Genetic and agronomic analyses of red rice-Clearfield hybrids and their progeny produced from natural and controlled crosses

Clearfield rice technology is a popular method for controlling noxious red rice weeds (Oryza sativa L.) in commercial rice fields in the southern U.S. Previous research has detected red rice-Clearfield variety F₁ hybrids at low rates in Louisiana and Arkansas. The first research objective was to determine genetic control of imazethapyr resistance in F₁ hybrids and F₂ populations derived from natural and controlled hybridizations of red rice and Clearfield rice. The second objective was to characterize and compare agronomic performance of the hybrids and their progeny with Clearfield varieties. Genetic analysis showed that imazethapyr resistance was dominant in all tested F₁ hybrids with single and two-gene inheritance observed across composite F₂ populations. F₁ hybrids exhibited high levels of variation for plant height, heading date, and seven reproductive traits. Heterosis was observed in the hybrids versus Clearfield varieties for plant height, heading date, seed-bearing tillers, panicle length, and spikelets/panicle. While seed production of the F₁ hybrids was generally inferior to that of the commercial varieties, one red rice/CL121 hybrid produced greater seeds/panicle than the CL121 commercial parent. Extensive variation was observed for all measured traits in the F₂ populations derived from either natural or controlled crosses. Results from this study indicate that red rice/Clearfield F₁ hybrids normally exhibit low reproductive seed capacity, but a small proportion of the subsequent F₂ progeny can produce high fecundity levels. Effective stewardship practices are therefore warranted to reduce the occurrence of such hybrids and their offspring to ensure continued success of the Clearfield technology. Approved for publication by the Director of the Louisiana Agricultural Experiment Station as manu number 2008-306-1392.