Convergent Adaptation of Multiple Herbicide Resistance to
Auxin Mimics and ALS- and EPSPS-Inhibitors in Brassica rapa
from North and South America
José Alfredo Dominguez-Valenzuela¹ , Candelario Palma-Bautista²,* , José G. Vazquez-Garcia² , Marcos Yanniccari³,*, Ramón Gigón⁴, Ricardo Alcántara-de la Cruz⁵ , Rafael De Prado² and João Portugal^6,7
1 Department of Agricultural Parasitology, Chapingo Autonomous University, Texcoco 56230, Mexico; jose_dv001@yahoo.com.mx
2 Department Agroforestry, Biochemistry andMolecular Biology, University of Cordoba, 14014 Cordoba, Spain; z82vagaj@uco.es (J.G.V.-G.); qe1pramr@uco.es (R.D.P.)
3 Chacra Experimental Integrada Barrow (MDA-INTA), National Scientific and Technical Research

Abstract:

Herbicide-resistant weeds have been identified and recorded on every continent where croplands are available. Despite the diversity of weed communities, it is of interest how selection has led to the same consequences in distant regions. Brassica rapa is a widespread naturalized weed that is found throughout temperate North and South America, and it is a frequent weed among winter

cereal crops in Argentina and in Mexico. Broadleaf weed control is based on glyphosate that is used prior to sowing and sulfonylureas or mimic auxin herbicides that are used once the weeds have already emerged. This study was aimed at determining whether a convergent phenotypic adaptation to multiple herbicides had occurred in B. rapa populations from Mexico and Argentina by comparing the herbicide sensitivity to inhibitors of the acetolactate synthase (ALS), 5-enolpyruvylshikimate-3- phosphate (EPSPS), and auxin mimics. Five B. rapa populations were analyzed from seeds collected in wheat fields in Argentina (Ar1 and Ar2) and barley fields in Mexico (Mx1, Mx2 and MxS). Mx1, Mx2, and Ar1 populations presented multiple resistance to ALS- and EPSPS-inhibitors and to auxin mimics (2,4-D, MCPA, and fluroxypyr), while the Ar2 population showed resistance only to ALSinhibitors and glyphosate. Resistance factors ranged from 947 to 4069 for tribenuron-methyl, from 1.5 to 9.4 for 2,4-D, and from 2.7 to 42 for glyphosate. These were consistent with ALS activity, ethylene production, and shikimate accumulation analyses in response to tribenuron-methyl, 2,4-D, and glyphosate, respectively. These results fully support the evolution of the multiple- and cross herbicide resistance to glyphosate, ALS-inhibitors, and auxinic herbicides in B. rapa populations from Mexico and Argentina. 

Plants 2023, 12, 2119.