Target-site mutation accumulation among ALS inhibitor-resistant Palmer amaranth

Area of Science:

• Agricultural Science
• Plant Science
• Weed Science

Background:

• Palmer amaranth (Amaranthus palmeri) is a significant agricultural weed in the USA.
• Widespread resistance to acetolactate synthase (ALS) inhibitors is documented in Arkansas Palmer amaranth populations.
• The specific cross-resistance patterns and underlying resistance mechanisms were previously unknown.

Purpose of the Study:

• To investigate the cross-resistance profiles of Palmer amaranth to various ALS inhibitors.
• To identify target-site mutations conferring resistance in Palmer amaranth populations across Arkansas.
• To understand the genetic basis of herbicide resistance in this problematic weed.

Main Methods:

• Field surveys were conducted across 20 Palmer amaranth localities in 13 Arkansas counties.
• Plants were tested for cross-resistance to five different ALS inhibitor herbicides.
• DNA analysis was performed to identify target-site mutations in the acetolactate synthase (ALS) gene.

Main Results:

• All tested Palmer amaranth populations displayed cross-resistance to five ALS inhibitors, including imazethapyr and trifloxysulfuron.
• The Trp574Leu mutation in the ALS gene was present in all resistant plants analyzed, confirming it as a primary resistance mechanism.
• Multiple ALS resistance-conferring mutations, including additional target-site mutations, were found in some resistant Palmer amaranth individuals.

Conclusions:

• The Trp574Leu mutation is the predominant mechanism for ALS inhibitor resistance in Arkansas Palmer amaranth.
• The widespread resistance indicates that ALS inhibitors are largely ineffective for controlling Palmer amaranth in the mid-south USA.
• Further research is needed to explore potential non-target site resistance mechanisms in highly resistant populations.