Tuberous root growth and antioxidant contents of 2 sweetpotato (Ipomoea batatas (L.) Lam.) cultivars were examined using 2 different irrigation schemes: surface-irrigation and subirrigation. Coarse silica sand was used for root media, which maintained well the gas permeability and water drainage around the roots. The root surface was periodically wetted for watering in the surface-irrigated roots, while the sub-irrigated roots were not. The irrigation methods did not affect the oxygen concentration around the roots. No differences in plant growth were observed between the 2 irrigation methods. However, the content of α-tocopherol in the tuberous root was significantly higher in the ordinary-irrigated roots for both of two cultivars. Thus, the periodical wetting increased the α-tocopherol content in the tuberous root of sweetpotato cultivars without any apparent changes in tuberous root development.
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