Introgression of Green Revolution sd1 gene into isogenic genome of rice super cultivar Koshihikari to create novel semidwarf cultivar ‘Hikarishinseiki’ (Koshihikari-sd1)

The rice super cultivar ‘Koshihikari’, grown on 37% of the total rice area in Japan, has been a leading cultivar since 1979. It is also grown in the USA and Australia. However, its tendency to lodge makes harvest difficult and reduces grain quality, and the regularity of large-scale typhoons compromises its production nationally. The genetic improvement of Koshihikari against lodging has been an extremely important theme for the past 30 years in Japan. This paper describes the development of a semidwarf form of Koshihikari by the fixing of an allele of the Green Revolution semidwarf gene sd1 via eight recurrent backcrosses. The cultivar, with excellent flavor and high yield, was named ‘Hikarishinseiki’, which means “Bright New Century” (rice cultivar No. 12273; Ministry of Agriculture, Forestry and Fisheries of Japan: MAFF). Hikarishinseiki, with ≥99.8% of the Koshihikari genome, is about 20 cm shorter than Koshihikari. DNA monitoring of Hikarishinseiki confirmed its genomic substitution into Koshihikari except for sd1 and a marker-based method to distinguish Koshihikari from Hikarishinseiki was developed. Its flavor (upper medium grade) and quality were the same as those of Koshihikari grown at 10 sites across Japan, but its yield was on average 3% higher (maximum 29% higher at Hyogo) than that of Koshihikari and it was highly resistant to lodging. Hikarishinseiki is the first semidwarf form of Koshihikari registered by MAFF. Some economical impact has been achieved by introducing Hikarishinseiki and it is already notified as a brand rice description in the rice-producing districts of Niigata, Shiga, Tottori, Okayama, Tokushima, and Kochi prefectures.