Abstract:

Background  Johnsongrass (Sorghum halepense (L.) Pers.) is one of the most problematic weeds worldwide, and in recent years, control failures with herbicides inhibiting the enzyme acetolactate synthase (ALS) have been reported.

Objective  Determine the resistance in different biotypes of Johnsongrass to nicosulfuron, as well as elucidate its possible resistance mechanism.

Methods  Dose-response bioassays were conducted with four biotypes, three of them from corn fields with consecutive history of nicosulfuron applications (Veracruz-Mexico) and a susceptible biotype (Guanajuato-Mexico). A partial sequence of the ALS gene was obtained for each biotype to identify mutations conferring target-site resistance to this herbicide.

Results  The dose-response curves showed high rates of resistance in the biotypes from Veracruz (IR: 30, 63, and 77 times more resistant than the susceptible biotype); at the molecular level, a mutation was found, which resulted in the substitution of amino acid (Asp376Glu).

Conclusions  This mutation could be involved in resistance in the Oro Verde, El Marcial, and Francisco Villa populations.

Herbicide Resistance; ALS-Inhibitors; Bioassays; Dose-Response Curve