Glyphosate resistance in a Chilean Lolium multiflorum

Area of Science:

• Agricultural Science
• Plant Biology
• Weed Science

Background:

• Glyphosate resistance in Lolium multiflorum (Italian ryegrass) is a growing concern in South Chile's cereal crops.
• Previous observations indicate poor control of certain Italian ryegrass biotypes with glyphosate.

Purpose of the Study:

• To investigate the physiological and biochemical mechanisms underlying glyphosate resistance in the Vil-1 biotype of Lolium multiflorum.
• To compare glyphosate uptake, translocation, and efficacy between resistant (Vil-1) and susceptible (S) biotypes of Italian ryegrass.

Main Methods:

• Determined glyphosate efficacy by measuring the concentration required to reduce shoot length (ED50) in seedlings.
• Assessed spray retention and leaf surface contact angles (adaxial and abaxial).
• Quantified glyphosate uptake and translocation using 14C-glyphosate in treated leaves and roots.

Main Results:

• The Vil-1 biotype required 7.3-fold higher glyphosate concentration for 50% shoot length reduction compared to the susceptible biotype.
• Spray retention was higher on the susceptible biotype. Abaxial leaf surface contact angles differed significantly (42° on S vs. 63° on Vil-1).
• Glyphosate uptake was greater through the abaxial surface of the susceptible biotype. In resistant biotypes, 14C-glyphosate accumulated in the foliar apex and showed altered distribution.

Conclusions:

• Glyphosate resistance in the Vil-1 Lolium multiflorum biotype is associated with reduced uptake through the abaxial leaf surface.
• Altered glyphosate translocation patterns, with higher accumulation in the foliar apex of resistant biotypes, contribute to resistance.
• Understanding these mechanisms is crucial for developing effective weed management strategies against resistant Italian ryegrass.