This just in: Detroit's got another challenge from Japan, and this one's deep in the heart of Texas.

Down in San Antonio, Toyota Motor's (NYSE:TM) newest U.S. factory, informally dubbed the "Triple-T" (for Toyota Tundra Texas) Ranch, went on line on Friday, rolling out a pair of brand-spanking new 2007 Tundras -- a number expected to swell 100,000-fold over the next year. Incidentally, that 200,000 trucks-per-year capacity is already up by a third since the San Antonio plant was first announced three years ago, and local business leaders are hoping Toyota will agree to double the plant's size again if things go well.

And how well is "well"? Well, Toyota looks likely to close out this year with about 100,000 Tundra sales in the U.S., and hopes to increase that to 200,000 next year. If met, that goal suggests that no sooner will the San Antonio plant reach full production than the company would need to expand it, or build more plants, to satisfy anticipated demand.

So it's little wonder that management calls the "full-size pickup truck market . by far, the single-largest opportunity for Toyota's future growth plans in the U.S." For all the success of the company's headline-grabbing Prius and other hybrid vehicles, which continue to run circles around the hybrid offerings of GM (NYSE:GM) and Ford (NYSE:F) (and Honda (NYSE:HMC)), Toyota still sells fewer hybrids here than it does pickups. Now it turns out the pickup market is the faster-growing one.

The corollary to that, of course, is that Toyota has put Detroit on the defensive once again. No sooner have GM, Ford, and -- finally -- DaimlerChrysler (NYSE:DCX) decided they need to develop hybrids to satisfy the market that Toyota and Honda created than Toyota is challenging them on their own turf: the profitable market for full-size pickups (in which the Detroit Big Three hold a 90% market share). The fact that Toyota has chosen to plant its flag, and its Tundra factory, deep in the heart of Texas just adds insult to the injury.

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Fool contributor Rich Smith does not own shares of any company named above.