Guayule

Scientific Name(S): Parthenium argentatum A. Gray Family: Asteraceae

Common Name(S): Guayule (pronounced "why-oo-lay")

Botany: Guayule is common shrub native to the Chihuahuan desert of northern Mexico and the adjacent Big Bend region of Texas. The plant can be readily grown in the arid regions of the southwestern US.

History: Guayule had a history as a domestic source of rubber. In the early 1900s, guayule accounted for almost 50% of all the natural rubber consumed in the US and 10% of consumption worldwide. A variety of factors, including the Great Depression and the Mexican Revolution, combined to destroy the industry. The US mounted an intensive research program under the Emergency Rubber Project to identify a domestic source of natural rubber as supplies from Southeast Asia dwindled because of World War II. The work led to the re-evaluation of guayule. The project was ended after the war, following the development of synthetic rubber and the return of cheap Hevea rubber. In 1977, interest in guayule was renewed when the National Research Council noted that the increasing demand for imported natural rubber could result in domestic shortages. The escalating price and variable supply of foreign petroleum, along with the great advantage that guayule can be harvested mechanically, made guayule rubber production attractive from both economic and national security standpoints.

Uses of Guayule

Guayale is used in the production of rubber. Its use as a fuel is being investigated.

Side Effects of Guayule

Contact with Guayule can cause strong erythema. The potency of its allergen (guayulin A) has been equated to that of poison ivy.

Toxicology: Guayule contains a potent contact allergen, long known to pose a hazard to guayule farmers and processing-plant employees. More recent investigations of acetone extracts resulted in the isolation of guayulin-A, a potent elicitor of contact dermatitis. This sesquiterpene cinnamic acid ester induces strong erythema in animals within 24 hours of application in concentrations as low as 0.003% (0.5 nM), which persists for almost 2 weeks. The compound is present in stems and leaves at levels of 0.05% to 0.3%. Guayule processing plants are now designed to minimize worker contact with resins. The allergenicity of guayulin-A may cause unexpected difficulties in the cross-breeding of Parthenium species to develop high-yield strains. Guayule readily undergoes hybridization with mariola and P. to­mentosum var. stramonium, close desert relatives. These species contain sesquiterpene lactones that are cytotoxic and produce skin reactions in persons sensitized to other species of Asteraceae. Preliminary investigations of crosses of P. tomentosum with guayule indicate the presence of guayulin-A and stramonin-B (a cytotoxic pseudoguaianolide) in the first generation of experimental hybrids.

Summary: Guayule is slowly becoming an economically important rubber substitute, although its commercial development has not been as rapid as once hoped. Its more widespread cultivation may result in an increased incidence of allergic dermatitis among guayule farmers.

Guayule rubber plant is made up of a cispolyisoprene core. The sesquiterpenes guayulin C and D have been described.