RAD sequencing of mapping population of Bassia scoparia segregating for dicamba resistance

The study is aimed at discovering the genetic basis of dicamba resistance in a population of Bassia scoparia from eastern Colorado. Two F3 families from independent bi-parental crosses between dicamba-resistant and -sensitive plants were grown, genotyped using RAD sequencing, and tested for dicamba resistance through spraying with 560 g ha-1 dicamba when the plants were ~10 cm. Visual injury rating was taken 21 days after treatment to quantify resistance. No selection was made during the F1 or F2 generations, but the cross was validated with a molecular marker for the male parent in the F1. It was found that resistance segregated with the gene IAA16, previously implicated in resistance to auxin herbicides including dicamba. A retrotransposon insertion in the second exon of IAA16 causes differential splicing between biotypes that results in a mutated degron domain that reduces association of IAA16 with TIR1.