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

Abstract

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% (GR50) of 45 and 1,331 g ae ha−1for the susceptible and resistant populations, respectively. F1crosses were made between resistant and susceptible inbred individuals by hand-pollination, and the F1plants were selfed to produce F2plants. The F2population was screened with 280 g ha−1dicamba, a rate that could discriminate between susceptible and resistant plants. A total of eight F2families were screened twice. In the first screen, seven F2families segregated in a 3:1 ratio, consistent with a single dominant allele controlling resistance, and in the second screen six F2families segregated in a 3:1 ratio. F2individuals were selfed, the F3progeny were tested with 280 g ha−1dicamba, and the genotype of each F2parent was determined based on F3progeny segregation. F3family segregation was consistent with the F2parents 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.