Establishment of a grafted overhead-sweetpotato cultivation system with root-function spatial division

• A grafted overhead-sweetpoato cultivation (GOSC) system has been established, and the key technique is root-function spatial division (RFSD) of sweetpotato.
• Storage roots regenerate from the scion stems buried in media and hang in the air, named overhead-sweetpotato.
• This system was suitable for all kinds of sweetpotato varieties.
• Graft compatibility, stock without underground storage roots, and nutrient-free stem-burying media, are the key factors for RFSD.

We report here a new cultivation system for sweetpotato [Ipomoea batatas (L.) Lam.] production, named grafted overhead-sweetpotato cultivation (GOSC) system. In this system, sweetpotato (as scions) was grafted with convolvulaceae relatives (as stocks), and the stems of grafted sweetpotato were buried in a solid medium without any nutrient and hung in the air to regenerate overhead-sweetpotato (storage roots). The results showed that Ipomoea trifida (6×), Beinong5521 (5×) and SH-2 (6×) were the best stocks. All the tested sweetpotato cultivars could produce overhead-sweetpotato with different yields. The mixture of sand, perlite and vermiculite with a 1:1:1 (v/v/v) ratio was the best solid medium for the GOSC system. The key stage of overhead-sweetpotato formation was about 20 days to 55 days after stem buried. Since storage roots are not regenerated from stocks grown in fertilized soil but from scion stems buried in non-fertilized solid medium, it seemed that the grafted overhead-sweetpotato plants had root-function spatial division (RFSD), i.e. absorbing roots of stocks and storage roots of scions. The graft compatibility with sweetpotato, the stock without underground storage roots, and the stem-buried media without nutrient supply, are the key factors for RFSD and overhead-sweetpotato production. This system could be used as a model for the study of the interaction between stock and scion as well as the source-sink relationship in sweetpotato.