Characterization of competitive interactions in the coexistence of Bt-transgenic and conventional rice.
BACKGROUND
Transgene flow through pollen and seeds leads to transgenic volunteers and feral populations in the nature, and consumer choice and economic incentives determine whether transgenic crops will be cultivated in the field. Transgenic and non-transgenic plants are likely to coexist in the field and natural habitats, but their competitive interactions are not well understood.


METHODS
Field experiments were conducted in an agricultural ecosystem with insecticide spraying and a natural ecosystem, using Bt-transgenic rice (Oryza sativa) and its non-transgenic counterpart in pure and mixed stands with a replacement series.


RESULTS
Insect damage and competition significantly decreased plant growth and reproduction under the coexistence of transgenic and conventional rice. Insect-resistant transgenic rice was not competitively superior to its counterpart under different densities in both agricultural and natural ecosystems, irrespective of insect infection. Fitness cost due to Bt-transgene expression occurred only in an agroecosystem, where the population yield decreased with increasing percentage of transgenic rice. The population yield fluctuated in a natural ecosystem, with slight differences among pure and mixed stands under plant competition or insect pressure. The presence of Chilo suppressalis infection increased the number of non-target insects.


CONCLUSIONS
Plant growth and reproduction patterns, relative competition ability and population yield indicate that Bt-transgenic and non-transgenic rice can coexist in agroecosystems, whereas in more natural habitats, transgenic rice is likely to outcompete non-transgenic rice.
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China. liu.yongbo@yahoo.com.
Yongbo
Y
Liu
State Key Laboratory of Integrated Management of Pest and Rodents, Institute of Zoology, the Chinese Academy of Sciences, 8 Dayangfang, Beijing, 100101, China. gef@ioz.ac.cn.
Feng
F
Ge
Institute of Plant Protection, Jiangxi Academy of Agricultural Sciences, Nanchang, 330200, China. lyuyiong@163.com.
Yuyong
Y
Liang
Hubei Insect Resources Utilization and Sustainable Pest Management Key Laboratory, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China. wugang1976@163.com.
Gang
G
Wu
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China. lijsh@craes.org.cn.
Junsheng
J
Li
D018533:Biomass; D018556:Crops, Agricultural / Q000235:genetics / Q000502:physiology*; D017753:Ecosystem; D056084:Genetic Fitness / Q000502:physiology*; D012275:Oryza / Q000235:genetics / Q000502:physiology*; D010572:Pest Control, Biological; D030821:Plants, Genetically Modified / Q000235:genetics / Q000502:physiology*; D012639:Seeds / Q000502:physiology