Germany and Japan, two of the world's biggest exporters, cast doubt over the strength of economic recovery on Thursday, adding to concern that nascent growth may disappear without sustained government stimulus. The two economic heavyweights, along with France and Hong Kong, have pulled out of a recession, spurring markets to rise and governments to consider winding down stimulus programmes. But talk of exiting from measures triggered by the worst financial crisis since the 1930s is being overtaken by words of caution on the rebound's strength before a G20 leaders summit in Pittsburgh to discuss finanial reform next month.