Submitted to: Weed Science Society of America Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/15/2006
Publication Date: 1/15/2007
Citation: Shivrain, V.K., Burgos, N.R., Smith, K.L., Gealy, D.R., Black, H.L. 2007. Gene transfer rate from CL rice to diverse red rice biotypes. Weed Science Society of America Meeting Proceedings 47:301. Interpretive Summary:
Technical Abstract: The future and sustainability of ClearfieldTM (CL) technology at the producers’ level will be dictated by various factors. Among many, prominent factors which affect the transfer of ALS-resistant gene from CL rice to red rice are: disparity in red rice biotypes 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 behavior of red rice biotypes and CL rice cultivars with respect to planting dates and 2) to determine outcrossing rate and phenotypes of outcrosses between CL cultivars and various red rice biotypes. The experiments were conducted at the SREC, Rohwer and at the RREC, Stuttgart, AR in 2005 and 2006. Experimental design was split-split plot with four replications. Planting time, CL cultivar, and red rice accessions (RRA) were main, sub, and sub-subplot, respectively. Four plantings in both years were initiated at the beginning of April towards the end of May at two week intervals. CL cultivars, CL161 and hybrid CL-XL8, were planted at 90 and 30 lb/A, respectively. Twelve RRA from 10 counties in Arkansas were used. Each RRA was planted in the middle of 9-row, 15-ft long plots with four rows of rice on both sides. Data on emergence, flowering, and number of survivors were recorded. At maturity, red rice seeds were collected from individual plots to determine outcrossing rate. In 2006, a sub-sample of ~ 3000 seeds from each plot collected in 2005 was planted at SREC. Red rice seedlings were treated with three applications of imazethapyr at 0.14 kg ai/ha. Leaf tissues were collected from survivors for DNA extraction. SSR Primers RM 253 and 234 were used to confirm the hybrids. Outcrossing rate was calculated based on the confirmed hybrids. Red rice emergence varied from 10 to 35 days after planting across planting dates. Early planted CL rice and red rice biotypes took longer to flower than those planted later. Flowering period of RRA ranged from 88 to 128, 87 to 117, 79 to 118, and 71 to 116 DAP, in the first, second, third, and fourth planting, respectively. On average, CL-XL8 flowered 3 to 5 days earlier than CL161, although flowering was over within a week in both CL cultivars regardless of planting date. In all plantings, there was 50% synchronization in flowering between both CL cultivars in at least six RRA. Outcrossing rate based on various RRA and planting date varied from ~ 0 to 3%. Higher outcrossing frequency was observed in earlier plantings. However, late flowering accessions had higher outcrossing in later plantings. Number of outcrosses produced is variable among accessions in the same planting date. In general, CL-XL8 had higher outcrossing rate in all planning dates compared to CL161. Phenotype of outcross is affected by CL parent as well as red rice parent. Outcrosses between CL161 and a particular type of RRA are phenotypically uniform. On the other hand, outcrosses between CL-XL8 and an RRA phenotypically segregated in terms of flowering time, height and other various plant characteristics.