Ile-1781-Leu and Asp-2078-Gly Mutations in ACCase Gene, Endow Cross-resistance to APP, CHD, and PPZ in Phalaris minor from Mexico
Cruz Hipólito, Hugo E.; Fernández Moreno, Pablo Tomás; Alcántara-de la Cruz, Ricardo; Gherekhloo, Javid; Osuna Ruiz, M.D.; Prado Amián, Rafael de
Herbicides that inhibit acetyl coenzyme A carboxylase (ACCase) are commonly
used in Mexico to control weedy grasses such as little seed canarygrass (Phalaris minor).
These herbicides are classified into three major families (ariloxyphenoxypropionates (APP),
cyclohexanodiones (CHD), and, recently, phenylpyrazolines (PPZ)). In this work, the resistance
to ACCase (APP, CHD, and PPZ) inhibiting herbicides was studied in a biotype of
Phalaris minor (P. minor) from Mexico, by carrying out bioassays at the whole-plant level
and investigating the mechanism behind this resistance. Dose-response and ACCase in vitro
activity assays showed cross-resistance to all ACCase herbicides used. There was no
difference in the absorption, translocation, and metabolism of the 14C-diclofop-methyl between
the R and S biotypes. The PCR generated CT domain fragments of ACCase from the R
biotype and an S reference were sequenced and compared. The Ile-1781-Leu and Asp-2078-Gly
point mutations were identified. These mutations could explain the loss of affinity for
ACCase by the ACCase-inhibing herbicides. This is the first report showing that this substitution confers resistance to APP, CHD, and PPZ herbicides in P. minor from Mexico.
The mutations have been described previously only in a few cases; however, this is the first
study reporting on a pattern of cross-resistance with these mutations in P. minor. The findings
could be useful for better management of resistant biotypes carrying similar mutations.
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