Inheritance of herbicide resistance in two germplasm lines of Clearfield* rice (Oryza sativa L.)

Inheritance of imidazolinone resistance in two germplasms of Clearfield rice lines, 93AS3510 and PWC-16, was studied using parents, F-1 hybrids, F-2 populations, and F-2:3 families. Germination tests were conducted in Petri dishes under controlled environments to reveal any discrete phenotypic responses to herbicide treatments. PWC-16 has a herbicide resistance level 4.9 times higher than that of 93AS3510. A concentration of 1 mg L-1 a.i. (active ingredient) of imazethapyr herbicide produced three distinctive response types in 93AS3510 crosses, while a concentration of 10 mg L-1 was required to differentiate the three response types in PWC-16 crosses. The segregation of the herbicide-resistant gene from both Clearfield rice lines fit into the Mendelian 1:2:1 (susceptible: intermediate:resistant) ratio. There was no maternal effect associated with the inheritance of the trait. The imidazolinone resistance, therefore, is governed by a single incomplete dominant nuclear gene. The F-1 hybrid from a cross between resistant and non-resistant lines will produce resistant plants. Clearfield rice provides an effective use of imidazolinone herbicides to control red rice, the most troublesome weed of rice, along with other rice weeds. Preventing transfer of the herbicide-resistant gene into red rice is crucial to maintain its effectiveness.