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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. [ABSTRACT FROM AUTHOR]

Overexpression of genes that modify gibberellin (GA) metabolism and signaling have been previously shown to produce trees with improved biomass production but highly disturbed development. To examine if more subtle types of genetic modification of GA could improve growth rate and modify tree architecture, we transformed a model poplar genotype (Populus tremula × P. alba) with eight genes, including two cisgenes (intact copies of native genes), four intragenes (modified copies of native genes), and two transgenes (from sexually incompatible species), and studied their effects under greenhouse and field conditions. In the greenhouse, four out of the eight tested genes produced a significant and often striking improvement of stem volume, and two constructs significantly modified the proportion of root or shoot biomass. Characterization of GA concentrations in the cisgenic population that had an additional copy of a poplar GA20-oxidase gene showed elevated concentrations of 13-hydroxylated GAs compared to wild-type poplars. In the field, we observed growth improvement for three of the six tested constructs, but it was significantly greater for only one of the constructs, a pRGL:GA20-oxidase intragene. The greenhouse and field responses were highly variable, possibly to due to cross-talk among the GA pathway and other stress response pathways, or due to interactions between the cisgenes and intragenes with highly similar endogenes. Our results indicate that extensive field trials, similar to those required for conventional breeding, will be critical to evaluating the value and pleiotropic effects of GA-modifying genes [ABSTRACT FROM AUTHOR]

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Field trials are widely known to be essential for understanding the value and adaptability of trees produced via conventional and transgenic biotechnologies. However, obtaining permission for transgenic field trials is often considered to be very difficult in many countries. To understand the extent of regulatory requirements around the world and the burdens they impose, we surveyed 36 scientists and practitioners from 20 different countries who had experience or direct knowledge of regulatory compliance with field trials of transgenic trees. Results showed that permits and monitoring were universally required, and that public disclosure of field trial locations was required in three quarters of countries. Other major findings were that: separate approvals for different constructs, tree species, and trial locations were required in more than three quarters of the countries; characterization of each transgene insertion event was required as part of the application in four fifths of countries; and the application process itself was perceived as the largest single burden. Regulatory tiers that differentiate different kinds of transgenic trees based on perceived risk were present in only one fifth of countries. The data confirm the widespread perception among scientists that the costs and burdens of conducting field trials with transgenic trees are nearly universal substantial impediments to scientific and breeding progress. [ABSTRACT FROM AUTHOR]

An abstract of the conference paper "Field trials of GM trees in the USA: Activity and regulatory developments," by Steven H. Strauss and Venkatesh Viswanath is presented.

An abstract of the conference paper "Greenhouse and field evaluation of transgenic poplars with modified gibberellin metabolism and signaling genes," by Venkatesh Viswanath and colleagues is presented.