Annals of Applied Biology ISSN 0003-4746 RESEARCH ARTICLE No effect of transgene and strong wild parent effects on seed dormancy in crop–wild hybrids of rice: implications for transgene persistence in wild populations S.S. Dong 1 , M.Q. Xiao 1 , J. Rong 2 , H. Liao 1 , B.-R. Lu 1 , J.K. Chen 1 & Z.P. Song 1 1 Ministry of Education Key Laboratory for Biodiversity and Ecological Engineering, Institute of Biodiversity Science, Fudan University, Shanghai, 200433 China 2 Plant Ecology and Phytochemistry, Institute of Biology Leiden, Leiden University, PO Box 9505, 2300 RA Leiden, The Netherlands Keywords Crop –wild hybrid; dormancy; germination; rice; seed viability; transgene persistence. Correspondence Z. Song, Ministry of Education Key Laboratory for Biodiversity and Ecological Engineering, Institute of Biodiversity Science, Fudan University, Shanghai, 200433 China. Email: songzp@fudan.edu.cn Received: 25 January 2011; revised version accepted: 9 July 2011. doi:10.1111/j.1744-7348.2011.00504.x Abstract Soil seed banks act as a gene pool for local plant species and, as such, can buffer local populations, especially those experiencing challenging environmental conditions. Seed dormancy has important implications to dynamics of soil seed banks. Therefore, estimating the seed dormancy of transgenic crop–wild hybrids could shed light on the persistence of transgenes in wild-plant soil seed banks. Individuals from eight populations of wild rice Oryza rufipogon were crossed with those of three insect-resistant transgenic rice lines. Selfed (F2 – F4) and backcrossed populations (BC1, BC1F2 and BC1F3) were then made from the hybrids. Seed germination was tested under three treatments: (a) normal; (b) overwintering in soil; and (c) one-week heat-shocking. The effects of trans- gene, wild parent and hybrid generation on hybrid seed germination were examined. No significant effect of insect-resistant transgenes (Bt and CpTI ) was detected on the seed dormancy of crop–wild hybrids, while a significant wild parent effect was found. The seeds of advanced generation hybrids have higher germination percentages and lower dormancy than do those of F1 and BC1 generations. The study showed that the dormancy of hybrid seeds was determined mainly by their genetic backgrounds. All hybrid seeds have higher germination percentages and lower dormancy (and, consequently, a poorer overwintering ability), compared with wild seeds, and reduce dormancy would contribute to a fitness disadvantage, compared with wild types. Therefore, such seeds might form part of naturally occurring soil seed banks, through which crop genes would persist in wild populations. Introduction With the rapid development of biotechnology, increasing numbers of genetically modified (GM) crops have been produced. The global cultivation area of GM crops grew steadily from 1996 and reached 134 million hectares in 2009 (James, 2009). Although GM crops offer new oppor- tunities for improved food security and benefit farmers, there are ecological concerns over whether transgenes could lead to unwanted environmental consequences if they introgressed into wild populations via crop–wild gene flow (Crawley et al., 2001). The possibilities of transgene introgression have been assessed in several crops by estimating crop–crop or crop–wild/weed gene flow (e.g. Burke et al., 2002; Legere, 2005; Wang et al., 2006; Rong et al., 2007; Snow et al., 2010). The general view is that transgene outflow into wild relatives could be common (Guadagnuolo et al., 2006). However, the estimating of transgene introgression is only the first step in assessing the ecological risks of GM crop– wild hybrids. The persistence of transgene in wild population depends on relative fitness of crop – wild hybrid. The transgene may be eliminated from wild population and GM crop–wild hybrids are unlikely to have ecological consequences if 348 Ann Appl Biol 159 (2011) 348 – 357  2011 The Authors Annals of Applied Biology  2011 Association of Applied Biologists