Confirmation and inheritance of glufosinate resistance in an Amaranthus palmeri population from North Carolina.

A putative glufosinate-resistant Amaranthus palmeri population was reported in 2015 in Anson County, North Carolina. The results from dose-response assays conducted in the field suggested plants were surviving lethal rates of glufosinate. Dose-response assays conducted in the glasshouse determined the Anson County accession exhibited reduced susceptibility to glufosinate compared to three glufosinate-susceptible populations. The LD₅₀ values (210-316 g ai ha^-1) for the Anson County population were always higher than the LD₅₀ values (118-158 g ai ha^-1) for the tested susceptible populations from the dose-response assays. Anson County plants that survived lethal glufosinate rates were reciprocally crossed with susceptible plants to create F₁ genotypes and treated with a lethal rate of glufosinate (267 g ai ha^-1; ascertained from glasshouse dose-response assay) to determine the distribution of injury and survival for each cross compared to a cross of susceptible parents. The distribution of injury was non-normal for the crosses containing an Anson County plant compared to the cross with a susceptible parent. Survival was 68%-84% for crosses containing an Anson County plant, whereas the survival was significantly reduced to 35% for the susceptible plant cross. Chi-square goodness of fit tests were used to test inheritance models to describe the responses of the genotypes. The resistant × susceptible crosses were best described with a heterozygous two loci with incomplete dominance model compared to the resistant × resistant cross that was best described with a heterozygous single locus with incomplete dominance model. The Anson County population has evolved resistance to glufosinate that is heritable and likely conferred by an oligogenic mechanism with incomplete dominance.