Experiments were conducted to determine the inheritance of resistance in crosses between imazethapyr-resistant rice and red rice. Past experiments on red rice control, using the Clearfield rice technology, resulted in outcrossing between Clearfield rice and Stuttgart strawhull red rice. The F2 generation of these spontaneous crosses were characterized with respect to inheritance of imazethapyr resistance, leaf color and leaf pubescence, and seed shattering, pubescence, color, and size. Agronomic traits of hybrids were also observed in relation to their parents. To determine the segregation of resistance among F2 phenotypes, the response of three- to four-leaf plants to imazethapyr was scored 3 wk after application as resistant (R, no imazethapyr symptoms), susceptible (S, death of plants), or intermediate (I, stunted plants). R, I, and S phenotypes segregated in a 1:2:1 ratio in the F2 generation. Two- or three-gene inheritance was documented for leaf and seed characteristics. A wide range in onset of flowering (70 to 130 d after planting) was observed in F2 families, although 6% of the plants did not flower during the growing season. F2 plants were taller and had more tillers than any of their parents. Resistance to imazethapyr is associated with a single, incompletely dominant allele.
Nomenclature: Imazethapyr; red rice, Oryza sativa L. #3 ORYSA; rice, Oryza sativa L.; ‘CL121’, ‘CL161’.
Additional index words: Imazethapyr-tolerant rice, outcrossing.
Abbreviations: ALS, acetolactate synthase (EC 22.214.171.124); CL, ‘Clearfield’ rice; DAP, days after planting; RR, red rice; RREC, Rice Research and Extension Center; WAP, weeks after planting; WAT, weeks after treatment.