PULLMAN, Wash.—Plant scientists have identified as many as 2,500 plants that produce at least some amount of natural rubber latex.
However, only the rubber from the Heveatree has ever been widely used commercially, although the desert shrub guayule and the Russian dandelion, or Taraxacum kok-saghyz, seem on the verge of a commercial breakthrough.
Nevertheless, plant scientists at Washington State University and Dow Agrosciences have found a fourth candidate as a cash crop for rubber—a common weed that is a cousin to the green leaves you find in your salad.
Prickly lettuce (lactuca serriola), a weed widely found in Eastern Washington, synthesizes long-chain natural rubber, according to a study published in December 2014 in the Journal of Agricultural and Food Chemistry.
Scientists Ian C. Burke and Michael M. Neff of WSU and Jared L. Bell of Dow performed genotypic and phenotypic analyses on prickly lettuce, leading to the discovery of genetic regions linked to natural rubber production, according to the abstract on the journal's website.
“Prickly lettuce is an excellent candidate for elucidating the rubber synthetic mechanism and has potential as a crop plant for rubber production,” the abstract said.
Burke, an associate professor of weed science at WSU, is enthusiastic about prickly lettuce.
“I think there's interest in developing a temperate-climate source of natural rubber,” he said. “It would be really great if prickly lettuce could become one of those crops.”
In terms of quality, the latex from prickly lettuce is similar to that from the Russian dandelion, according to Burke.
“Polydispersity is much higher (in prickly lettuce latex), but our article documents genetic variation among haplotypes/biotypes, indicating that there could be improvement—minimization of polydispersity—through breeding,” he said. “Prickly lettuce rubber and latex are also hypoallergenic,” he said.
However, the quantity of rubber that can be obtained from prickly lettuce is still a question mark, Burke said.
“It's currently a challenge to harvest and extract on a whole plant basis, and we are stuck milking plants,” he said. “That's a laborious and time-consuming process.”
Prickly lettuce is an herbaceous annual, and rubber content in its sap ranges from 2.5 to 5 percent, Burke said. The plant will grow to a height of 6 to 8 feet in two months, he said.
“And that's here in Pullman, Wash., which is virtually a desert,” he said. Prickly lettuce is remarkably drought-resistant, he said.
Burke said he couldn't readily answer questions about the commercial potential of prickly lettuce, because he is not a rubber crop specialist. But he is optimistic.
“There will have to be an investment in breeding for traits that facilitate rubber production,” he said. “That's not easy or fast. We need to determine the production potential on an area basis, and we need to think about where and when we could produce this crop. We aren't likely to see prickly lettuce as a rubber crop soon.”
While work continues on prickly lettuce, it isn't the kind of work that would lead the plant quickly toward commercial viability, according to Burke.
“I have a working relationship with a rubber company, but it hasn't advanced to a funding relationship yet,” he said.