Rate of transgene spread via long-distance seed dispersal in Pinus taeda

Ecological risk analysis for transgenic conifers is more complex compared to transgenic food crops. With added age and size, greater quantities of seed and pollen travel even farther via long-distance dispersal. Perennial reproduction in conifers means that the same plant disperses annually for one or more decades prior to harvest. Although complex, gene flow in transgenic trees will have adverse consequences only if the following conditions are met: (1) the inserted gene or DNA construct itself inflicts harm or (2) the DNA insertion event causes unintended or secondary effects on fitness traits. Here, transgene seed escape into less managed ecosystems was modeled across 5 and 50 generations using Pinus taeda, an indigenous US timber commodity species. The inserted DNA construct itself was assumed to exert no direct effects on fitness but rather caused secondary or unintended effects on one or more fitness traits. The deterministic population genetics model, based on one or two fitness components, predicted the transgene allele frequency for a single colony of escaped transgenic seedlings through time. The first scenario modeled commercial transgenic plantations. A transgene allele escaping from a 100-ha plantation spread rapidly through time even if it exerted slight, unintended secondary effects on viability and fecundity. The second scenario modeled the case of a 10-ha field trial surrounded by non-transgenic or wild-type forests. Here, transgene spread was slowed by dilution from non-transgenic sources.