Resistance to quinclorac and ALS‐inhibitor herbicides in <i>Galium spurium</i> is conferred by two distinct genes

Abstract

Summary Classical Mendelian experiments were conducted to determine the genetics and inheritance of quinclorac and acetolactate synthase (ALS)‐inhibitor resistance in a biotype of Galium spurium . Plants were screened with the formulated product of either quinclorac or the ALS‐inhibitor, thifensulfuron, at the field dose of 125 or 6 g active ingredient (a.i.) ha −1 respectively. Segregation in the F 2 generation indicated that quinclorac resistance was a single, recessive nuclear trait, based on a 1 : 3 segregation ratio [resistant : susceptible (R : S)]. Resistance to ALS inhibitors was due to a single, dominant nuclear trait, segregating in the F 2 generation in a 3 : 1 ratio (R : S). The genetic models were confirmed by herbicide screens of F 1 and backcrosses between the F 1 and the S parent. F 2 plants that survived quinclorac treatment set seed and the resulting F 3 progeny were screened with either herbicide. Quinclorac‐treated F 3 plants segregated in a 1 : 0 ratio (R : S), hence F 2 progenitors were homozygous for quinclorac resistance. In contrast, F 3 progeny segregated into three ratios: 1 : 0, 3 : 1 and 0 : 1 (R : S) in response to ALS‐inhibitor treatment. This segregation pattern indicates that their F 2 parents were either homozygous or heterozygous for ALS‐inhibitor resistance. Therefore, there were clearly two distinct resistance mechanisms encoded by two genes that were not tightly linked as demonstrated by segregation patterns of the F 3 .