LIMBURGERHOF, GERMANY — BASF and Monsanto Co., St. Louis, have agreed to expand their collaboration to develop higher-yielding and stress-tolerant crops to include a fifth crop: wheat. The companies said they will increase their investments in the collaboration, which was established in 2007 and already includes corn, soy, cotton and canola.

By adding wheat to the collaboration, the companies expect to invest an additional $1 billion on top of the $1.5 billion joint budget the companies dedicated to the original effort.

“Our yield and stress collaboration with BASF already has brought forth so many promising leads, the first of which we’ll see on farm in coming years with our first-generation drought-tolerant corn,” said Robb Fraley, chief technology officer for Monsanto.

Peter Eckes, president of BASF Plant Science, added, “The expansion of our partnership reflects the fit between the two companies. The yield increases that we have achieved together in the field so far give us confidence that we can do more in our collaboration crops, which now include wheat.”

The companies said they will continue to operate under the terms of their original collaboration, with each company maintaining independent trait discovery programs, nominating from those programs specific candidate genes to advance for accelerated joint development. Projects will be funded jointly through each phase of development, and Monsanto will commercialize products that emerge from the joint development. The two companies will share the profits associated with commercialized products. Monsanto will receive 60% of net profit, and BASF will receive 40%.

As part of their collaboration on wheat, BASF and Monsanto initially will focus on developing biotech products for the North American and Australian markets. The first enhanced yielding wheat product is expected to reach the market after 2020, the companies said, to be followed by successive generations of higher-yielding wheat varieties.

The companies expect to introduce the world’s first bioengineered drought-tolerant corn about 2012, pending regulatory approvals. Drought-tolerant corn, the first product emerging from the companies’ joint pipeline, is designed to provide farmers yield stability during periods of low rainfall by mitigating the effects of water scarcity on corn plants. Field trials for drought-tolerant corn conducted in the Western Great Plains met or exceeded the target yield enhancement — an increase of roughly 7 to 10 bus per acre over the average yield of 70 to 130 bus per acre in some of the key drought-prone areas in the United States.