ARS | Publication request: Transfer of herbicide-resistant gene to weedy rice populations and its implications

Submitted to: International Weed Science Congress
Publication Type: Proceedings
Publication Acceptance Date: April 30, 2008
Publication Date: June 22, 2008
Citation: Shivrain, V.K., Burgos, N.R., Sales, M.A., Smith, K.L., Gealy, D.R., Kuk, Y.I., Mauromoustakos, A. 2008. Transfer of herbicide-resistant gene to weedy rice populations and its implications. International Weed Science Congress.

Technical Abstract: Red rice diversity in terms of phenology, sexual compatibility with cultivated rice, and the wide window of rice planting time can affect the rate of herbicide-resistant gene transfer from rice to RR. Experiments were conducted to a) determine the effect of red rice, rice cultivar, and planting date on outcrossing rate, b) evaluate phenotypes of outcrosses, and c) assess sexual compatibility between rice and red rice biotypes. Clearfield (CL) rice cultivars CL161 and CL hybrid rice were planted with 12 RR biotypes on four planting dates in 2005 and 2006. Red rice seed was harvested at maturity and a sub-sample was planted in subsequent years. Red rice seedlings were tested for resistance to imazethapyr. The survivors were confirmed as outcrosses by DNA analysis and were characterized at maturity. Manual crosses were also performed between red rice biotypes and CL161 to determine their sexual compatibility. The outcrossing rate of different RR biotypes varied from 0.01 to 0.20 and 0.03 to 0.52% with CL161 and CL hybrid rice, respectively. CL hybrid rice had higher outcrossing with all red rice biotypes than did CL161. Outcrossing rate differed between red rice biotypes in the same planting date due to variability in their flowering time. Brownhull RR had the highest outcrossing rate followed by blackhull and strawhull types. CL161 x red rice outcrosses were phenotypically uniform unlike the CL hybrid rice x red rice outcrosses, which segregated. Differences in outcrossing rate between red rice biotypes and CL cultivars are also dependent on their sexual compatibility. These experiments demonstrate that various factors affecting outcrossing rate need to be considered in planning gene flow mitigation strategies for rice.