Nissan Motor Co. Ltd. and Chrysler Group LLC say they have agreed to end three pacts announced last year, one of which included Chrysler supplying Nissan with a fullsize pickup truck for the U.S.

“For the past several months, teams from both companies have been studying the viability of the projects in light of significant changes in business conditions since the projects were announced in January and April of 2008,” Nissan says in a statement. “Today it was decided it was in the best interests of both companies to end the projects.”

Chrysler in 2011 was to build a version of the Dodge Ram to replace Nissan’s own in-house Titan large truck. It was expected Nissan also would have received Chrysler’s Hemi engine technology.

Nissan officials have said they want to remain in the fullsize truck segment and spokesman Fred Standish says Nissan has “lots of time” to decide how to do so. Nissan, as previously planned, will continue to build the Titan through model year ’10, into 2011.

When it became clear in the spring the project might not move forward, due to Chrysler’s bankruptcy filing, Nissan’s chief U.S. product planner, Larry Dominique, told Ward’s Nissan was contemplating how to upgrade the current Titan.

He since reportedly has suggested Nissan would look for a new partner to build a next-generation fullsize pickup.

Two other projects the auto makers were to collaborate on was a Nissan-inspired subcompact car that Chrysler would sell in South America, and a Chrysler-designed/Nissan-manufactured small car for global markets in 2010.

Standish says the South American program was originally to begin in June or July of 2009.

However, sources tell Ward’s development of the global car had reached advanced stages. It was to be based on the Dodge Hornet concept unveiled at the 2006 Geneva Motor Show.

As Chrysler’s alliance with Fiat Auto SpA evolved, former Chrysler product guru Frank Klegon suggested to Ward’s the auto maker might market two small cars – the Hornet and a Fiat-inspired design.

Following Chrysler’s emergence from bankruptcy in June, Fiat acquired a 20% stake in the auto maker. In return, Fiat will supply Chrysler with platforms and engines to market small cars.