IMPACTS OF WEEDS AND PHYSIOLOGICAL STRESSES IN RICE
Location: Dale Bumpers National Rice Research Center
Title: Outcrossing frequency and phenotypes of outcrosses based on flowering of red rice accessions and Clearfield cultivars in the Grand Prairie
Submitted to: Agricultural Experiment Station Publication
Publication Type: Experiment Station
Publication Acceptance Date: July 6, 2007
Publication Date: August 8, 2007
Citation: Shivrain, V.K., Burgos, N.R., Bullington, J.A., Gealy, D.R., Black, H.L. 2007. Outcrossing frequency and phenotypes of outcrosses based on flowering of red rice accessions and Clearfield cultivars in the Grand Prairie. Agricultural Experiment Station Research Series 550:237-244.
Outcrossing between Clearfield (CL) cultivars and red rice (RR) has been documented in experimental plots as well as in fields. The authors hypothesize that CL cultivars, red rice type, planting time, and flowering time of CL and RR influence the transfer of imazethapyr-resistance genes from CL rice to RR. Our objectives were to 1) evaluate the flowering behavior of RR accessions and CL rice cultivars with respoect to planting dates, 2) determine outcrossing rates between CL cultivars and RR accessions, and 3) determine the phenotypes of outcrosses.
The experiments were conducted at the Rice Research and Extension Center (RREC), Stuttgart, and Southeast Research and Extension Center (SEREC), Rohwer, AR, in the summers of 2005 and 2006. The experimental design was a split-split plot with three replications. Planting time (4), CL cultivar (2), and RR accessions (12) were main-, sub-, and sub-sub-plot, respectively. Each RR accession was planted in the middle of 9-row, 10-ft. long plots with four rows of CL rice on both sides. Red rice seeds were collected in 2005 from individual plots for outcrossing rate determination. Seeds collected in 2005 were planted in the summer of 2006. Red rice seedlings at 2-lf stage were sprayed with imazethapry. Survivors of imazethapyr applications were characterized morphologically at maturity. Leaf tissues were also collected from survivors for confirmatory test of outcrossing by DNA analysis.
Earlier-planted RR accessions and CL rice took longer to flower than later-planted ones. Flowering period of RR accessions ranged from 83 to 114, 83 to 110, 70 to 100, and 70 to 94 days after planting (DAP), in the first, second, third, and fourth plantings, respectively. On average, 'CL XL-8' flowered 3 to 5 days earlier than 'CL 161' although flowering was completed within a week in all plantings in both cultivars. CL XL-8 had a higher outcrossing rate in all planting dates compared with CL 161. Outcrosses between CL 161 and red rice accessions were phenotypically uniform. In contrast, outcrosses between CL XL-8 and red rice accessions segragated in terms of flowering time, height, and various other plant characteristics.