Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 2/29/2004
Publication Date: 2/1/2005
Citation: Burgos, N.R., Shivrain, V.K., Rajguru, S.N., Sparks, O.C., Moldenhauer, K.A., Anders, M.M., Gealy, D.R. 2005. Considerations for managing gene flow from Clearfield rice to red rice. Rice Technical Working Group Meeting Proceedings. Abstract. p. 179-180. Interpretive Summary:
Technical Abstract: Gene transfer from rice to red rice is affected by several factors among which are rice cultivar, red rice biotype, spatial separation, and environmental conditions. Effective red rice management has been made possible by Clearfield rice technology. The sustainability of this system hinges upon mitigation of gene transfer from Clearfield rice to red rice. Studies have been conducted at the Rice Research and Extension Center (RREC), Stuttgart, AR to determine effective distance of pollen flow and the effects of planting date and Clearfield cultivar on incidence of outcrossing. Clearfield cultivars CL 121 and CL161 were seeded at 112 kg/ha in circles 10 m in diameter on April 25 and May 21, 2002. Each of these plots were located at the center of a 20-m-diameter circle, which has natural population of Stuttgart strawhull red rice. At each planting date, the cultivars were replicated three times. At grain filling, Clearfield panicles were removed from the inner circle. At maturity, red rice panicles were collected at 0, 0.5, 1, 2, 3, 4, and 5 m from the edge of the inner circle. The remaining red rice was allowed to shatter. Plots were left undisturbed throughout the winter and red rice plants that emerged in 2003 were sprayed with Newpath at 0.07 kg ai/ha three times. The density of red rice and number of survivors were recorded. Leaf tissues were collected from the survivors for DNA analysis. Confirmation of F1 hybrids was done using simple sequence repeat primer (RM180). Genomic DNA was extracted from leaf tissues and used as template for the polymerase chain reaction (PCR) using the SSR primer. Amplified DNA fragments were separated by electrophoresis in a polyacrylamide gel. The gel was stained with Sybr Green and photographed using a Kodak 290 digital camera. Primer RM180 produced one band that was polymorphic between Clearfield rice and red rice. Hybrids produced two bands. The May 21 planting date produced 48 and 39 resistant red rice hybrids, respectively for CL161 and CL121. On average, CL161 produced more outcrosses than CL121 in the later planting date. DNA analysis of April survivors and those from hand-collected samples is on-going. Clearfield cultivars (CL161 and CL121) and Stuttgart strawhull red rice were planted weekly between April 15 and May 19. Red rice was seeded between two rows of Clearfield rice. Flowering was monitored. At grain filling, panicles of red rice were bagged and harvested at maturity. Seeds collected will be screened for resistance to Newpathâ in 2004 and survivors will be tested for hybridization. For the planting dates of April 15 to May 6, CL161 did not flower at the same time with strawhull red rice. Later plantings overlapped in flowering time with strawhull red rice. CL121 flowered earlier than CL161, coinciding with the flowering period of red rice. When planted on April 15, CL121 had minimum overlap in flowering with red rice; however, subsequent planting dates showed increased synchrony in flowering of CL121 and Stuttgart strawhull red rice. To minimize the incidence of outcrossing, it is important to know the flowering times of red rice and Clearfield rice relative to major planting periods. Ditches and areas surrounding fields planted to Clearfield rice should be kept free of red rice since pollen can move within 6 m from the source at least. A related study has shown rice pollen to move more than 25 m.