AUTHOR=Vázquez-García José G. , Alcántara-de la Cruz Ricardo , Palma-Bautista Candelario , Rojano-Delgado Antonia M. , Cruz-Hipólito Hugo E. , Torra Joel , Barro Francisco , De Prado Rafael 

TITLE=Accumulation of Target Gene Mutations Confers Multiple Resistance to ALS, ACCase, and EPSPS Inhibitors in Lolium Species in Chile

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.553948

DOI=10.3389/fpls.2020.553948

ISSN=1664-462X

ABSTRACT=<p>Different <italic>Lolium</italic> species, common weeds in cereal fields and fruit orchards in Chile, were reported showing isolated resistance to the acetyl CoA carboxylase (ACCase), acetolactate synthase (ALS) and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibiting herbicides in the late 1990s. The first case of multiple resistance to these herbicides was <italic>Lolium multiflorum</italic> found in spring barley in 2007. We hypothesized that other <italic>Lolium</italic> species may have evolved multiple resistance. In this study, we characterized the multiple resistance to glyphosate, diclofop-methyl and iodosulfuron-methyl-sodium in <italic>Lolium rigidum</italic>, <italic>Lolium perenne</italic> and <italic>Lolium multiflorum</italic> resistant (R) populations from Chile collected in cereal fields. <italic>Lolium</italic> spp. populations were confirmed by AFLP analysis to be <italic>L. rigidum</italic>, <italic>L. perenne</italic> and <italic>L. multiflorum</italic>. Dose-response assays confirmed multiple resistance to glyphosate, diclofop-methyl and iodosulfuron methyl-sodium in the three species. Enzyme activity assays (ACCase, ALS and EPSPS) suggested that the multiple resistance of the three <italic>Lolium</italic> spp. was caused by target site mechanisms, except the resistance to iodosulfuron in the R <italic>L. perenne</italic> population. The target site genes sequencing revealed that the R <italic>L. multiflorum</italic> population presented the Pro-106-Ser/Ala (EPSPS), Ile-2041-Asn++Asp-2078-Gly (ACCase), and Trp-574-Leu (ALS) mutations; and the R <italic>L. rigidum</italic> population had the Pro-106-Ser (EPSPS), Ile-1781-Leu+Asp-2078-Gly (ACCase) and Pro-197-Ser/Gln+Trp-574-Leu (ALS) mutations. Alternatively, the R <italic>L. perenne</italic> population showed only the Asp-2078-Gly (ACCase) mutation, while glyphosate resistance could be due to <italic>EPSPS</italic> gene amplification (no mutations but high basal enzyme activity), whereas iodosulfuron resistance presumably could involve non-target site resistance (NTSR) mechanisms. These results support that the accumulation of target site mutations confers multiple resistance to the ACCase, ALS and EPSPS inhibitors in <italic>L. multiflorum</italic> and <italic>L. rigidum</italic> from Chile, while in <italic>L. perenne</italic>, both target and NTSR could be present. Multiple resistance to three herbicide groups in three different species of the genus <italic>Lolium</italic> in South America represents a significant management challenge.</p>