Inheritance of Resistance to The Auxinic Herbicide Dicamba in Kochia (Kochia scoparia)

The inheritance of resistance to the auxinic herbicide dicamba was examined in a kochia population from Nebraska. An inbred, resistant line was developed by selection and selfing over seven generations to ensure any resistance alleles would be homozygous in the parents. An inbred, susceptible line was similarly developed, but without selection. Dose–response experiments with dicamba determined a glyphosate-resistant concentration required to inhibit dry weight accumulation by 50% (GR 50 ) of 45 and 1,331 g ae ha −1 for the susceptible and resistant populations, respectively. F 1 crosses were made between resistant and susceptible inbred individuals by hand-pollination, and the F 1 plants were selfed to produce F 2 plants. The F 2 population was screened with 280 g ha −1 dicamba, a rate that could discriminate between susceptible and resistant plants. A total of eight F 2 families were screened twice. In the first screen, seven F 2 families segregated in a 3:1 ratio, consistent with a single dominant allele controlling resistance, and in the second screen six F 2 families segregated in a 3:1 ratio. F 2 individuals were selfed, the F 3 progeny were tested with 280 g ha −1 dicamba, and the genotype of each F 2 parent was determined based on F 3 progeny segregation. F 3 family segregation was consistent with the F 2 parents having a 1:2:1 homozygous-susceptible:heterozygote:homozygous-resistant pattern, confirming that resistance to dicamba in kochia is likely conferred by a single allele with a high degree of dominance.