The California Prune Board is running activities for Sport Relief, including school fundraising activity and a sampling campaign at 250 Sainsbury's Sport Relief Miles.
"Prunes are a spontaneous purchase item and positioning in store is vital," said California Prunes European marketing director Mark Dorman. "We are trying to reposition the prune as a snack item rather than an additive."
Sales had been growing steadily until the start of the global downturn but then stagnated, said Dorman.
Half the world's prune supply is from the US state, with Argentina, Chile and France the other major producers. California's share of the £14.3m UK market fell from 60% to 45% last year as buyers sought out cheaper South American fruit.