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The rice cultivar Hikarishinseiki, a semidwarf isogenotype of Koshihikari carrying the Green Revolution sd1 gene, is increasingly grown in both Japan and the United States. Here, we report DNA diagnosis for Hikarishinseiki targeting its Jukkoku-type sd1 locus, which codes for a defective gibberellin 20-oxidase, with a 1 bp substitution in exon 1 (Jukkoku-type GA20ox- 2 mutant allele: Jukkoku_ GA20ox- 2). An allele-specific primer (ASP)-polymerase chain reaction (PCR) with primers SD1F3 and SD1JR gave a PCR product specific to Jukkoku_ GA20ox- 2. In addition, ASP-PCR with primers SD1F3 and SD1NRM (which contains a mismatch at the third nucleotide from the 3′-terminus of SD1NR) gave a PCR product specific to non- Jukkoku_ GA20ox- 2. Multiplex ASP-PCR using SD1F3, VIC dye-labeled SD1JR, and FAM dye-labeled SD1NRM enabled simultaneous codominant detection of Jukkoku_ GA20ox- 2 and non- Jukkoku_ GA20ox- 2 among 188 cultivars. Also, Hikarishinseiki is identifiable by RM253 polymorphism from 11 cultivars carrying Jukkoku_ GA20ox- 2. Taken together, our results establish a methodology for distinguishing Hikarishinseiki. [ABSTRACT FROM AUTHOR]

Abstract: 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 20cm 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. [Copyright &y& Elsevier]