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NMSU scientists develop in vitro method to produce hard maples

It's a difficult process to reproduce hard maples, but researchers at New Mexico State University studying the bigtooth maple as a landscape ornamental plant have developed a micropropagation method that has a better success rate than traditional methods.

NMSU graduate research assistant Clare Bowen-O'Connor dissects a bigtooth maple sprout that has been grown in vitro as fellow researchers Cynthia Killough, Professor Rolston St. Hilaire, Victoria Frietze and Santos Barron watch. (NMSU photo by Darren Phillips)

"There has not been success in micropropagation hard maples until now," said Rolston St. Hilaire, associate professor in the NMSU Plant and Environmental Sciences Department, of the research conducted by graduate research assistant Clare Bowen-O'Connor. "This is a significant accomplishment for producing bigtooth maples for the landscape industry, as well as for us as we continue our genetic research in the plant known for its colorful fall foliage."

Traditionally, the bigtooth maple, which is normally found as a large shrub or small tree growing on moist canyon sides and mountain sites, is reproduced by seed or grafting to sugar maple roots. But this grafting method has only a 1 percent success rate, St. Hilaire said. Now researchers and nursery growers can start the plants in vitro with buds cut from established trees.

"This is an important achievement for the hard maples because they are so difficult to propagate in general," Bowen-O'Connor said. "Our method will allow the maintaining of set traits, such as beautiful color, good form, and resistance to disease and iron deficiency, which are required by the landscape industry."

A paper reporting on the micropropagation process will be published in an upcoming issue of In Vitro Plant, a journal produced by the Society for In Vitro Biology. Also, the paper and lab will be featured separately in In Vitro Report, another journal produced by the society.

Bowen-O'Connor authored the paper describing research she conducted with John Hubstenberger, Cynthia Killough, Dawn Marie VanLeeuwen and St. Hilaire.

"This is a good accomplishment for Clare to be published in a publication that is among the top 30 percent of all biology journals," St. Hilaire said. "It demonstrates that her research was a solid piece of work and was selected as a journal highlight for its quality of work."

During the two-year study, it was determined that the bigtooth maple can be efficiently micropropagated using axillary buds, those found in the angle between the upper side of a leaf or stem and the supporting stem or branch, from greenhouse-grown seedlings. The double-node microshoots were rooted in vitro on Driver-Kuniyuki Walnut tissue culture containing a plant growth regulator that provided nutrients to the plant.

The shoot sprouting and proliferation was observed for 180 days. Once the roots were developed, the shoots were successfully transferred to a growing substrate of perlite and peatmoss.

"Although only 15 percent of the shoots rooted, our micropropagation protocol is one way to provide a selected number of bigtooth maple clones," Bowen-O'Connor said. "Our technique shows that you can clone and propagate the plant in a small area. If you have limited space but need to get a lot of samples out, this method can do that."

She added the method may be used in a nursery setting where the growers are interested in maintaining particular traits, or if researchers want to study a particular population without having to wait a year for more seeds to be produced. "You can do more research, more quickly," she said.

Micropropagation is the second step of research under the direction of St. Hilaire, who has experimented with maples at NMSU and Iowa State University for 12 years. The researchers have been working for the past five years to develop the bigtooth maple for use by the landscaping industry. Currently the tree is found only in mountain canyons, such as the Manzano Mountains' Fourth of July Canyon in New Mexico.

"Bigtooth maple is indigenous in 11 states, including parts of New Mexico, Arizona, Texas, Oklahoma and Utah. However, it isn't widely used in New Mexico home or commercial landscapes because the one variety available is difficult to grow," he said. "We are working to overcome that difficulty because the bigtooth maple is a desirable ornamental tree with fall foliage color that ranges from yellows and oranges to crimson. The plant is slow growing, which makes it well suited for small landscape spaces."

The first step of the research, after growing seedlings from seed specimens gathered from 36 locations in the Southwest, was to determine if the plant is drought and salinity tolerant. Research conducted by Emad Y. Bsoul, a former graduate research assistant who is now an assistant professor of biology at Hashemite University in Jordan, found a few promising candidate, according to St. Hilaire.

The next step in the research is to determine the plant's genetic markers. St. Hilaire is currently on a five-month sabbatical at the U.S. Department of Agriculture's Agricultural Research Center in Beltsville, Md., where he is working to decipher the genetics of the various populations collected in the study.

St. Hilaire cautions that a drought-tolerant maple variety won't be available overnight. While several promising specimens have been selected, a new tree for New Mexico is probably more than a decade away.

"These are relatively slow-growing trees, not row crops," he said. "It's a long-term effort, but one that has tremendous economic potential. Plus there's the promise of stunning red and yellow trees sweeping across the landscape each fall for future New Mexicans."