Inheritance of quizalofop resistance in a smooth barley biotype from South Australia

Abstract

Smooth barley [Hordeum glaucum (Steud.) Tzvelev] has recently evolved resistance to acetyl coenzyme-A carboxylase (ACCase) inhibitors in crop fields of South Australia. Experiments were conducted to determine the inheritance of quizalofop (quizalofop-p-ethyl) resistance in a population of smooth barley. Resistant plants (pollen donor) were crossed with susceptible plants (pollen acceptor) to generate an F₁ generation, and the F₁ hybrid was selfed to produce an F₂ generation. It was observed that the resistant population was >60-fold more resistant to quizalofop as compared with the susceptible population and contained an amino acid change from isoleucine-to-leucine at 1781 in the carboxyl-transferase domain of the ACCase gene. The F₁ individual was confirmed to be heterozygous by sequencing the carboxyl-transferase domain of ACCase, indicating that the inheritance of resistance is nuclear encoded. The F₂ dose–response indicated that quizalofop resistance in smooth barley is conferred by a single partially dominant gene. The F₂ plants segregated in a 3:1 ratio when treated with 6.2 g quizalofop ha⁻¹, and sequencing of the ACCase gene also revealed that resistance alleles segregated in a 1:2:1 ratio, as expected for single-gene inheritance. This study confirms that quizalofop resistance in smooth barley from Australia is inherited by a single, partially dominant nuclear allele encoding a mutation in ACCase that confers resistance at the field rate.