Resistance of Camelina microcarpa to acetolactate synthase inhibiting herbicides

An accession of Camelina microcarpa suspected to be resistant to sulfonylurea herbicides was identified in Oregon in 1998 field experiments. Greenhouse research confirmed that the putative resistant biotype was resistant to chlorsulfuron and metsulfuron on a whole plant level. Compared with the resistant (R) biotype, the susceptible (S) biotype was 1000 and 10 000-fold more sensitive to metsulfuron and chlorsulfuron respectively. The R biotype was also resistant to other sulfonylurea, sulfonylaminocarbonyl-triazolinone, imidazolinone and triazolopyrimidine herbicides. An in vivo enzyme assay indicated that acetolactate synthase (ALS) from the R plants required 111 times more chlorsulfuron to inhibit activity by 50% compared with the amount required to have a similar effect on ALS from S plants. Analysis of the nucleotide and amino acid sequences demonstrated that a single-point mutation from G to T in the als1 gene conferred the change from the amino acid tryptophan to leucine at position 572 in the resistant biotype. This research confirmed that ALS inhibitor resistance in an Oregon accession of C. microcarpa is based on an altered target site conferred by a single-point mutation.