Investigating fluroxypyr resistance in Bassia scoparia

Abstract

Synthetic auxin herbicides are designed to mimic indole-3-acetic acid (IAA), an integral plant hormone affecting cell growth, development, and tropism. Recent developments in synthetic auxin herbicide research have produced several new reports of synthetic auxin resistant weeds and novel resistance mechanisms, including resistance by cytochrome P450 metabolism to mutations in auxin co-receptors. In this document, we investigate specific genes in the auxin signaling pathway that may be involved in weed resistance to the synthetic auxin herbicide fluroxypyr, an economically important method of broadleaf weed control in wheat. The auxin signaling pathway is well characterized, but for many herbicides in the synthetic auxin group, the specific gene family members for receptors and co-receptors with which they interact in the auxin signaling pathway remain unknown. We characterized this Bassia scoparia line using greenhouse studies, dose responses, absorption/translocation and metabolism using 14C-fluroxypyr. To supplement these physiology studies, we conducted an RNA-sequencing experiment using the de novo transcriptome of Bassia scoparia to characterize gene expression in response to fluroxypyr using variant calling and differential expression in R. In addition to investigating this resistance case, this document also describes methodologies for creating crop resistance to pendimethalin via EMS mutagenesis. Through this experiment, many individuals have been found to reach full maturity in the northern Colorado region before the growing season ends. Backcrossing to the inbred parent Sorghum bicolor to begin genetic characterization is the next step following completion of the early maturing line characterization and genetic validation.