Abstract:

Gene introgression usually results from spontaneous hybridization among closely related exotic and native species, and thus can significantly impact the genetic structure of native species, especially on endangered species. It is believed that no interspecies reproductive barriers exist within Liriodendronspp. The endangered status of Liriodendron chinense in China is compounded by the potential risk of interspecific introgressive hybridization resulting from the frequent introduction ofL. tulipiferaand by the extensive planting of hybrid Liriodendron within the past decade. Here, we report a possible trend of interspecific introgressive hybridization in the genus Liriodendron. We sampled five mixture plantations with L. chinense, L. tulipifera, and hybrid Liriodendron from southeastern China. In each plantation, 19-130 adults and 60-117 naturally regenerated seedlings or open-pollinated progeny were sampled. The mating pattern of Liriodendron was examined using parentage analysis based on 11 EST-SSR loci, and the extent of introgressive hybridization was estimated in terms of an introgression coefficient derived from parentage-offspring regression coefficients of allele frequencies. We found evidence of interspecific introgressive hybridization in all five plantations of Liriodendron, although the orientation and extent of gene introgression differed among plantations. Furthermore, for any species, we found that the extent of gene introgression was positively related to its population size. Herein, we present conservation strategies for Liriodendron chinense in the context of our results.

Key words: Liriodendron, parentage analysis, introgressive hybridization, introgression coefficient