Many varieties of transgenic rice are under development in countries where
wild and weedy relatives co-occur with the crop. To evaluate possible risks
associated with pollen-mediated transgene dispersal, we conducted a two-year
survey in Vietnam to examine overlapping flowering periods of rice (Oryza sativa L.),
weedy rice (O. sativa), and wild rice (O. rufipogon Griff.), all of which are inter-fertile. We
surveyed populations in two regions of the Mekong Delta, northern and
southern, and at three sites in each of three habitats per region: fresh
water, saline water, and acid sulfate soil. Weedy rice frequently flowered
simultaneously with neighboring cultivated rice plants. Flowering was more
seasonal in wild rice and often peaked in November and December. Peak
flowering times of wild rice overlapped with adjacent rice fields at all of the saline
sites and half of the acid sulfate sites. The longer flowering season of
wild rice ensured that crop-to-wild gene flow was possible in fresh water
habitats as well. Our second objective was to determine whether wild and
weedy rice populations are exposed to pests that could be targeted by future
transgenes, which may then provide fitness benefits. These populations
shared many pathogen and insect herbivore species with cultivated rice
(leaffolder, locust, cricket, planthoppers, rice bug, stem borer, sheath
blight, blast, bacterial leaf blight, and brown spot). Damage by leaffolders
and locusts was the most frequently observed insect feeding damage on all
three rice types. Indicator species analysis revealed that most of the
insect herbivores were associated with particular habitats, demonstrating
the importance of broad geographic sampling for transgenic rice risk
assessment. These survey data and the strong likelihood of gene flow from
cultivated rice suggest that further studies are needed to examine the
effects of transgenic traits such as resistance to pests on the abundance of
wild and weedy rice.