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ARS Home » Southeast Area » Stuttgart, Arkansas » Dale Bumpers National Rice Research Center » Research » Publications at this Location » Publication #232947
Title: Maximum outcrossing rate and genetic compatibility between red rice (Oryza sativa) biotypes and Clearfield™ rice

Author
item SHIVRAIN, VINOD - UNIV. OF AR RREC
item BURGOS, NILDA - UNIV. OF AR
item Gealy, David
item MOLDENHAUER, KAREN - Rice Research And Extension Center
item BAQUIREZA, CECILIA - UNIV. OF AR

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2008
Publication Date: 8/25/2008
Citation: Shivrain, V.K., Burgos, N.R., Gealy, D.R., Moldenhauer, K.K., Baquireza, C.J. 2008. Maximum outcrossing rate and genetic compatibility between red rice (Oryza sativa) biotypes and Clearfield™ rice. Weed Science. 56:807-813. DOI: 10.1614/WS-08-026.1.

Interpretive Summary: Imazethapyr herbicide-resistant rice (ClearfieldTM, CL) systems are now used prominently to control weedy red rice in southern U.S. rice fields. However, the unintended transfer of the herbicide resistance gene from CL rice to red rice is a potential ecological risk. We examined: a) the maximum outcrossing rates between 12 red rice biotypes and CL161 rice detected during the period of flowering overlap in the field and b) the genetic compatibility between 12 red rice biotypes and CL161. To evaluate the flowering overlap between red rice biotypes and CL161 as well as its impact on outcrossing rate, field experiments were conducted at four planting times from early April to late May. The red rice biotypes were planted as a single row bordered by four rows of CL161 on each side. Rice and red rice flowering dates were monitored. Red rice seeds were harvested, screened for resistance to imazethapyr herbicide, and confirmed as true hybrids of red rice and CL161 using DNA markers. The percent seed set on red rice plants that had been manually pollinated using pollen from CL161 rice was used as an estimate of genetic compatibility. Red rice typically had a lengthy flowering duration (5 to 16 days) in contrast to that for CL161 (6 days). Nearly all of the red rice types had greater than or equal to a 70% overlap in flowering time with CL161 for at least one planting date. However, a red rice biotype with only 40% overlap in flowering with CL161 resulted in the highest observed outcrossing rate of 0.25%. The lowest observed outcrossing rate was 0.03%. Manual crosses in the greenhouse resulted in seed sets of 49 to 94%. These experimental results indicate that overlap in flowering as well as genetic compatibility between red rice biotypes and cultivated rice can impact the level of hybridization that occurs in rice farm fields.

Technical Abstract: Although red rice can be selectively controlled with imazethapyr in ClearfieldTM (CL) rice, the transfer of the imazethapyr-resistant gene from CL rice to red rice is an ecological risk. Previous experiments indicated that flowering synchronization and genetic compatibility between cultivated rice and red rice could strongly influence the rate of gene transfer from cultivated rice to red rice and vice versa. Thus, we examined the: a) variability in maximum outcrossing rate between 12 red rice biotypes and CL161 rice detected during their peak flowering overlap in the field and b) genetic compatibility between 12 red rice biotypes and CL161 rice. Experiments were conducted at the Rice Research and Extension Center, Stuttgart and Fayetteville, AR from 2005 to 2007. To evaluate the flowering synchrony of red rice biotypes and CL161 rice as well as its impact on outcrossing rate, field experiments were conducted at four planting times from early April to late May. The red rice biotypes were planted in the middle row of 9-row CL161 plots and flowering was monitored. Red rice seeds were harvested and screened for imazethapyr resistance in subsequent years. Survivors were confirmed as outcrosses between red rice and CL rice using rice SSR markers. The outcrossing rate was calculated based on genetically confirmed hybrids. To determine compatibility, manual crosses were performed between 12 red rice biotypes types and CL161 rice in the greenhouse. Seed set from manual crosses was used as an indicator of compatibility between red rice types and CL161 rice. All red rice types had a protracted flowering duration ranging from 5 to 16 d after the onset of flowering in contrast to 6 d in CL161 rice. Ten of the twelve types of red rice had greater than or equal to a 70% overlap in flowering time with CL161 rice in at least one planting date. The maximum outcrossing rate between red rice biotypes and CL161 ranged from as low as 0.03% to as high as 0.25%. There were significant differences in outcrossing rate between red rice biotypes (P < 0.05). One red rice biotype had 40% overlap in flowering with CL161, which resulted in the highest outcrossing rate of 0.25%. Manual crosses in the greenhouse resulted in seed sets of 49 to 94%. The majority of red rice biotypes had similar compatibility with CL161 rice, but Chi-5 showed less compatibility with CL161 than Gre-5 and Lon-1. This experiment indicates that overlap in flowering and genetic compatibility between red rice biotypes and cultivated rice impact the level of hybridization that can happen in the field.