Advancement of sweetpotato breeding for high starch content in Japan

The starch content of Japanese sweetpotato [Ipomoea batatas (L1)] cultivars is rated among the highest in the world and has been accomplished via a na tional breeding programme conducted for more than 50 years. The first step of the programme was to accumulate genes for high starch content in local c ultivars whose starch content ranged from 14 to 20%. A starch content of 15 -20% with higher storage root yield was obtained from the offsprings. Genes from foreign cultivars were then transferred to the local cultivars. Culti var 'Koganesengan' was developed from this cross producing a starch content of 22-26% and considered to be a high storage yield cultivar. Wild relativ es were also used to increase genetic variation, and 'K123' (19% starch con tent but no storage root) a hexaploid wild plant was crossed with cultivate d sweetpotato. The resulting hybrids were used to backcross(BC) with improv ed cultivars. From, the resulting BG progenies, 'Minaniyutaka' was selected and released, which had a lower starch content (19-22%) but produced more storage roots than 'Kognesengan'. Recently, 'Hi-starch' and 'Satsuma-starch ' were released. Both had the highest level of starch content 'Hi-starch' ( 28-30%) and 'Satsuma-starch' were released. Both among the cultivars releas ed in Japan.