Herbicide Resistance in Setaria

The four documented cases of field selection for herbicide resistance in weedy Setaria are described in this chapter. In each case, weed control failure was observed in practice in the field. In all cases, resistance was target-site-based resistance and was due to single nucleotide mutations causing amino-acid substitutions at codon 264 of psbA (photosystem II inhibitors), codons 136 and 239 of alpha 2-tubulin (tubulin polymerization inhibitors), codon 1781 of acetyl-CoA carboxylase (acetyl-CoA carboxylase inhibitors), or codons 653 or 654 of acetolactate-synthase (acetolactate-synthase inhibitors). The heredity of resistance in these cases was maternal, nuclear recessive, nuclear dominant, or partially dominant, respectively. Pleiotropic effects of the mutant alleles were observed on seed production for the herbicide-resistant alleles Gly-264 of psbA and Ile-239 of alpha 2-tubulin (22 % yield reduction for both alleles), but not for the Leu-1781 acetyl-CoA carboxylase allele. These alleles were introgressed in foxtail millet (S. italica) to develop herbicide-resistant genetic resources and germplasm with the aim to produce and release elite varieties of foxtail millet. This material was also used to study pollen dispersal and possible gene flow between weedy Setaria and cultivated foxtail millet.