Resistance to Acetyl-Coenzyme A Carboxylase-Inhibiting Herbicides in Grain Sorghum.

With limited herbicide options and lack of interest in developing new herbicides for grain sorghum, researchers are looking at existing herbicides and, if required, the corresponding genetic resistance. We evaluated a wild Sorghum bicolor (L.) Moench biotype to determine the level and cause of resistance to acetyl-coenzyme A carboxylase-inhibiting herbicides and the ability to transfer the resistance to elite sorghum parents. Dose response and segregation studies were preformed in the greenhouse on the wild biotype, elite sorghum line Tx623, and their progeny. Sequencing portions of the acetyl-coenzyme A carboxylase gene were preformed on locations reported to provide resistance in literature. We found high levels of resistance to aryloxyphenoxypropionates (APP), fluazifip and quizalofop, with GR₅₀ values compared against the susceptible Tx623 206 and 228 fold higher in the wild biotype and 63 and 38 fold higher in the F₁ progeny for the two herbicides, respectively. Cyclohexanedione (CHD) herbicides, sethoxydime and clethodim, did not have a calculable difference in GR₅₀ values between genotypes compared to susceptible Tx623.  These results are in agreement with our gene sequencing which showed a tryptophan to cysteine mutation at location 2027. This mutation is known to provide resistance to APP but not CHD herbicides.  The segregation experiment supports a single major gene model which is expected with this mutation. This biotype shows great promise as a source of resistance for the grain sorghum industry with resistance at field rates to APP herbicides.