In Japan, sweetpotato (Ipomoea batatas (L.) Lam.) is consumed not only as a food but also as a raw material of starch industry. However, the use of sweetpotato as starch decreased drastically in the 1960s and 1970s, when other starches, such as corn or cassava, were imported. Sweetpotato production in Japan had been about 400,000 ha in 1960, but it has decreased by one-tenth in the last 40 years. During this time, research into starch accumulation in sweetpotato has also changed. At first, sweetpotato researchers concentrated on reducing the cost of starch production by increasing the starch yield. They were interested in the quantitative issue of starch accumulation in storage roots. After the Uruguay Round Agreement, sweetpotato starch research centered on the quality of starch in Japan. Efforts were made to modify the properties of sweetpotato starch to overwhelm the foreign competition. The physiology of starch accumulation is reviewed in this paper from the viewpoint of the sink-and-source relationship. The primary focus is on the quantity of starch. In addition, recent results from breeding experiments designed for improving the quality of starch in sweetpotato are introduced.
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