Rubber from lettuce, a non sequitur if there ever was one, is the topic of study for Washington State University scientists who say a weed called prickly lettuce could provide raw material for rubber production.

Ian Burke, an associate professor at WSU’s department of soil and crop sciences in Pullman who calls himself a weed scientist, says findings from the study indicate the weed could become a cash crop source of natural rubber grown in Eastern Washington.

Prickly lettuce, a wild relative of cultivated lettuce, has a milky white sap that bleeds from its stems, producing a rubber substance after it hardens, Burke says, adding that the milky sap of the plant could be used to produce rubber.

“The best part is that it’s very common. It’s everywhere on every continent where plants grow,” Burke says.  “Prickly lettuce is edible, and it’s one of the bitter herbs mentioned in the Bible.”

He adds, “Domesticated lettuce is very closely related to this prickly lettuce, but when it was domesticated, it was selected for lettuce that doesn’t have much latex because it doesn’t taste good.”

Almost all of natural rubber is extracted from rubber trees grown in Africa and Southeast Asia, he says.

“But those trees are susceptible to disease. Natural rubber demand has done nothing but increase over the years,” Burke says. 

Natural rubber is the main ingredient for everyday products such as boots, condoms, and surgical gloves, as well as tires. Roughly 70 percent of the global supply of rubber is used in tires. Burke says more than 50 percent of rubber products are made from synthetic rubber, which is made using petrochemicals and can be stronger in some cases than natural rubber. Synthetic rubber is also used in tires, hoses, door casings and flooring. 

Burke says Jared Bell, a WSU doctoral student, and Michael Neff, a molecular plant scientist, began studying the weed with two distinct samples from Eastern Washington. The scientists were able to identify genetic markers for rubber content, which Burke says makes it easier to select for certain traits, such as early bolting plants with multiple stems, which would allow for more than one harvest in a season.Bolting occurs when agricultural and horticultural crops prematurely produce a flowering stem—or multiple stems—before the crop is harvested, in a natural attempt to produce seeds and reproduce. 

“We have genetic markers for quality and quantity, which is part of the recipe for improving traits in a plant,” he says. He adds that other traits, such as efficient use of water, would enable prickly lettuce crops to be grown with minimal rainfall. It also could be grown in rotation with other crops. 

Burke says the study is one of the first steps to determine whether there’s enough variability in prickly lettuce before scientists go on to study a breeding system to improve it. 

“Prickly lettuce plants are all variable in length. That’s a problem we need to overcome, and the next step would be to select for increased rubber particle size and uniformity. The fact that we already have variability is important because we can select for improvement,” he says. 

He says it could be a long, 10-plus years before any production system could be developed, but he feels that the research has introduced the promise of a source of rubber in the future.

“Crops for rubber production would be a wild guess on my part, but we’ve opened the front door,” Burke says.

He says Jared Bell, the graduate student who worked on the study, is an “exceptional young man who was interested in the quality and quantity of prickly lettuce in Eastern Washington.” 

Burke says he’s waiting for another graduate student to help with the work, and says there has been quite a bit of interest in the research. 

The study was funded in part by a special U.S. Department of Agriculture grant. The study was published recently in the Journal of Agricultural and Food Chemistry, which described the plant’s genetic code linked to rubber production.