Combining two semidwarfing genes d60 and sd1 for reduced height in 'Minihikari', a new rice germplasm in the 'Koshihikari' genetic background

Abstract

Dwarfing in rice has dramatically improved and stabilized rice yields worldwide, often controlled by a single dwarf gene, sd1. A novel semidwarf gene d60 complements the gametic lethal gene gal, such that the F1 between 'Hokuriku 100' (genotype d60d60GalGal, Gal: mutant non-lethal allele) and 'Koshihikari' (D60D60galgal, D60: tall allele) would show 25% sterility due to deterioration of gametes bearing both gal and d60. The F2 would segregate as one semidwarf (1 d60d60GalGal): two tall and 25% sterile (2 D60d60Galgal): six tall (2 D60d60GalGal: 1 D60D60GalGal: 2 D60D60Galgal: 1 D60D60galgal), skewed from a Mendelian segregation ratio of one semidwarf: three tall for a single recessive gene. To pyramid d60 and sd1, into the Japanese super-variety 'Koshihikari', the F1 (D60d60Galgal) of 'Koshihikari' × 'Hokuriku 100' was first backcrossed with 'Koshihikari', and the BCF1 segregated into a ratio of one tall and 25% sterile (D60d60Galgal): two tall (1 D60D60Galgal 1 D60D60galgal). Tall, 25% sterile BC1F1 plants (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 BC n F2 if a pollen parent with ∼70% pollen fertility is chosen from the BC n F1 to backcross with the recurrent parent. Semidwarfing genes d60 and sd1 were successfully pyramided into the 'Koshihikari' genome by crossing isogenic lines 'Koshihikari d60' and 'Koshihikari sd1', to produce 'Minihikari', a new parental source of both d60 and sd1. 'Minihikari' displayed super-short stature due to the combination of sd1 and d60, which are genetically and functionally independent. Copyright © 2012 Cambridge University Press.