Could This Shrub Overthrow the Mighty Rubber Tree?

Rubber can be made from the latex of several different plants, but more than 90 percent of natural rubber comes from trees. Specifically the Hevea brasiliensis trees in Southeast Asia — a fact that makes some rubber experts nervous. Growers can't easily produce enough rubber for future expected demand, and the trees are currently being threatened by both a leaf blight and climate change.

So if researchers can get a flowering shrub native to the southwestern U.S. and northern Mexico called guayule to be an alternative rubber producer, it might be a good thing. And experts are getting close, reports Cade Metz for Wired.

The world has known about this problem with rubber for years, which is part of the reason that synthetic rubber is used for a lot of toys and even passenger cars. However, high performance rubber still needs to have the natural stuff — it lasts a long time and can remain relatively cool even when its carrying heavy loads as airplane or truck tires.

Guayule uses much less water than the tropical Hevea — it’s a desert shrub after all. And guayule's greater genetic diversity means that it is less likely to be wiped out by one disease. The shrub can also be harvested by machinery, rather than painstakingly tapped by hand as the trees are, explains Jesse Emspak for Scientific American. 

Dreams of replacing Hevea with guayule aren't new. When Japan captured Singapore in February 1942, the United States and allies lost access to 95 percent of their rubber supply. The Emergency Rubber Project, based in Salinas, California, launched a massive effort to find a better source for natural rubber. Part of the quest included putting Japanese Americans interned at the Manzanar camp in California to work. For Chemical Heritage Magazine, Mark R. Finlay writes:

Robert A. Emerson, an expert on photosynthesis, as well as a Quaker, pacifist, and social democrat, is at the center of much of this story. Based at the California Institute of Technology, Emerson was convinced that the internment policy was "an organized effort to reduce the Japanese to slavery." The internees included many skilled chemists, botanists, plant physiologists, and nurserymen, and Emerson came to believe that science—specifically, producing rubber from guayule—would demonstrate that many of the Japanese Americans were "more than willing" to serve their country and contribute to the nation’s defense.

Both Ansel Adams and Dorothea Lange took pictures of the internees cultivating guayale plants in the arid valley. Unfortunately, prejudice against Japanese Americans ran strong. Finlay writes that leading natural-rubber expert of the time, David Spence, "described the Manzanar scientists’ methodologies as 'exceedingly interesting,' yet he did not want to get 'mixed up' in anything that aided" the Japanese. After Japanese Americans were released from the camps, the guayule production dried up. Still, the discoveries the internees made on cultivation of the shrub and extraction of its sap continue to inform today’s guayule efforts.

But each plant yields only a small amount of rubber, Metz writes for Wired. So researchers today are turning to advanced genetic techniques to help guayule fulfill its potential. By the end of the year scientists should have the plant’s complete genome, including the genes that determine its size, shape and number of latex-oozing cells it grows. Metz reports:

The potential for improvement is enormous — in part because guayule is so under-bred, in part because breeding technology is evolving so quickly. "The creation of a guayule commodity, which is what we’re all banking on here, is behind the science. That’s almost never the case," says [USDA researchers Colleen] McMahan. "We knew a whole lot about how great humans evolved before we ever sequenced the genome. We know so much less about how to breed guayule. But we're now going to get all this information about how it works."

A company called the Yulex Corporation is also working to breed hybrid guayule plants that combine the best traits of several different strains. Company researcher Eric Mathur says that their best hybrid is a superplant that can produce a metric ton of rubber per acre of guayule. Getting farmers to grow enough guayule still remains a challenge, and how quickly that can happen is still uncertain.

But if Yulex, Mathur and other scientists succeed, guayule may be a big source of American-made natural rubber in just a few years.

Maris Fessenden | | READ MORE

Maris Fessenden is a freelance science writer and artist who appreciates small things and wide open spaces.