Production of a useful mutant by chronic irradiation in sweetpotato

Sweetpotato cultivar Kokei No. 14 was planted in a ⁶⁰Co gamma field. Shoot apices from the plants irradiated with different doses were cultured on MS medium supplemented with 2.0 mg/l 2,4-D for the induction of embryogenic calluses and the formation of somatic embryos. Embryogenic calluses with somatic embryos were transferred to MS medium supplemented with 1.0 mg/l ABA to induce the germination of somatic embryos. Plantlets from somatic embryos developed into whole plants on the basal MS medium. The regenerated plants were transplanted in a field and from them one mutant with alteration of root flesh color and yield was obtained. The root flesh color had changed from light-yellow in the wild-type plant into orange in the mutant. The yield of storage roots increased significantly from 218.8 ± 60 g (FW) in the original plant to 646.9 ± 150 g (FW) in the mutant per plant. Carotenoids content of the storage roots in the mutant had significant difference compared to the wild-type at the 1% level. Peroxidase isozymes and RAPD polymorphism were also analyzed between the mutant and the wild-type plants.