DIVERSE MUTATIONS IN THE ACETOLACTATE SYNTHASE GENE CONFER CHLORSULFURON RESISTANCE IN KOCHIA (KOCHIA-SCOPARIA) BIOTYPES

The DNA sequence of an 83-base pair region of the acetolactate synthase (ALS) gene was compared for 10 chlorsulfuron-resistant (R) and three chlorsulfuron-susceptible (S) kochia biotypes, Point mutation in the codon for the proline residue at position 173 in Domain A of the ALS protein was observed in seven of 10 R biotypes. Among these seven R biotypes, mutation to threonine, serine, arginine, leucine, glutamine, and alanine was identified, The mechanism of resistance was determined for the R biotypes that did not have mutation in Domain A; all were resistant due to modified ALS, which indicated that at least one non-Domain A mutation site for resistance exists in kochia, Sequence results indicate that multiple mutations for resistance have occurred, and that geographically widespread ALS-inhibitor resistance in kochia is not the result of a single resistance allele.