Improved growth and weed control of glyphosate-tolerant poplars

We studied the impact of glyphosate tolerance on weed control and tree growth in field-grown transgenic poplars. Using Agrobacterium-mediated transformation, we produced 94 transgenic transformation events in four hybrid genotypes (three Populus trichocarpa × P. deltoides and one of P. trichocarpa × P. nigra). These lines were screened for high levels of tolerance in two plantations in Oregon. Based on screening results, we propagated four lines from two hybrid genotypes to study their value for weed control and productivity in a 2-year management trial in eastern Oregon, comparing conventional weed control at the time of the study to methods that included over-the-top applications of glyphosate during the growing season. Herbicide tolerance was stable in all of the trees over the 2-year period. Weed control, based on weed abundance, was substantially improved in the over-the-top application. Growth of the trees, as measured by stem volume index, was correspondingly improved; transgenic trees grew approximately 20 % faster than the transgenic and non-transgenic control trees. An exploratory life-cycle analysis of the embodied greenhouse-gas benefits for a coppice bioenergy plantation suggested that over a 6-year rotation with three coppice cycles, the growth improvement could provide an ~8 % savings in greenhouse gas emissions per unit of wood produced. Despite the potential benefits, adoption of this technology will depend on compatibility with management regimes, regulatory and market acceptance, and probably also the development of a robust transgene containment system.