Mutation breeding of sweet potato by gamma-ray radiation

This gamma irradiation study was conducted to produce sweet potato mutants having high yield and high starch content. Regenerated plants from gamma-irradiated stems were grown in the field. Twentynine plant lines were selected by estimating storage root size, shape and yield. Genetic variation and phylogenetic relationship among the lines were investigated assuming the specific traits. Also, the flowering of sweet potato should be artificially induced by grafting and short-day treatment in northeast regions of Asia, such as Korea and Japan (Ahn et al., 2002). Furthermore, the self- and crossincompatibility of this crop limits the use of genetic resources, and it is very difficult to breed new varieties and improve varieties through cross breeding (Ahn et al., 2002; Martin, 1965). Mutation breeding can be used as a major approach in improving sweet potato varieties, since it is a clonally propagated crop. Irradiation-induced mutation breeding is effective in improving sweet potato characters such as yield, starch and soluble sugar content, carotenoids content of storage roots and disease resistance (Kukimura, 1986; Wang et al., 2007). Irradiation has also been successfully used for mutation breeding in various crops and ornamental plants (Song and Kang, 2003) and has proven an adept means of encouraging the expression of recessive genes and producing new genetic variations (Schum, 2003; Song and Kang, 2003; Yoon et al., 1990). Sweet potato is a typical starch crop that is used as a foodstuff and, importantly, for industrial applications. In the present study, gamma irradiationmediated mutation breeding was applied to sweet potato to produce useful varieties having a high yield and high starch content. Irradiation-induced mutants were grown in the field and assessed for their starch and sugar characteristics.