The coronavirus outbreak has sparked one of the largest retreats in commodity prices in years, forcing investors to brace for even steeper declines and sending a warning signal about the world economy’s prospects in 2020.

Raw materials sensitive to shifts in global growth have been among the hardest hit investments since the coronavirus began spreading around the globe and hurting travel and corporate activity. Oil prices have fallen 32% in less than two months and last week recorded their worst week since the financial crisis....