John concedes that commercial applications will probably require boosting PHB levels by three times or more, which may take years. In the meantime, the company plans to stick other useful polymers inside cotton fibers. Genetic engineering may not be necessary to grow improved materials, however. The plant naturally produces latex-although not nearly as profusely as the tropical trees from which all rubber products currently ow. But 15 years of classical breeding has tripled its rubber output to about 900 pounds per acre-comparable to tropical trees, says breeder Dennis Ray of the University of Arizona.
Guayule rubber is as durable and strong as tropical rubber, and it has two advantages.
It grows in such arid regions as Arizona, where tropical trees cannot. More important, guayule rubber is nonallergenic. This property, says Katrina Cornish of the U.S. Department of Agriculture, is what gives guayule its niche. There are 57 allergenic proteins in tropical rubber. As a result, latex allergy, with symptoms ranging from simple skin irritation to anaphylactic shock, is common among health care workers and others who frequently come in contact with rubber.