Inheritance of diclofop resistance in wild oat (Avena fatuaL.) biotypes from the Willamette Valley of Oregon

Abstract

Inheritance of resistance to diclofop was studied in three wild oat biotypes (designated B, C., and H) from the Willamette Valley of Oregon. Cultivated oat (cultivar ‘Monida’) was crossed, including reciprocals, to three wild oat biotypes. Leaves of each F1plant were spotted with diclofop as a nondestructive test for resistance or susceptibility. All F1hybrids were resistant, indicating that resistance is dominant and is under nuclear control. The F2plants where Monida was the maternal parent were screened with diclofop, and F2plants of the Monida/C cross were screened with fenoxaprop because the parent C biotype was resistant to fenoxaprop. At lower doses, a 3:1 (R:S) segregation ratio in F2was observed and at higher doses a 1:3 (R:S) segregation ratio was often observed. The F2:3families segregated in a 1:2:1 (all resistant : segregating resistant and susceptible all susceptible) ratio when treated with a 1.1-kg ae ha−1dose of diclofop. This confirms that resistance to diclofop in the B, C, and H biotypes is primarily under monogenic control, with resistance being dominant to susceptibility at lower herbicide doses. At increased doses, susceptibility becomes dominant. Knowledge of the inheritance of resistance may help in the development of containment measures to prevent the spread of herbicide-resistance genes.