“There are reasons to be watching this and to be concerned because regionally there will be supply challenges,” said Justin P. Gilpin, the head of the Kansas Wheat Commission. “There is uncertainty in the marketplace.”

A decade ago, the area around the Black Sea — mainly Russia, Ukraine and Kazakhstan — used to supply just about 4 percent of the wheat traded internationally. But most of the growth in demand globally has been supplied from there, and the region now produces about 30 percent of the wheat traded internationally, said Mr. Abbassian. This is the first time a supply crisis has originated from that area, he noted.

In early August, Russia announced an export ban that it would review at the end of the year, but Prime Minister Vladimir V. Putin announced Thursday that the ban on grain exports would extend into 2011. The price of wheat jumped again, and that has had a spillover effect into other grains like corn and soybeans. The forecast for the global rice harvest has also dropped, although it is still expected to be higher than in 2009 and should be a record, the F.A.O. said.

“If you look at the numbers globally, the Americans, the Europeans and the Australians can make up the supply,” Mr. Abbassian said of the wheat harvest, playing down the chances of repeating the 2008 crisis. “There is no reason for this hype, but once the psychological thing sets in it is hard to change that perception, especially if Russia keeps sending bad news.”

After two days of rioting set off by price increases for bread and utilities like electricity and water, the streets in Maputo, the capital of Mozambique, were largely calm on Friday. But 10 people had been killed and 300 injured, Health Minister Ivo Garrido told a news conference, local news agencies reported. Price increases have been much sharper in Mozambique than in most of the world because the government kept prices artificially low before elections last year, some analysts said.

As with any commodity, questions of wheat shortages spur speculation and hoarding, and experts suggest both are at play in the current market. They believe more money is washing through the commodity market for wheat because with interest rates so low and the stock market so volatile, investors are putting their money in the Chicago Board of Trade.

But the world also has to come to grips with changing weather patterns due to climate change, argued Prof. Per Pinstrup-Anderson, an expert in international agriculture at Cornell University.

“We are going to have much bigger fluctuations in weather and therefore the food supply than we had in the past, so we are going to have to learn how to cope with fluctuating food prices,” Professor Pinstrup-Anderson said.