A Stable dw3 Allele in Sorghum and a Molecular Marker to Facilitate Selection

ABSTRACT Dwarfism plays a key role in adapting crops to high‐input production systems by contributing to improved lodging resistance and fertilizer efficiency. In sorghum [ Sorghum bicolor (L.) Moench], four dwarfing mutations have been found that profoundly reduce the stalk height. Notable among these mutations is dwarf‐3 ( dw3 ), even though the phenotype it confers is unstable. The objectives of this research were to identify and characterize a stable mutant allele of the dw3 locus. Polymerase chain reaction (PCR) was used to amplify a region of dw3 containing the 882 bp tandem duplication that is diagnostic for the unstable allele. Analyses of PCR fragments from dwarf sorghum accessions that lacked the duplicated region led to the identification of Tx2737 as a possible carrier of a novel mutant dw3 allele. Sequence analysis confirmed and revealed the presence of a 6 bp deletion in exon 5 of dw3 that eliminates two highly conserved amino acids, Q1275 and R1276, from the enzyme. The frequency of this allele in sorghum germplasm appears to be very low with only 1% of the accessions in the diversity panel exhibiting this deletion. Field trials demonstrated that this allele of dw3 produces a stable dwarf phenotype with no height mutants found in Tx2737 and KS19. The new allele has been coined dw3‐sd2 . The discovery of dw3‐sd2 and a DNA marker assay to facilitate selection will provide an opportunity to replace the unstable dw3 allele currently used in most commercial sorghum hybrids through introgression of dw3‐sd2 into elite parent lines.