by Norman Martin DESERT PLANT MAY PUT SPRING IN NATURAL RUBBER PRODUCTION
LAS CRUCES
Stung by the September 11 attacks on the United States, consumers and companies alike are creating a run on protective gloves. One of the nation’s largest medical suppliers, Medline, reported a 40 percent jump in retail sales of exam gloves.
Now, it seems, a rubber-producing desert shrub that’s intermittently flickered across New Mexico’s scientific and industrial radars for more than 100 years may have a hand in improving future supplies.
Natural rubber from a Chihuahuan Desert plant with the tongue-twisting name of guayule (pronounced why-YOU-lee) holds strong potential as a source of high-quality, non-allergenic latex for medical, industrial and home products. Experts say cost-competitive latex from the native plant is free of allergens that can cause severe or fatal reactions, but provides an effective barrier against disease-causing bacteria and viruses.
“Guayule is a high-potential, high-risk crop,” said James Fowler, an agronomist at New Mexico State University, who has grown and studied guayule in New Mexico for more than 15 years.
Drought-tolerant and insect resistant, guayule is a yellow-flowered, silvery-leaved shrub that resembles sagebrush, he said. It grows about three feet tall in desert limestone soil at elevations of 2,000 to 6,000 feet. Natural rubber is produced in the plant’s woody stems and roots, said Fowler, superintendent of NMSU’s Leyendecker Plant Science Research Center in Las Cruces.
Rubber from the Brazilian Hevea tree is the most common source of natural rubber for gloves, catheters, condoms and many other medical, industrial and household products. But with 57 allergenic proteins in tropical rubber, it can produce symptoms that range from simple skin irritation to deadly anaphylactic shock.
It wasn’t until the mid-1990s that U. S. Department of Agriculture researchers made a breakthrough in extracting guayule’s latex. The process involves wet-grinding the plant into a sort of guayule milkshake. Because latex is lighter than water, it can then be separated, removed and purified. So far, plant breeders have pushed yields from less than 350 pounds of rubber per acre in the 1940s to almost 1,000 pounds of rubber per acre now.
Still, some old-time guayule watchers are wary of a plant that has seen more comebacks than Madonna. Many private and government commercialization attempts have fizzled since the turn of the last century. This time, though, backers are betting that the growing rates of latex allergies and the fact that it won’t be used solely for tire production will snap buyers into line.
Commercial guayule production is already rolling. San Diego, Calif.-based Yulex Corp., which has an exclusive licensing agreement with the federal government, is growing selected guayule seed lines in greenhouses and commercial farms in Arizona. It has experimental plantings at NMSU, the University of Arizona and Texas A&M University.
In a brief interview, Yulex CEO Jeff Martin said that in addition to commercial production of guayule rubber latex, there’s interest for guayule from the chemical industry and for adhesives, gums, and resins. Martin expects to manufacture and market the first guayule latex products in 2003, and by 2005 hopes to have more than 50,000 acres of guayule under contract, enough to supply about 10 percent of the latex used in the United States. Yulex’s crop, which is grown from transplants, has a two-year growth cycle.
Many scientists agree that the budding guayule industry may finally be moving toward sufficient yields to meet domestic demand for commercial latex. One reason for this optimism is the scope of academic interest. Since 1978, NMSU researchers have studied guayule, working with university teams in Arizona, California and Texas, and researchers with the U.S. Department of Agriculture.
As part of a $264,000 USDA-funded project, NMSU’s role is developing seed production technology, and improving the longevity and viability of the seed. The funding is part of a four-year, $2.3 million research grant that is expected to lead to commercial production of guayule rubber latex. The NMSU team is also screening pre-emergence herbicides for direct planting of guayule. Difficulty in getting seed started is one reason why Yulex turned to much more expensive greenhouse-grown transplants.
“Guayule is a difficult plant to work with,” Fowler said. The seed is fragile and small, and because guayule is a native desert plant, it has a natural dormancy defense that demands near perfect growing conditions before it will germinate. Other inhibiting factors to direct seeding are sensitivity to salt, a light requirement and very shallow planting depth.
Another research effort deals with getting the seed harvested and cleaned. “Much of the seed we harvest today is just an empty seed coat,” Fowler said. “A very small percentage of the material will actually have field viable seed – as low as 2 to 8 percent. We’re talking about dealing with a lot of material just to get a small amount of seed.”
The seed harvest process must advance to allow commercial seed companies to direct-seed in the field, Fowler said. It is simply much cheaper than producing seedlings in greenhouses and transplanting them in the field. “We’re talking about several hundred dollars difference per acre in cost compared to direct-seeding,” he said.
The first U.S. factories to produce rubber from native guayule opened in the early 1900s, but two decades of production stripped the desert of virtually all guayule, and the plants closed by the late 1920s. Meantime, the rubber industry turned to plantation-grown Brazilian Hevea rubber trees for cheaper, easier production.
During World War II federal authorities revived guayule, launching the Emergency Rubber Project, which farmed 32,000 acres of guayule at 13 sites in three states. The project was terminated at the end of the war with the renewed availability of Hevea rubber from Southeast Asia and the development of synthetic rubber.
Then in 1988, the country’s dependence on imported natural rubber once again pressed the U.S. Department of Defense into a contract with Bridgestone-Firestone to make tires from guayule at a prototype plant near Phoenix. About 1,000 pounds of rubber were reportedly produced at the pilot facility before it closed three years later.
The current hope is that the latest guayule euphoria, backed by America’s surging demand for non-allergenic latex, will put a permanent bounce into the crop’s long-term viability.
Norman Martin is a science column coordinator with NMSU's agricultural communications department. Future columns will highlight other NMSU research projects.
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