INHERITANCE OF DICLOFOP RESISTANCE IN WILD OAT (AVENA-FATUA L.) BIOTYPES FROM THE WILLAMETTE VALLEY OF OREGON

Inheritance of resistance to diclofop was studied in three wild oat bi otypes (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 F-1 plant were spotted wit h diclofop as a nondestructive test for resistance or susceptibility. All F-1 hybrids were resistant, indicating that resistance is dominant and is under nuclear control. The F-2 plants where Monida was the mat ernal parent were screened with diclofop, and F-2 plants of the Monida /C cross were screened with fenoxaprop because the parent C biotype wa s resistant to fenoxaprop. At lower doses, a 3:1 (R:S) segregation rat io in F-2 was observed and at higher doses a 1:3 (R:S) segregation rat io was often observed. The F-2:3 families segregated in a 1:2:1 (all r esistant: segregating resistant and susceptible all susceptible) ratio when treated with a 1.1-kg ae ha(-1) dose of diclofop. This confirms that resistance to diclofop in the B, C, and H biotypes is primarily u nder monogenic control, with resistance being dominant to susceptibili ty at lower herbicide doses. At increased doses, susceptibility become s dominant. Knowledge of the inheritance of resistance may help in the development of containment measures to prevent the spread of herbicid e-resistance genes.