LONDON—A global food crisis sparked by Russia’s invasion of Ukraine escalated on Wednesday as Indonesia tightened curbs on palm oil exports, adding to a growing list of key producing countries seeking to keep vital food supplies within their borders. The conflict in Ukraine is threatening global grain production, the supply of edible oils and fertilizer exports, sending basic commodity prices rocketing and mirroring the crisis in energy markets. Palm oil is the world’s most widely used vegetable oil and is used in the manufacture of many products including biscuits, margarine, laundry detergents, and chocolate. Palm oil prices have risen by more than 50 percent this year. Indonesia’s Trade Minister Muhammad Lufti said the export curbs aimed to ensure that cooking oil prices at home remain affordable to consumers. The rise in prices comes at a time when the affordability of food is a major challenge as economies seek to recover …