Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/15/2008
Publication Date: 3/1/2008
Citation: Shivrain, V.K., Burgos, N.R., Smith, K.L., Gealy, D.R. 2008. Gene flow from weedy rice populations to cultivated rice varies by plant type. In: Proceedings of the 32nd Rice Technical Working Group Meetings, February 18-21, 2008, San Diego, CA. 2008. CDROM. Interpretive Summary:
Technical Abstract: Gene transfer from crops to its weedy and/or wild relatives has been the research focal point during the last decade. Little is known about the rate and consequences of gene transfer from wild or weedy relatives to the cultivated crops. Red rice, a weed which infests ~ 40% of rice acreage in the southern U.S. outcrosses with cultivated rice. Our objectives were to quantify the gene flow rate from different types of red rice (male) to cultivated rice (female) and consequently determine the morphology and fitness of resulting F1 outcrosses. Field experiments were conducted at Stuttgart and Rowher, AR in 2006 and 2007. Experiments were laid out in a randomized complete block design with 3-4 replications. Twelve red rice accessions (7 strawhull, 3 blackhull, 2 brownhull) and ClearfieldTM rice cultivar CL161 were used. Twenty five seeds of an individual red rice accession were planted in the middle row of a 9-row, 5-m long plot, flanked by four rows of CL161 on both sides. Flowering times of red rice and CL161 rice were recorded. At maturity, one row of CL161 on both sides of red rice was harvested, and a sub-sample of 100 g was planted in the field in the subsequent year. Outcrosses resulting from gene transfer from red rice to CL161 were confirmed by DNA analysis. Flowering time, plant height, tiller number, seed production and seed viability were evaluated in the F1 plants. Gene flow rate varied between the two locations, but the trends of outcrossing rate between CL161 and different red rice types were similar. The highest outcrossing rate (0.2 and 0.06% at Stuttgart and Rohwer, respectively) was observed between CL161 and Phi-1 accession, which was strawhull. Whereas, the lowest outcrossing rate (0.01%) at both locations occurred between CL161 and Poi-1 accession, which was blackhull. Outcrossing rate varied between and within hull color of red rice accessions that flowered at the same time. In general, the highest outcrossing was observed with brownhull red rice followed by blackhull and strawhull. F1 outcrosses between CL161 and all red rice types were uniform in height (145±5 cm). These outcrosses were taller than CL161 parent and as tall as or taller than their respective red rice parents. All outcrosses had more tillers compared with CL161 parent; however only 50% of outcrosses had more tillers than their respective red rice parent. The flowering of outcrosses was delayed by two to three weeks compared with CL161 parent. Seventy percent of the total outcrosses produced seeds equal to the red rice parent and 40 to 50% higher than the CL161 rice parent. Seeds of all the outcrosses were red, pubescent, and shattered at maturity. Seed germination of all the outcrosses was >90%. Gene flow from weedy rice populations to cultivated rice varies by pollen donor plant and it can produce populations of outcrosses with higher fitness than cultivated rice. This study indicates that strategies for gene flow mitigation from weeds to crops are equally important as gene flow from crops to weeds.