Call it the jatropha bubble. When word got out several years ago about the promise of a small subtropical tree called jatropha, it became a biofuel sensation. Advocates claimed the fruit tree was hearty, drought-resistant and could be grown on marginal land. Its oil seeds offered a promising biofuel that wouldn’t compete with food crops. Air Japan, Continental Airlines and Air New Zealand ran test flights of planes using jatropha-based biofuel, prompting more than 100 companies to plunk down millions on jatropha plantations in developing countries. Energy giant BP (BP) sunk $160 million into the farms, and one industry group projected that $1 billion would be invested annually in jatropha. Then everything crashed. Jatropha, it turned out, was much harder to grow than once thought. Yields were inconsistent, and many farmers didn’t have the training needed to manage commercial-scale crops. Most of the jatropha operations shut down.