Resistance to herbicides can be due to alteration(s) of the herbicide target site (target-site resistance, TSR) or to other mechanisms (non-target-site resistance, NTSR). We investigated the diversity of mechanisms conferring resistance to herbicides inhibiting acetolactate synthase (ALS) in corn poppy (Papaver rhoeas). We developed PCR-based assays enabling to genotype ALS codons involved in resistance to detect TSR poppy plants. The accuracy of these assays was checked by genotyping a total of 888 poppy plants from France and Italy, then sequencing ALS in these plants. The sequence data enabled to characterise the diversity of mutant ALS alleles involved in TSR. Six mutant ALS alleles, Arg197, His197, Leu197, Ser197, Thr197 and Leu574 were identified in the 888 plants analysed, with Leu574 identified in a single plant. Different mutant alleles were found in a same population or a same plant. Our data indicated that TSR evolved by multiple, independent appearances in poppy. We established the cross-resistance patterns associated to the mutant ALS identified by assessing the sensitivity of 729 plants to three ALS inhibitors using bioassays, and subsequently genotyping and sequencing these plants. All mutant ALS alleles conferred dominant resistance to the field rate of the sulfonylurea tribenuron and moderate or no resistance to the field rate of the triazolopyrimidine florasulam. Depending on the allele, dominant or partially dominant resistance to the field rate of the imidazolinone imazamox was observed. We observed that plants with identical genotypes at ALS could be resistant, moderately resistant or sensitive to an herbicide. The observed variation in sensitivity among plants with identical genotypes at ALS occurred in 420 plants out of 729 (57.6%). This clearly suggests that TSR alone does not explain all the variation in sensitivity we observed. The most likely hypothesis explaining the variation in sensitivity not due to TSR is the occurrence of NTSR mechanisms conferring resistance to ALS inhibitors. The existence of NTSR mechanisms was confirmed by our observing three plants resistant to imazamox while not carrying mutant ALS alleles among the 729 analysed. In the populations we studied, it seems likely that a majority of plants contain both TSR and NTSR mechanisms. The molecular diagnosis assays targeting ALS codons involved in resistance in poppy developed in this work will facilitate the detection of TSR in poppy field populations. Our data also shows that resistance to ALS inhibitors in poppy clearly evolved by redundant evolution of a set of mutant ALS alleles and most likely of NTSR mechanisms, the nature of which remains to be investigated.
A diversity of mechanisms endows resistance to ALS inhibitors in poppy
2011
Abstract
Resistance to herbicides can be due to alteration(s) of the herbicide target site (target-site resistance, TSR) or to other mechanisms (non-target-site resistance, NTSR). We investigated the diversity of mechanisms conferring resistance to herbicides inhibiting acetolactate synthase (ALS) in corn poppy (Papaver rhoeas). We developed PCR-based assays enabling to genotype ALS codons involved in resistance to detect TSR poppy plants. The accuracy of these assays was checked by genotyping a total of 888 poppy plants from France and Italy, then sequencing ALS in these plants. The sequence data enabled to characterise the diversity of mutant ALS alleles involved in TSR. Six mutant ALS alleles, Arg197, His197, Leu197, Ser197, Thr197 and Leu574 were identified in the 888 plants analysed, with Leu574 identified in a single plant. Different mutant alleles were found in a same population or a same plant. Our data indicated that TSR evolved by multiple, independent appearances in poppy. We established the cross-resistance patterns associated to the mutant ALS identified by assessing the sensitivity of 729 plants to three ALS inhibitors using bioassays, and subsequently genotyping and sequencing these plants. All mutant ALS alleles conferred dominant resistance to the field rate of the sulfonylurea tribenuron and moderate or no resistance to the field rate of the triazolopyrimidine florasulam. Depending on the allele, dominant or partially dominant resistance to the field rate of the imidazolinone imazamox was observed. We observed that plants with identical genotypes at ALS could be resistant, moderately resistant or sensitive to an herbicide. The observed variation in sensitivity among plants with identical genotypes at ALS occurred in 420 plants out of 729 (57.6%). This clearly suggests that TSR alone does not explain all the variation in sensitivity we observed. The most likely hypothesis explaining the variation in sensitivity not due to TSR is the occurrence of NTSR mechanisms conferring resistance to ALS inhibitors. The existence of NTSR mechanisms was confirmed by our observing three plants resistant to imazamox while not carrying mutant ALS alleles among the 729 analysed. In the populations we studied, it seems likely that a majority of plants contain both TSR and NTSR mechanisms. The molecular diagnosis assays targeting ALS codons involved in resistance in poppy developed in this work will facilitate the detection of TSR in poppy field populations. Our data also shows that resistance to ALS inhibitors in poppy clearly evolved by redundant evolution of a set of mutant ALS alleles and most likely of NTSR mechanisms, the nature of which remains to be investigated.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
