By David Lawder WASHINGTON (Reuters) -The Ukraine war’s disruptions to grain and fertilizer flows have prompted the worst food security crisis since at least the one following the 2007-2008 global financial meltdown, with some 345 million people now facing life-threatening shortages, the International Monetary Fund said on Friday. A new IMF research paper estimates that the 48 countries most exposed to food shortages face a combined increase in their import bills of $9 billion in 2022 and 2023 due to the sudden jump in food and fertilizer prices caused by Russia’s invasion. This will erode res…