Combining two semidwarfing genesd60andsd1for reduced height in ‘Minihikari’, a new rice germplasm in the ‘Koshihikari’ genetic background

Abstract

SummaryDwarfing in rice has dramatically improved and stabilized rice yields worldwide, often controlled by a single dwarf gene,sd1. A novel semidwarf gened60complements the gametic lethal genegal, such that the F1between ‘Hokuriku 100’ (genotyped60d60GalGal,Gal: mutant non-lethal allele) and ‘Koshihikari’ (D60D60galgal,D60: tall allele) would show 25% sterility due to deterioration of gametes bearing bothgalandd60. The F2would segregate as one semidwarf (1d60d60GalGal) : two tall and 25% sterile (2D60d60Galgal) : six tall (2D60d60GalGal: 1D60D60GalGal: 2D60D60Galgal: 1D60D60galgal), skewed from a Mendelian segregation ratio of one semidwarf : three tall for a single recessive gene. To pyramidd60andsd1, into the Japanese super-variety ‘Koshihikari’, the F1(D60d60Galgal) of ‘Koshihikari’ × ‘Hokuriku 100’ was first backcrossed with ‘Koshihikari’, and the BCF1segregated into a ratio of one tall and 25% sterile (D60d60Galgal): two tall (1D60D60Galgal: 1D60D60galgal). Tall, 25% sterile BC1F1plants (D60d60Galgal) were then selected for pollen sterility and backcrossed with ‘Koshihikari’ as the recurrent parent. It is unnecessary to grow out and select a semidwarf from the BCnF2if a pollen parent with ∼70% pollen fertility is chosen from the BCnF1to backcross with the recurrent parent. Semidwarfing genesd60andsd1were successfully pyramided into the ‘Koshihikari’ genome by crossing isogenic lines ‘Koshihikarid60’ and ‘Koshihikarisd1’, to produce ‘Minihikari’, a new parental source of bothd60andsd1. ‘Minihikari’ displayed super-short stature due to the combination ofsd1andd60, which are genetically and functionally independent.