The announcement from McDonald's follows a Reuters report that Beyond Meat rival Impossible Foods is no longer trying to win a deal with McDonald's because it cannot produce enough of its imitation meat to partner with the world's biggest fast food chain.

Beyond Meat shares, which closed up 12.5% on Tuesday after the news, rose another 5% after the burger chain's statement on the trials.

McDonald's late last year was one of the last big fast-food chains to announce tryouts of a plant-based sandwich in 28 restaurants in southwestern Ontario. The expanded trials will now cover 52 outlets and last another three months.

Since then, analysts and industry consultants have questioned whether the popularity of the plant-based meat burgers will prove sustainable and large enough to justify a wider U.S. launch.

McDonald's said on Wednesday that in the new trials, the vegan burgers would be 50 Canadian cents cheaper at C$5.99 (3.51 pounds), but added the price would vary by outlet.

A report from the Canadian business newspaper Financial Post, citing a company executive, said the change in price did not have to do with customer feedback, but to see how the change would influence demand. (https://bit.ly/2T2QQG5)

McDonald's in its statement did not indicate the level of demand or customer interest it was getting from the initial tests.

UBS said in December McDonald's could sell more than 250 million Beyond Meat P.L.T. burgers annually if it rolled out the product across its nearly 14,000 U.S. outlets, based on the Swiss investment bank's tests that showed McDonald's was selling nearly 100 burgers a day at some Canadian outlets.

"As we expand the test, we're continuing to listen to our guests ... and assess the appetite for a plant-based alternative," Michaela Charette, head of consumer insights at McDonald's Canada, said in the statement on Wednesday.

(Reporting by Praveen Paramasivam in Bengaluru; Editing by Shinjini Ganguli and Maju Samuel)