Detection of accase target-site resistant Alopecurus myosuroides huds (black-grass) in Belgian populations

Black-grass is a common grass weed, widely spread in Northern Europe and also in
Belgium. For ages, it has been an increasing problem in industrial crops,
especially winter cereals. The first case of resistance in Belgium was reported in
1996 by Robert Bulcke (Eelen et al., 1996). Yet the resistance mechanism was not
specified. Since then, no more information was published about the evolution
Belgium, while research continued in the United Kingdom and in France. Moreover,
during the last decade, progress in molecular biology allowed to highlight the
mechanism of target-site resistance. A simple PCR method allows to detect the
mutation conferring resistance to herbicide.

After two years of resistance monitoring in Belgium, mostly in the Walloon part,
some populations have been clearly identified as highly resistant to ACCase
inhibitor. These populations have been tested by molecular biology so as to detect
the single nucleotide polymorphism (SNP) involved in this case. The method employed
was the Polymerase Chain Reaction Allele Specific Assays (PASA: Délye, 2002a) for
the mutation Ile-1781-Leu that confers a target-site resistance to ACCase
inhibitors. Those analyses were performed on plant material issued from bioassays,
either in glasshouses or in Petri dishes. Leaves have been collected from plants
which survived a fenoxaprop-P treatment applied in a glasshouse single dose assay.
Seedlings from resistant populations grown in Petri dishes containing either
fenoxaprop-P or cycloxydim provided the second type of sample. Ile1781 mutants were
discovered within three populations. Each mutant plant was heterozygote. Five of
those samples have been sequenced to confirm PASA results and everyone was matching.
Moreover, they were all issued from Petri dishes containing cycloxydim, known to be
unaffected by enhanced metabolism, confirming that theses populations are indeed
target-site resistant.