Ecophysiology and Micropropagation of Bigtooth Maples

Rolston St. Hilaire, Emad Bsoul, and Clare Bowen-O’Connor
Department of Agronomy and Horticulture
New Mexico State University
Las Cruces, New Mexico, USA 88003; e-mail: rsthilai@nmsu.edu

Background
Bigtooth maple (Acer grandidentatum Nutt.) is a potentially useful tree for managed landscapes. The plant tolerates drought and alkaline soil conditions (Barker, 1975) and is valued for its fall color. Although several ecological traits suggest that the plant merits more use in managed landscapes, bigtooth maple is not in widespread landscape use (St. Hilaire, 2002). Information on the relative drought tolerance of bigtooth maple is limited.

Conventional propagation techniques for bigtooth maples have produced mixed outcomes. The plant shows graft incompatibility on a standard sugar maple rootstock (Kuhns, 1998). While stem cutting propagation yielded only 0.8% rooting (Tankersley, 1981), stem layering (French technique) produced 71% rooting after seven months. Roots only formed from two-year-old, stem-layered shoots (Tankersley, 1981). Mound layering produced 20% rooting (Tankersley, 1981). Horticulturists must seek propagation strategies that eliminate the need for grafting and allow for effective and consistent multiplication of trees with desirable traits.

This paper presents 1) an experiment that characterized and compared drought responses of bigtooth maples indigenous to Texas, New Mexico, Utah and Arizona, and 2) another experiment that used tissue culture to enhance shoot and root development from single node explants of bigtooth maple.

EXPERIMENT 1: DROUGHT RESPONSES OF BIGTOOTH MAPLE

Materials and Methods
Samaras of bigtooth maple were obtained from 15 locations (Table 1), cold, moist stratified and grown in a greenhouse at New Mexico State University. The experimental design was a randomized complete block with seven blocks, 15 sources and two irrigation treatments (drought and control). Control plants were irrigated every other day with tap water. Plants in the drought treatment were irrigated when container weight decreased by 56 to 57%. Plants were subjected to cyclic drought. Physiological measurements were taken on the day a drought cycle ended. After 117 days of drought treatment, the experiment was terminated and plant growth and developmental traits were taken.

Table 1. Locations of the bigtooth maple seedlings used in this study.
LocationTree SourceLat. (N)Long. (W)
Dripping Springs State Park, New MexicoDS32.389106.813
Lost Maples Park, TexasLMP129.4099.350
LMP229.49099.350
LMP329.49099.350
LMP429.49099.350
LMP529.49099.350
Guadalupe Mts. National Park, TexasGM131.900104.867
GM231.900104.867
GM331.900104.867
GM431.900104.867
North & West slope of a wooded area, UtahUN141.460110.490
UN241.460110.490
UW141.460110.490
UW241.460110.490
Chiricahua National Forest, ArizonaAZ32.004109.356

Results and Discussion
After 117 days of drought treatment, well-watered seedlings of one tree source in Lost Maples Park (LMP1) in Texas had among the highest net assimilation rates. A relatively high net assimilation rate in LMP1 in well watered plants suggests these plants were relatively efficient in accumulating dry matter. When environmental conditions such as drought do not severely limit plant growth, rapid growth could be a useful trait for a landscape tree (Balok and St. Hilaire, 2002).

Plants from the tree originating from the Dripping Springs State Park (DS) and from trees designated as GM3 and GM4 of the Guadalupe Mountains showed large root dry matter accumulation in both droughted and well-watered treatments. Plants that maintain growth during drought might be a good selection trait for bigtooth maples. Seedlings from one tree in the Guadalupe Mountains (GM1) had among the lowest transpiration rates. Seedlings from Dripping springs (DS) showed high stomatal conductance. Predawn and midday leaf water potential were different between irrigation treatments and both among and within seed sources. Plants from one tree in the Guadalupe Mountains (GM3) had among the lowest leaf water potential. We conclude that the Guadalupe Mountains in Texas might be a good provenance to select bigtooth maples for arid environments.

EXPERIMENT 2: In Vitro Shoot Development of Bigtooth Maple

Materials and Methods
Sixty-five two-year old seedlings were selected from 13 sources within New Mexico, Texas and Utah. Seedlings were grown from seeds that were cold, moist-stratified and then germinated. Plants were grown in 3 gallon plastic pots filled with perlite (SunGro Hort., Bellevue, Wash.) and Canadian sphagnum peatmoss (SunGro Hort., Bellevue, Wash.), 1:1 by volume.

For shoot induction, explants were selected from three zones of the donor seedlings which were designated as basal, intermediate and terminal. Explants were kept under 40 Fmols/sq. m/s and 28 C. Explants were rapidly transferred (every two days) and washed with 1% ascorbic acid for 10 minutes to lower the level of tissue exudates. The Driver-Kuniyuki Walnut (DKW), Linsmaier-Skoog (LS ), Murashige-Skoog (MS), and Woody Plant Medium (WPM) tissue culture media were evaluated to determine the optimum media for shoot proliferation. Explants were stored in a completely randomized design and transferred every 30 days for 120 days. The number of shoots, color of leaves and callus size were recorded at the end of each 30-day transfer period.

Roots were induced by using media with and without auxin (IAA). Rooted plantlets were transferred to large plastic enclosures and hardened off for transfer to the greenhouse. Rooted plantlets were potted in a growing substrate of 1 perlite : 1 peatmoss (by vol.).

Results and Discussion
Shoot proliferation was successful for 18% of the initiated explants. Regardless of the zone of origin (P = 0.3055) of the explants, media had a positive effect on shoot proliferation (P = 0.0042). Of the four media used, DKW plant media showed the most promise for the micropropagation of bigtooth maple. Shoot proliferation averaged 10 shoots per explant for all sources on this media. Foliar pigmentation, expressed in 29% of all explants, ranged from red-purple to orange-red and varied by media. Whether pigment development provides clues to fall foliage color development needs further testing. Roots were induced on the basal portions of the explants after the 15-day induction. Rooting at the basal portions of the explant provides suitable plantlets for acclimation to greenhouse conditions.

Literature Cited

Barker, A. 1975. Acer grandidentatum and its propagation. Comb. Proc. Int. Plant Propag. Soc. 25: 33-38.

Kuhns, M. 1998. Trees of Utah and the Intermountain West. Utah State University Press, Logan.

St. Hilaire, R. 2002. Bigtooth maple: A plant that merits more use in Southwestern landscapes. Landscape Plant News 13:10-11.

Tanskersley, B. E. 1981. Growth and propagation of Acer grandidentatum Nutt. MS Thesis. Texas A & M Univ., College Station.