As yaki-imo became a staple winter food for low-income areas, sweet potato specialty stores and vendors boomed in the early 20th Century. But in 1942, the wartime Staple Food Control Act rationed the sale of various foods, including rice and sweet potatoes, and many sweet potato shops were closed. Nevertheless, they became a key staple during World War Two, when crops like wheat and barley were even scarcer. "Sweet potato flour was used as a substitute for wheat flour," Rath explained. "From 1944, public lands were converted into potato patches, and sweet potatoes would replace the meagre rice allotments in public rations by 1945."