Gene flow from crops to wild relatives in Asia: case studies and general expectations

摘要

Gene flow is the major pathway for transgene escape from crops to their wild relatives (including weedy biotypes). Alien transgenes that escape to and persist in the environment will probably lead to ecological risks. Those alien genes resistant to biotic and abiotic stresses in particular could significantly enhance ecological fitness of the wild relative species, causing unpredictable environmental disasters. There are several major crop species such as rice, soybean, oilseed rape, bread wheat, and millets grown in Asian countries. These crops have their wild relative species and weedy types available in the agriculture ecosystem. If transgenic varieties of these crops are released into environment, alien transgene escape to wild relatives through outcrossing will likely occur. In the origin and diversity centers of crop species and wild relatives, the possibility of transgene escape to the wild species will be high, and as a consequence, the ecological risks caused by the transgene escape will also be high. It is general understanding that the possible crop-to-wild transgene escape must meet three conditions, these are (ⅰ) spatially, transgenic crops and their wild relatives should have an overlapped distribution and be in close contact; (ⅱ) temporally, the flowering time of transgenic crops and their wild relatives should encounter with each other; and (ⅲ) transgenic crop and the target wild relative species should have sufficiently close biological relationships and non-significant reproductive barriers. This paper presents studies of crop-to-wild gene flow in Asia using rice as an example, and discusses the general expectations of transgenic escape. Our research results on geographic distribution, flowering habit, interspecific hybridization, and gene flow of cultivated rice (Oryza sativa) and its closely related wild relatives, are used to estimate the opportunity of transgene escape to the wild relatives.