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ARS Home » Southeast Area » Stuttgart, Arkansas » Dale Bumpers National Rice Research Center » Research » Publications at this Location » Publication #335824
Title: Introgression of Clearfield(TM) rice crop traits into weedy red rice outcrosses

Author
item SINGH, VIJAY - University Of Arkansas
item SINGH, SHILPA - University Of Arkansas
item Black, Howard
item BOYETT, VIRGINIA - University Of Arkansas
item BASU, SUPRATIM - University Of Arkansas
item Gealy, David
item GBUR, EDWARD - University Of Arkansas
item PEREIRA, ANDY - University Of Arkansas
item SCOTT, ROBERT - University Of Arkansas
item CAICEDO, ANA - University Of Massachusetts
item BURGOS, NILDA - University Of Arkansas

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2017
Publication Date: 3/20/2017
Citation: Singh, V., Singh, S., Black, H.L., Boyett, V., Basu, S., Gealy, D.R., Gbur, E.E., Pereira, A., Scott, R.C., Caicedo, A., Burgos, N.R. 2017. Introgression of Clearfield(TM) rice crop traits into weedy red rice outcrosses. Field Crops Research. 207:13-23.

Interpretive Summary: Red rice seeds were obtained from Arkansas farms with a history of growing Clearfield(TM) rice varieties that contain a herbicide resistance (HR) gene. These rice varieties have enabled farmers to control weedy (‘red’) rice and other difficult-to-control grass weeds much better than in the past. However, outcrossing between the Clearfield(TM) rice and red rice plants is threatening the long term viability of Clearfield(TM) rice in some areas. In field and laboratory studies, the red rice seeds from these fields were evaluated to determine the degree to which the HR gene had moved into the red rice populations through outcrossing, their plant characteristics, and the potential impacts of this on weedy red rice management. Outcrossing between Clearfield(TM) rice and red rice was verified using DNA analyses that can differentiate between rice and red rice and identify the presense of the HR gene carried in the Clearfield(TM) rice varieties. Seventy-nine percent of the red rice samples proved to be resistant to the herbicide used with Clearfield(TM) rice. All of the HR red rice plants were shown to possess the specific HR gene that is present in the most popular Clearfield(TM) rice varieties, which proved that the HR red rice plants had picked up the HR gene through outcrossing with Clearfield(TM) rice. The majority of HR red rice plants had moderately low “weed suppressive” abilities and weedy traits compared with common red rice plant types in that they had plant height, plant spreading or shading ability, leaf dimensions, and seed shattering and seed dormancy that were similar to cultivated rice. A small fraction of kernels produced on these “weedy red rice” plants actually produced white-colored seeds, which can be tricky to identify and remove from rice grain. Many of the HR red rice plants had a significant overlap in flowering time with rice, which would allow further outcrossing with Clearfield(TM) rice. The “crop-like” traits observed in many HR red rice plants suggests that they have reduced competitiveness, and therefore could be managed effectively using integrated weed control programs.

Technical Abstract: Studies were conducted to determine the impact of introgression of crop alleles into weedy rice populations. Seeds of 89 weedy rice accessions collected from Arkansas fields in 11 counties, with a history of Clearfield(TM) rice production, were planted in 2011 and treated with two applications of imazethapyr (0.071 kg ai ha-1). Survivors were genotyped using an allele-specific PCR assay to detect the presence of resistance-endowing 'als' mutations, S653N and G654E, in herbicide-resistant (HR) weedy rice that could potentially have originated from Clearfield(TM) cultivars planted in the state. Hybridization between Clearfield(TM) rice and weedy rice was verified using microsatellite markers RM 215, RM 220, RM 234 and RID12. Two to five HR plants per accession per replication (727 plants) representing different plant morphotypes were characterized for 16 morphological and biological traits. Seventy-nine percent of accessions were resistant to imazethapyr. HR weedy rice plants carried the S653N mutation and were confirmed as outcrosses with Clearfield(TM) rice using microsatellite markers. Ten weedy rice accessions (nearly 25% of confirmed outcrosses) harbored multiple alleles from cultivars, indicating previous hybridization events with more than one cultivar or an outcross with weedy rice. The majority of HR weedy rice accessions were similar to cultivated rice in height, culm angle, flag leaf length and width, days to flower, seed shattering and dormancy. Kernels of 20% of the parent weedy rice accessions were segregating for white and red bran color. Two of the parent weedy rice accessions with gold hull were homozygous for white bran and produced progenies with 100% white-bran kernels; thus, weedy rice was no longer exclusively red. A larger fraction of HR weedy rice overlapped in flowering with rice cultivars compared with that of historical weedy rice, and exhibited more crop-like traits than their historical counterparts. Many HR weedy rice accessions exhibited reduced seed shattering and dormancy, indicating that a significant proportion of outcrosses would likely not persist, which potentially would increase the effectiveness of integrated weed management programs.