TITLE:
Target Site-Based Resistance to ALS Inhibitors, Glyphosate, and PPO Inhibitors in an Amaranthus palmeri Accession from Mississippi
AUTHORS:
Vijay K. Nandula, Darci A. Giacomini, William T. Molin
KEYWORDS:
Amaranthus palmeri, ALS Inhibitors, Glyphosate, Palmer Amaranth, PPO Inhibitors, Resistance
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.11 No.8,
August
11,
2020
ABSTRACT: Extensive acceptance of glyphosate-resistant (GR)
row crops coupled with the simultaneous increase in glyphosate usage has sped
the evolution of glyphosate resistance in economically important weeds. GR Amaranthus palmeri populations are
widespread across the state with some exhibiting multiple resistance to
acetolactate synthase (ALS) inhibiting herbicides such as pyrithiobac. A GR and
ALS inhibitor-resistant accession was also resistant to the protoporphyrinogen
oxidase (PPO) inhibiting herbicide fomesafen. The PPO inhibitor resistance
profile and multiple herbicide resistance mechanisms in this accession were investigated. In addition to fomesafen, resistance
to postemergence applications of acifluorfen, lactofen, carfentrazone,
and sulfentrazone was confirmed. There was no resistance to preemergence
application of fomesafen, flumioxazin, or oxyfluorfen. Molecular analysis of
the ALS gene indicated the
presence of point mutations leading to single nucleotide substitutions at
codons 197, 377, 574, and 653, resulting in proline-to-serine,
arginine-to-glutamine, tryptophan-to-leucine, and serine-to-asparagine
replacements, respectively. The resistant accession contained up to 87-fold
more copies of the EPSPS gene
compared to a susceptible accession. A mutation leading to a deletion of glycine
at codon 210 (ΔG210) of PPO2 gene was also detected. These results indicate that the mechanism of resistance
in the Palmer amaranth accession is target-site based, i.e., altered target site
for ALS and PPO inhibitor resistance and gene amplification for glyphosate
resistance.