 29 June 2020. Tang, 1985). Adventitious roots (AR) are rangement differs in stem and root tissues and Published online 31 July 2020. often induced on these detached pups during can be easily observed on the open wound Financial support was provided by the U.S. Forest successful asexual propagation protocols. (Marler et al., 2010). Water pressure was Service and the Western Pacific Tropical Research Additionally, some cycad species such as used to clean the stems, then they were air Center, University of Guam. Cycas micronesica K.D. Hill that are adapted dried for 30 min. The fresh weight of each We thank Frankie Matanane and Charles Paulino to frequent tropical cyclones may form nat- stem cutting was recorded. for assistance with maintaining the experimental ural vegetative propagules after falling, Each stem cutting was first dipped in 10% units and for help with preparation of the stem where they subsequently form adventitious bleach solution (The Clorox Company, Oak- cuttings. B.E.D. is the corresponding author. E-mail: delosob@ roots at the points of soil contact with the land, CA), then in a 0.13% Daconil fungicide triton.uog.edu. stems (Marler and Cruz, 2017b). solution (Techpac LLC, Atlanta, GA), then This is an open access article distributed under the The synthetic auxin IBA was among the surface water was allowed to air-dry. The CC BY-NC-ND license (https://creativecommons. first plant hormones used for enhancing root Hormex root stimulant powder (Brooker org/licenses/by-nc-nd/4.0/). formation on plant stems (Cooper, 1935). Chemical Corp., Chatsworth, CA) was used HORTSCIENCE VOL. 55(9) SEPTEMBER 2020 1463 as our source of IBA. The cut end of each of root formation without disturbing the per- for the control and 16 mg·g–1 plants, and stem was dipped into one of the concentra- lite or cuttings. 100% for the 3, 8, or 30 mg·g–1 plants. tions: 0, 3, 8, 16, or 30 mg·g–1. The exposed Each individual rooted cutting was re- The Z. integrifolia IBA study lasted 356 d, parenchyma was then covered with a com- moved from the perlite at the time of root from July 2018 to June 2019. The mean high mercial tree sealant and air dried for 24 h. contact with the container’s bottom surface, temperature during this study was 33.9 ± Clear 2.84-L Cambro containers (Cambro then was planted into 2.6-L containers filled 2.4 °C, while the mean low temperature was Manufacturing Company, Huntington Beach, with a medium consisting of 50% sunshine 26.0 ± 1.2 °C. The days to first root contact CA) were used for the study. One container mix #4: 25% #16 sand: 25% field soil. This differed among the dose levels (P = 0.033), was designated as a replication that contained medium had about equal volumes of peat, and the control group (0 mg·g–1 IBA) re- one cutting per IBA dose level, with five stem perlite, sand, and soil. Other nondestructive quired an average of 56 d to root, compared cuttings per replication, for a total of 25 variables were also recorded throughout the with the 3 mg·g–1 IBA treatment, which replications. Similarity in stem diameter duration of the experiment. These included required an average of 77 d (Fig. 2). The 8, was used to select the five cuttings for each factors such as the date of first leaf emer- 16, and 30 mg·g–1 plants did not differ from replication. The containers were prepared gence, the date of cutting death (if mortality the 0 or 3 mg·g–1 plants in speed of root with drainage holes drilled 5.5 cm apart to occurred), and the overall appearance of the formation. The IBA treatments did not influ- ensure that each stem cutting was positioned AR system at the time of removal from ence root dry weight, stem dry weight, leaf with equal spacing from each other and at a perlite. Photographs were used to aid in this dry weight, coralloid root cluster number, or homogeneous distance to drainage holes. endeavor. initial leaf emergence (Table 1). The percent Perlite (Therm-O-Rock West, Inc, Chan- The plants were maintained until the final rooting success (not subjected to ANOVA) dler, AZ) was filled to the 2.37 L level, with cutting in each experiment produced AR or was 100% for the control and 30 mg·g–1 5.5 cm between the bottom of each stem was identified as dead.