Extremely Early Flowering and Large Grain Isogenic Japonica Rice Koshihikari Integrated with Gene e1 and GW2

Abstract The extremely early flowering/large-grain isogenic Koshihikari was developed by combining the large-grain allele, GW2, derived from Inochinoichi with the year-round flowering allele, e1, from Kanto 79. We conducted four back crosses with Koshihikari as a recurrent parent by using an extremely early flowering/large-grain e1GW2 homozygote as a non-recurrent parent, which was segregated in B1F2 between Kanto 79 and a large-grain fixed F3 plant in Koshihikari × Inochinoichi. In the BC4F2 population, the e1GW2 homozygous phenotype was selected and fixed in BC4F3 as Kshihikari e1GW2. plants were segregated according to a ratio of 1 extremely early flowering/large-grain e1GW2 : 3 extremely early maturing/small-grain e1gw2 : 3 medium-maturing/large-grain e1GW2 : 9 medium-flowering/small-grain E1gw2 and e1GW2 homozygous isogenic Koshihikari [Koshihiakri e1GW2] was fixed in BC4F3. Whole genome sequencing of Koshihiakri e1GW2 proved that already known 1 deletion in GW2 at 8,147,416 bp on chromosome 2, and an e1 isogenic-specific SNP at 9,090,618 bp, which was 35,213 bp downstream to the 3□ side of Ghd7 on chromosome 7. RT-qPCR analyses showed that the transcription of Ghd7 was suppressed in Koshihikari e1GW2 than in Koshihikari. The Koshihikari e1GW2 flowered 14 days earlier than Koshihikari and thousand grain weight of Koshihikari e1GW2 (27.8 g) was 18% larger than Koshihikari (23.6 g). We successfully integrated GW2 with e1 for the first time, especially in the genome of a globally produced Japonica leading cultivar Koshihikari. The Koshihikari e1GW2 was registered under plant varietal protection. Competing Interest Statement The authors have declared no competing interest.