What question did this study set out to answer?

This research aims to understand the genetic and molecular basis of clopyralid resistance in common ragweed.

January 22, 2026Weed Science0 citationsOpen Access

Unraveling the Genetic and Molecular Changes Associated with Clopyralid Resistance in Common Ragweed ( Ambrosia artemisiifolia )

NHNash D. Hart EHErin C. Hill EPEric L. Patterson

Key Points

This research aims to understand the genetic and molecular basis of clopyralid resistance in common ragweed.
Conducted greenhouse dose response assays using resistant and susceptible common ragweed populations.
Performed test crosses to investigate inheritance patterns.
Utilized RNA-seq for transcriptomic analysis to identify potential resistance genes.
The ED50 for resistant common ragweed was significantly higher than for the susceptible line, indicating strong resistance.
The chi-square tests suggested a multigenic inheritance model for resistance, rejecting a simple single-gene model.
Differential expression analysis identified 70 genes associated with resistance mechanisms in auxin signaling and metabolism.

Abstract

Abstract Common ragweed ( Ambrosia artemisiifolia L.) is a globally distributed, difficult to control weed that can cause severe crop yield losses if not properly managed. Clopyralid is a synthetic auxin herbicide widely used to control A. artemisiifolia and other Asteraceae weeds. In 2016, a highly clopyralid resistant A. artemisiifolia population was reported on a Michigan Christmas tree farm which we call AMBEL-40. We investigated the inheritance and potential clopyralid resistance mechanisms in this population using greenhouse dose response assays, test crosses with a susceptible line - AMBEL-39, and RNA-seq. The ED 50 values for AMBEL-40 and AMBEL-39 were 2,110.8 and 74.5 g ha -1 , respectively; therefore, the R/S ratio is 28.3. Dose response results with triclopyr, fluroxypyr, 2,4-D, or dicamba demonstrate no multiple or cross-resistance in AMBEL-40. AMBEL-40 and AMBEL-39 crossed F 1 generations (M3F1, M3F2, and M1F1) showed increased resistance compared to AMBEL-39 with ED 50 values of 1,379.2, 1,134.0, and 542.5 g ha -1 . Chi-square tests of three sib-mated F 1 to generate F 2 generations rejected a single-gene 1:3 model and supported a two-gene 3:13 segregation, consistent with multigenic inheritance. We identified 23 Aux/IAA transcripts containing the degron sequence in the published Ambrosia artemisiifolia genome, of these, three contained polymorphisms in our RNAseq data, but none consistently co-segregated with resistance. Differential expression analysis identified 70 genes with 39 upregulated and 31 downregulated in AMBEL-40 including candidates in auxin/ethylene signaling, metabolism, cuticular wax biosynthesis, and stress modulation, supporting a non-target site resistance mechanism. Together, these results indicate that clopyralid resistance in A. artemisiifolia is recessive, and multigenic, with potentially altered signaling, metabolism, and uptake as a mechanism of resistance rather than a single Aux/IAA degron mutation.

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