Tribenuron-methyl resistance and mutation diversity of the AHAS gene in shepherd's purse (Capsella bursa-pastoris (L.) Medik.) in Henan Province, China.

Shepherd's purse is a troublesome dicot weed that occurs in the major wheat-producing areas in China. Twenty-eight shepherd's purse populations were collected from winter wheat-planting areas in Henan Province and used to evaluate tribenuron-methyl resistance and acetohydroxyacid synthase (AHAS) gene-mutation diversity. The results indicate that all 28 shepherd's purse populations were resistant to tribenuron-methyl at different levels compared with the susceptible population. Mutation of the 197 codon (CCT) changed proline (Pro) into tyrosine (Tyr), histidine (His), leucine (Leu), serine (Ser), arginine (Arg), alanine (Ala) and threonine (Thr), whereas mutation of the 574 codon (TGG) changed tryptophan (Trp) into leucine (Leu). Among these amino acid changes, a co-concurrence of Pro197Leu and Trp574Leu substitutions was identified for the first time in resistant weed species. Furthermore, Pro197Tyr, Pro197Arg and Pro197Ala substitutions have not been previously reported in shepherd's purse. The results of the in vitro AHAS assay suggest that an insensitive AHAS is likely involved in the resistance to tribenuron-methyl in the R populations with AHAS gene mutations, and the non-target-site based resistance might exist in some populations.