Combining two semidwarfing genes d60 and sd1 for reduced height in ‘Minihikari’, a new rice germplasm in the ‘Koshihikari’ genetic background
2012
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 BCₙF₂ if a pollen parent with ∼70% pollen fertility is chosen from the BCₙF₁ 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.
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