|Shivrain, V - UNIVERSITY OF ARKANSAS|
|Burgos, N - UNIVERSITY OF ARKANSAS|
|Smith, K - UNIVERSITY OF ARKANSAS|
Submitted to: Weed Science Society of America Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 15, 2006
Publication Date: January 15, 2007
Citation: Shivrain, V.K., Burgos, N.R., Smith, K.L., Gealy, D.R., Black, H.L. 2007. Factors influencing ALS-resistant gene transfer from CL (tm) rice to red rice.. Weed Science Society of America Meeting Proceedings. 60:172. Technical Abstract: Red rice (Oryza sativa L.) is hard to control due to its genetic similarity to cultivated rice. Herbicide-resistant Clearfield ™ (CL) rice now offers an excellent option for red rice control. However, sustainability of CL technology at the producers’ level will be dictated by various factors. Prominent factors that affect the transfer of the ALS-resistant gene from CL rice to red rice are: disparity in red rice and CL cultivars; flowering time of red rice and CL cultivars; and planting time. Our objectives in this experiment were to 1) evaluate the flowering pattern of red rice accessions from AR and two CL cultivars; 2) determine the outcrossing rate between CL cultivars and red rice accessions at four planting dates; and 3) characterize the phenotypes of outcrosses between CL cultivars and red rice types. The experiments were conducted at the Rice Research and Extension Center, Stuttgart and at the Southeast Research and Extension Center, Rohwer, AR, in 2005 and 2006. The experimental design was a split-split plot with three replications. Planting time, CL cultivar, and red rice accessions were main, sub-, and sub-subplot, respectively. There were four plantings in 2005, from April 16 until the end of May at two-week intervals. Twelve red rice accessions from 10 counties in AR were used. The accessions represent an assortment of characteristics: short and tall, awned and awnless, and early and late flowering. Each red rice accession was planted in the middle of 9-row, 15 ft. long plots with four rows of rice (CL161 or CLXL-8) on both sides. Data on emergence and flowering were recorded. At maturity, red rice seeds were collected to determine outcrossing rate. In 2006, a sub-sample of approximately 3,000 seeds from each plot was planted at Rohwer. Red rice seedlings were treated with three applications of imazethapry at 0.14 kg ai/ha, starting at the V2 stage. Leaf tissues were collected from survivors for DNA analysis and SSR primers RM 253 and 234 were used to confirm the outcrosses. Outcrossing rate was calculated based on the number of confirmed hybrids. Outcrosses were grown until the end of the season and characterized morphologically. CL rice and red rice accessions planted earlier took relatively more days to flower than those planted later. The flowering period of red rice accessions ranged from 88 to 128, 87 to 117, 79 to 118, and 71 to 116 days after planting in the first, second, third, and fourth planting, respectively. On average, CLXL-8 flowered 3 to 5 days earlier than CL 161, although flowering was completed within a week in all plantings in both cultivars. In all plantings, there was synchronization in flowering (50%) between both cultivars and at least six red rice accessions. Outcrossing rate of CL cultivars varied form 0 to 1.55% depending on red rice accessions and planting date. Planting date by CL cultivar and planting date by red rice accession interactions were significant (P<0.05) for outcrossing rate. However, no interaction was detected between CL cultivars and red rice accessions for outcrossing rate, implying that the same red rice accession produced more outcrosses regardless of CL cultivars. In general, higher outcrossing was observed with the brownhull type compared with the blackhull and strawhull types. The outcrossing rate differed among red rice accessions in the same planting date. In general, CLXL-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 and the majority (65%) were late in flowering and did not mature in the field. In contrast, outcrosses between CLXL-8 and red rice accessions segregated in terms of flowering time, height, and various other plant characteristics; moreover, about 50% flowered and matured in the field. This experiment demonstrates that outcrossing rate is influenced by CL cultivars, red rice type, and planting time. Hence, outcrossing mitigation and red rice management strategies need to consider these factors.