Propagation of Ilex vomitoria ‘Dare County’ by Stem Cuttings

Nontreated semi-hardwood stem cuttings of ‘Dare County’ yaupon holly will root at > 75% whereas hardwood cuttings root poorly regardless of K-IBA treatment. Treatment of semi-hardwood cuttings with K-IBA will decrease percent rooting.

Ilex vomitoria Sol. ex Ait. (Aquifoliaceae Bartl.) (yaupon, cassena, Christmas berry, or evergreen holly) is a dioecious, evergreen species native from southeast Virginia to central Florida and west to Oklahoma and Texas (2, 11). Growth habit can vary from a small to large upright shrub or a small tree. New growth in the spring has a purple cast that is soon lost becoming a lustrous, dark green.

Female plants of I. vomitoria are particularly attractive in mid fall to spring as they often bear copious quantities of colorful fruit on 1-year-old wood. The fruit are globose drupes approximately 0.6 cm (0.25 in) in diameter with each fruit containing four pyrenes (nutlets) (11). Drupe color is normally red to scarlet and there are selections with yellow or orange fruit (3).

The species is very adaptable as it will tolerate extremely dry to wet soils. It is also tolerant of salt spray and is frequently used in coastal landscapes. Owing to its adaptability to various site conditions and the large number of cultivars of various growth forms (3), I. vomitoria is a popular landscape plant in the southeast United States.

One outstanding cultivar of I. vomitoria is a female selection, ‘Dare County’ (syn. ‘Virginia Dare’). ‘Dare County’ yaupon holly is a stiff and divergently large shrub or small tree. As a tree it can reach heights > 7 m (23 ft) with a spectacular fall and winter fruit display of reportedly orange drupes that persist into spring. Despite having considerable landscape merit, little if any information has been published regarding propagation of this cultivar other than it can be propagated by stem cuttings (7).

Cultivars of I. vomitoria are generally propagated vegetatively by stem cuttings although as reported by Dirr and Heuser (4), rooting of cuttings can be ‘reasonably difficult.’ Also, the growth stages of stock plants that are most conducive to rooting appear to be semi-hardwood or hardwood (1, 4) although ‘Nana’ yaupon holly can be propagated by softwood cuttings (5). Therefore, the following research was conducted to determine the influence of stock plant growth stage and auxin treatment on propagation of ‘Dare County’ yaupon holly by stem cuttings.

Two hundred terminal stem cuttings approximately 10 to 12 cm (3.9 to 4.7 in) in length were taken September 10 and December 17, 2009, and March 4, 2010, from a tree of ‘Dare County’ holly growing in a roadside planting of other Ilex L. (holly) sp. in Manteo (Roanoke Island), NC. The tree was multi-stemmed with an approximate height and width of 7.6 and 9.1 m (25 and 30 ft), respectively. Cuttings taken September 10, 2009, were semi-hardwood having stems that were tan to light gray in color. When pressure was applied to a cutting the stem broke, sometimes with a snapping sound, but the pieces remained attached at the point where pressure was applied. Cuttings taken December 17, 2009, and March 4, 2010, were hardwood. Stems of the December 17 cuttings were similar in color and lignification to the semi-hardwood cuttings of September 10. The lower two-thirds of the stems of hardwood cuttings taken March 4, 2010, were light gray in color; the upper third reddish purple. When pressure was applied to the stem it broke with a snapping sound and the pieces held together at the point where pressure was applied.

The semi-hardwood cuttings and the December 17 hardwood cuttings consisted of the current season's growth whereas the hardwood cuttings of March 4, 2010, consisted of growth which occurred the previous season in 2009. When cuttings of both stages were taken, prolific fruit development was observed on 1-year-old wood as flowering of I. vomitoria occurs in mid-April on this growth. However, the cuttings prepared for rooting did not include any of this older growth with fruit. Fruit color on September 10 was green. On December 17 fruit were yellow/gold in color, and on March 4, 2010, the fruit were orange. Following collection, cuttings of each growth stage were trimmed from the bases to lengths of 8 to 10 cm (3.1 to 3.9 in) and leaves removed from the lower 4 cm (1.6 in). They were then treated with solutions of the potassium (K) salt (K-salt) of indolebutyric acid (K-IBA) at 0, 2000, 4000, 6000, or 8000 mg·liter⁻¹ (ppm). Solutions were prepared by dissolving reagent grade K-IBA in distilled water.

When treating cuttings with K-IBA, the basal 2 cm (0.8 in) was dipped into the K-IBA solution for 2 sec followed by 20 min of air drying before inserting into the rooting medium. After auxin treatment, cuttings were inserted to a depth of 3 cm (1.2 in) in individual plastic Anderson bands (Anderson Tool & Die, Portland, OR) [6.0 × 6.0 × 12.7 cm (2.4 × 2.4 × 5.0 in)] held in deep propagation flats/trays [40.6 × 40.6 × 12.7 cm (16 × 16 × 5 in)] with 36 cells per flat (6 rows × 6 columns). The rooting medium was peat:perlite (1:1 by vol).

The trays were placed on a single raised bench under natural photoperiod and irradiance in a glass covered greenhouse on the campus of NC State University, Raleigh. Day/night temperatures were approximately 21.1 ± 2.8/18.3 ± 2.8C (70 ± 5/65 ± 5F). Intermittent mist operated 4 sec every 5 min from 7:00 am to 8:30 pm daily. The experimental design was a randomized complete block using six cuttings per treatment with six replications.

Fourteen weeks after the rooting studies were initiated, cuttings were harvested and data recorded. Data included the number and length of primary roots > 1 mm (0.04 in). Any cutting having one or more roots was classified as rooted. Data were subjected to analysis of variance procedures and regression analysis.

Nontreated semi-hardwood cuttings of ‘Dare County’ holly rooted at 78% (Table 1), whereas hardwood cuttings taken on two dates rooted in low percentages regardless of auxin treatment (data not presented). Combining all treatments, rooting of hardwood cuttings taken December 17, 2009, and March 4, 2010, was 11 and 15%, respectively, indicating such cuttings should not be used to propagate ‘Dare County’ yaupon holly. On the other hand, nontreated semi-hardwood cuttings appear to be an excellent means to propagate the cultivar. Treatment with K-IBA was either of no benefit or inhibited rooting. The only significant affect of auxin treatment was a linear decrease in percent rooting (P ≤ 0.05) whereas root number and root length were unaffected (Table 1).

There are two principal auxins used, either alone or in combination, to stimulate adventitious rooting of stem cuttings, indolebutyric acid and naphthaleneacetic acid (NAA). Both compounds are available as free acids or K-salts, the former being soluble in an organic solvent such as ethyl, methyl, or isopropyl alcohol and the latter being water soluble. In this research, we used solutions of the K-salt of IBA for treating stem cuttings since there are reports alcohol may injure cuttings of I. vomitoria (4) and ‘NAA will burn the stem and cause defoliation (9).’ Also, the range of K-IBA treatments selected to treat the cuttings was based on previous reports for the species (1, 4, 9).

The authors did not attempt to root softwood cuttings of ‘Dare County’ holly due to lack of sufficient cutting material. Also, most reports indicate I. vomitoria is best propagated by semi-hardwood or hardwood cuttings (1, 4) although one report indicates ‘Nana’ yaupon holly is propagated commercially by softwood cuttings (5). It would be useful to investigate propagation of ‘Dare County’ holly by softwood cuttings because if successful, this would provide another window of opportunity to root stem cuttings.

There appears to be considerable misunderstanding regarding the proper cultivar name of ‘Dare County’ holly and the color of mature fruit. The cultivar was discovered and selected by Bauers in 1978 from a population of six plants supposedly having orange colored fruit at maturity (7). The plant selected from the population reportedly had the most attractive fruit. The plants were growing at the Bodie Island National Seashore Park, Dare County, NC. When registered with The Holly Society of America in May 1985, the cultivar name was ‘Virginia Dare’ holly in honor of the first English child born 1587 in the Americas in what is presently Dare County, NC (7). Following registration with the Holly Society, it was determined the name, ‘Virginia Dare’, had been used and published previously for a selection of I. opaca L. (American holly) (6). The name ‘Virginia Dare’ was not valid and Bauers chose the name ‘Dare County’ (6, 7). Thus, ‘Virginia Dare’ is a synonym for ‘Dare County’ although many individuals still use the name ‘Virginia Dare’. There is also confusion regarding the color of mature fruit.

In a description of the cultivar published in 1985, mature fruit color was described as orange (7). However, a description of the selection included with the Holly Registration Certificate (Registration No. 6-85) submitted by Bauers and dated May 31, 1985, described the fruit as ‘translucent yellow/orange’ (11). We have observed fruit color can vary yearly and the color of mature fruit is not always orange. As the fruit develop they are initially green and as they mature in fall, they develop a yellow/gold color that in late fall sometimes changes to orange. Other years the fruit remain yellow/gold with only a trace of orange color. The variable color of the fruit from year to year is probably influenced by environmental/climatic factors. Regardless of the color of the fruit, the yearly fruit display is outstanding and extremely attractive.

Since June 2009 the authors have observed growth of the stock plant (tree) from which stem cuttings were taken in 2009 and 2010. To date no insect or disease problems have been observed with one exception. In December 2009 some leaf mining injury was observed and care taken not to remove cutting material having such injury. The injury was subsequently identified by the NC State Plant Disease & Insect Clinic as caused by Phytomyza vomitoriae Kulp [holly leafminer (Diptera: Agromyzidae)].

Adventitious roots of ‘Dare County’ holly, like other cultivars of I. vomitoria are fleshy, but fine textured and easily damaged even when rooted in a medium of peat:perlite (1:1 by vol), as in this research. Since the roots are prone to injury, the authors strongly advise that direct rooting/sticking be used when propagating ‘Dare County’ yaupon holly by stem cuttings as this should reduce potential transplant shock.