Submitted to: Arkansas Crop Protection Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/26/2007
Publication Date: 11/27/2007
Citation: Shivrain, V.K., Burgos, N.R., Sales, M.A., Smith, K.L., Gealy, D.R., Black, H.L. 2007. Effect of Plant and Environmental Factors on ALS-resistant Gene Transfer from ClearfieldTM Rice to Red Rice. Arkansas Crop Protection Association Proceedings 11:19. Interpretive Summary:
Technical Abstract: Imazethapyr-resistant gene from ClearfieldTM (CL) rice varieties transfers through pollen flow to red rice (Oryza sativa L.), a noxious weed in rice production in southern states. Factors which affect gene transfer rate include, but are not limited to, plant and environmental factors. Thus, we aimed to determine the impact of red rice biotypes, CL cultivars, and planting and flowering times of red rice and CL cultivars on the rate of gene transfer. Field experiments were conducted at the Rice Research Extension Center, Stuttgart; Southeast Research and Extension Center, Rowher; and Vegetable sub-station, Kibler, AR from 2005 to 2007. Experimental design was a split-split plot with 3-4 replications. Treatment factors were: planting date (main plot with 4 treatments: early April to late May at 2-week intervals); CL cultivar (subplot with 2 treatments: CL161 and CL hybrid); and red rice biotype (sub-subplot with 12 treatments: 7 strawhull, 3 blackhull, and 2 brownhull). Red rice was planted in the middle row and flanked by four CL161/CL hybrid rice on each side. Emergence, flowering, and plant height of red rice and CL rice were recorded. Red rice seed was harvested at maturity and a sub-sample of 100 g was planted in the field in subsequent years. Red rice seedlings were sprayed twice with imazethapyr at 0.14 kg ai/ha. Red rice plants which survived imazethapyr applications were counted. Leaf tissues from survivors were collected for DNA analysis to confirm outcrossing. Furthermore, in the summer of 2007, manual crosses were performed between the 12 red rice accessions and CL161 to determine their compatibility, using three biological replicates of each accession. In all plantings, there was overlap in flowering (> 50%) between both cultivars and at least six red rice accessions. Interactions between planting date by CL cultivar and planting date by red rice accession were significant (p< 0.05) for outcrossing rate. The outcrossing rate in different red rice accessions varied from 0 to 0.7% in different planting dates. In general, outcrossing was highest with brownhull red rice followed by blackhull and strawhull, and occurred at the first planting date. Outcrossing rate differed between red rice accessions at the same planting date due to differences in their flowering time. Averaged over planting dates, the outcrossing rate between CL hybrid and red rice accessions was 0.3% compared with 0.06% in CL161. In experiments related to compatibility, brownhull, blackhull, and strawhull had 91, 78, and 71% seed set, respectively. Between red rice accessions, seed set ranged from 49 to 100%. Field and greenhouse experiments provide evidence for higher outcrossing between brownhull biotypes and CL cultivars. Among red rice biotypes, brownhull infests the least acreage in Arkansas but the rapid evolution of red rice types necessitates measures to counter their proliferation in CL rice production systems.