Pyroxsulam Resistance in Apera spica-venti: An Emerging Challenge in Crop Protection

Area of Science:

• Agricultural Science
• Plant Biology
• Weed Science

Background:

• Frequent use of ALS-inhibiting herbicides has led to resistance in Apera spica-venti, a common weed in Czech winter wheat.
• A specific biotype resistant to pyroxsulam, with cross-resistance to other herbicides, has been identified.

Purpose of the Study:

• To investigate the mechanisms of herbicide resistance in a pyroxsulam-resistant Apera spica-venti biotype.
• To determine the role of target-site mutations, enhanced metabolism, and herbicide uptake/translocation in resistance.

Main Methods:

• Dose-response experiments were conducted to quantify resistance levels.
• Biochemical assays using malathion and NBD-Cl were performed to assess the involvement of cytochrome P450s and GSTs.
• Gene analysis of the acetolactate synthase (ALS) gene and enzyme activity assays were carried out.
• Studies with 14C-labeled pyroxsulam investigated absorption and translocation.

Main Results:

• High resistance factors (RF) to pyroxsulam were observed in both R1 (6.69) and R2 (141.65) biotypes.
• Malathion pre-treatment reduced RF, suggesting cytochrome P450 involvement, while NBD-Cl affected R2, indicating possible GST involvement.
• No mutations or overexpression were found in previously identified ALS gene sites, but ALS enzyme activity differed significantly between resistant and susceptible biotypes.
• Reduced absorption and translocation were ruled out as primary resistance mechanisms.

Conclusions:

• Herbicide resistance in Apera spica-venti is multifactorial, involving enhanced metabolism (CytP450s, GSTs) and likely target-site resistance due to unidentified ALS mutations.
• The study underscores the adaptive evolution of weed populations under herbicide selection pressure.
• Alternative weed control strategies are necessary to manage resistant Apera spica-venti populations.