A Second Locus, Ixr B1 in Arabidopsis thaliana, that Confers Resistance to the Herbicide Isoxaben

An isoxaben resistant mutant of Arabidopsis thaliana is described whose locus, Ixr B1, is unlinked genetically to the previously described resistance locus Ixr A (DR Heim, JL Roberts, PD Pike, IM Larrinua [1989] Plant Physiol 90: 146-150). A cross of strains each homozygous for one of these two resistance loci gives rise to some isoxaben sensitive F(2) progeny. Growth curves versus isoxaben of this mutant, its F(1) progeny and the wild-type parent strain showed that this locus displays a weakly codominant Mendelian phenotype. Callus cultures were established from plants homozygous as well as heterozygous for this locus. Growth inhibition curves done with these cultures mimic the data obtained in vivo.