Molecular characterization and inheritance of resistance to ACCase-inhibiting herbicides in Lolium rigidum.

The molecular basis and mode of inheritance of resistance to ACCase-inhibiting herbicides were investigated in a biotype of Lolium rigidum Gaud that has been discovered in Israel. Dose-response experiments at the whole-plant level have revealed that the resistant biotype was more resistant (6.3- to 40-fold) than the susceptible wild-type to ACCase-inhibiting herbicides. A 276-bp genomic DNA encoding the carboxyltransferase domain within the chloroplastic ACCase from resistant and susceptible biotypes were amplified by PCR and analyzed. Sequence comparison revealed that a single isoleucine-to-leucine substitution differentiated ACCases from susceptible and resistant biotypes (corresponds to residue 1769 of wheat ACCase, Ace No AF029895). A PCR amplification of specific alleles (PASA) method was developed to detect the allele composition leading to isoleucine-leucine mutation. ACCase extracted from homozygote resistant, heterozygote and homozygote susceptible plants showed IC₅₀ values of 25.8, 5.6 and 0.6 µM, respectively, suggesting that alteration in the ACCase is governed by a co-dominant gone. The inheritance studies confirmed that the resistance of L rigidum to ACCase-inhibiting herbicides is governed by a single, nuclear and co-dominant gene. [ABSTRACT FROM AUTHOR]