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For Bridgestone, the backup plan is a desert shrub

Bridgestone is growing guayule in the U.S. state of Arizona.

TOKYO -- It's happened before and it can happen again. Bridgestone knows it can ill afford a devastation of the rubber trees of Southeast Asia, as happened a century ago in South America. That is why the world's largest tire maker is working to diversify its sources of natural rubber by developing the means to cultivate and utilize a completely different kind of plant.

The skies are usually clear in Eloy, Arizona, and the summers are so hot and dry that hiking without water is a recipe for dehydration. But the guayule plant thrives in such conditions, and that is why Bridgestone has a research farm there with 114 hectares of guayule under cultivation.

Guayule is a flowering shrub in the daisylike aster family that grows naturally in the arid climates in North and Central America, Australia and the Mediterranean region.

The shrub produces a kind of natural rubber with qualities rivaling the rubber from the Para rubber trees grown on plantations in Southeast Asia. It takes three years from cultivation to harvest.

Bridgestone made its first passenger tires using 100% guayule rubber in October 2015. It hopes to have the bugs worked out and a system in place by the first half of the 2020s to manufacture tires on a commercial scale.

The company transports the harvested guayule plants from Eloy to its Biorubber Process Research Center in nearby Mesa, Arizona, where the natural latex rubber is extracted from the plants.

The rubber used to make passenger-vehicle tires is split evenly between natural rubber and petroleum-derived synthetic rubber. But giant tires like those for construction machinery are all made from 100% natural rubber, because of its excellent durability.

For industrial applications, natural rubber is extracted from the Para rubber tree, and nearly all of these trees are grown on plantations in Southeast Asia. Bridgestone itself cultivates Para rubber trees on a combined 24,000 hectares in two locations in Indonesia, supplying nearly 10% of its own demand for tire rubber.

There was a time when Brazil and other parts of South America were production regions for Para rubber trees. But during the 1900s, a plant disease called South American leaf blight, or SALB, raged through Brazil, devastating the rubber crop and virtually ending production there.

There is a real possibility that SALB could once again raise its ugly head in Southeast Asia, and the worries are so high in the main production region of Indonesia that the airport in Medan, in North Sumatra, has posters warning about SALB epidemics.

But SALB is not the only worry -- Para rubber trees are also prone to frequent outbreaks of a plant disease called white root rot.

"It is estimated that around 10% of the crop is lost every year," noted Norie Watanabe, a senior research fellow at Bridgestone's Central Research.

Bridgestone is scrambling to devise countermeasures, for example by harnessing biotechnology to establish a way to diagnose white root rot, but the war against disease damage is never-ending.

Rocks in the road

Although guayule is a promising alternative source of natural rubber, two hurdles need to be jumped before the bush can be put to commercial use this way.

First, the yields must be increased. Whereas Para rubber trees produce 1.5-2 tons of rubber per hectare, with the guayule bush "you cannot get even half that," Watanabe said.

In Arizona, Bridgestone is progressing with the selective cultivation of guayule seeds to get yields as high as those of Para rubber trees.

But there is also a technical challenge. "The process of extracting rubber from the guayule plant is complicated," explained Toshihiro Uchiyama in the natural rubber research unit of the company's Central Research.

To use guayule, it needs to be finely chopped up, the rubber component extracted, the woody component removed, and the resin component isolated.

That is a far cry from simply tapping a Para rubber tree and letting the latex rubber seep out.

Improvements like temperature control need to be made in every step of the process.

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