Factors Affecting the Outcrossing Rate between Clearfield™ Rice and Red Rice (Oryza sativa)

• Published in: Weed science 2009-07, Vol.57 (4), p.394-403
• Main Authors: Shivrain, Vinod K., Burgos, Nilda R., Sales, Marites A., Mauromoustakos, Andy, Gealy, David R., Smith, Kenneth L., Black, Howard L., Jia, Melissa
• Format: Article
• Language: English
• Subjects: Acetolactate synthase (ALS); air temperature; biosafety; biotypes; crop plants as weeds; Crop science; cultivars; field experimentation; Flowering; flowering synchrony; Gene flow; genetic markers; grass weeds; herbicide resistance; Hybridity; imazethapyr; imazethapyr-resistant rice; inbred lines; microsatellite repeats; molecular sequence data; Oryza sativa; outcrossing; phenology; Planting; Planting date; Plants; Pollen; pollen flow; relative humidity; Rice; temporal variation; Transgenic plants; WEED BIOLOGY AND ECOLOGY; weedy relatives
• ISSN: 0043-1745; 1550-2759
• DOI: 10.1614/WS-09-003.1

The commercialization of imazethapyr-resistant (Clearfield™, CL) rice in the southern United States has raised serious concerns about gene flow to red rice, producing imazethapyr-resistant red rice populations. Our objectives were to determine the impact of planting date, CL cultivars, and red rice biotypes on outcrossing rate; and to investigate the relative contribution of flowering time of CL rice and red rice biotypes, together with air temperature and relative humidity (RH), on outcrossing rate. Field experiments were conducted at Stuttgart, Rohwer, and Kibler, AR, from 2005 to 2007, at three or four planting times from mid-April to late May. ‘CL161’ (inbred cultivar) and ‘CLXL8’ (hybrid) rice were planted in nine-row plots, with red rice planted in the middle row. Twelve red rice biotypes were used. The flowering of red rice and CL rice, air temperature, and RH were recorded. Red rice seeds were collected at maturity. To estimate outcrossing rate, resistance to imazethapyr was evaluated in subsequent years and confirmed using rice microsatellite markers. CLXL8 rice flowered 2 to 4 d earlier than CL161 rice, and flowering was completed within 1 wk in all plantings. The flowering duration of most red rice biotypes ranged from 4 to 17 d. Flowering synchrony of red rice biotypes and CL rice ranged from 0 to 100% at different plantings. In general, CLXL8 had greater flowering overlap and higher outcrossing rate with red rice than did CL161 rice. The outcrossing rate of red rice biotypes ranged from 0 to 0.21% and 0 to 1.26% with CL161 and CLXL8 rice, respectively. The outcrossing rate differed within each planting date (P