No joke: crop scientists are developing rubber lettuce

Every year, more than 20 million metric tons of rubber are fashioned into products ranging from car tires to condoms, and these indispensables of modern life come at a heavy environmental cost. More than half of rubber is synthetic, derived from petroleum, while natural rubber comes from an Amazonian tree, Hevea brasiliensis, that is cultivated on plantations throughout the tropics.

One recent study found that rubber is the fastest-growing tree crop in Southeast Asia and soon will likely pose as much threat to rainforest species like orangutans as palm-oil plantations do.

But now, a team of researchers from Washington State University has taken the first steps to developing a new source of rubber and turning a troublesome weed into a cash crop. The research is part of a larger effort funded by the U.S. Department of Agriculture to develop products and biofuels from weedy plants.

The weed, called prickly lettuce (Lactuca serriola), is a bane of vacant lots and wheat farmers alike. It’s a close relative, and thought to be the wild ancestor, of edible garden lettuce (Lactuca sativa). But one look at the spines running along the edge and down the center of its leaves and you know you wouldn’t want prickly lettuce in your salad bowl.

It might make a good pair of rubber-coated tongs for tossing that salad, though. When lettuce plants flower, or bolt, they send up tall stems full of a milky sap. And the sap of prickly lettuce happens to contain compounds that are remarkably similar to natural latex, even though the plant is not closely related to a rubber tree at all.

In the new study, the researchers analyzed the genomes of prickly lettuce specimens collected from fields in eastern Washington State. They identified genetic markers linked to early bolting, production of multiple stems, and latex chemistry, they reported last month in the Journal of Agricultural and Food Chemistry.

Gardeners want lettuce that produces lots of leaves, holds off on flowering, and contains little sap (which after all isn’t very appetizing). But rubber manufacturers want the opposite sort of plant. “Bolt early and often” would be the motto of rubber-producing prickly lettuce: a plant that sends up a latex-containing stem early in the growing season and produces multiple side stems would enable farmers to harvest latex several times from the same plant.

By providing clues about the genetics behind these characteristics, the study’s findings could help scientists breed prickly lettuce with existing cultivated lettuce varieties to produce a “rubber lettuce” crop.

Such a crop would mean that rubber could be produced in temperate as well as tropical regions, perhaps as a low-maintenance cover crop planted when fields are fallow. And eventually, that rubber lettuce might take some of the pressure off of Southeast Asian rainforests, enabling orangutans and other rainforest species to turn over a new leaf. – Sarah DeWeerdt | 12 May 2015

Source: Bell J.L. et al. 2015 Genetic and biochemical evaluation of natural rubber from eastern Washington prickly lettuce (Lactuca serriola L.). Journal of Agricultural and Food Chemistry DOI: 10.1021/jf503934v

Header image: A prickly lettuce (Lactuca serriola) leaf. Credit: Harry Rose via Flickr.