Development of glyphosate-tolerant hybrid cottonwoods

High levels of weed control in young cottonwood plantations are required to assure survival and rapid growth. Herbicide-tolerant trees should enhance the efficacy and cost-effectivness of weed control, increasing the profitab ility of cottonwood fiber farming. Using Agrobacterium-mediated transformat ion and indirect shoot organogenesis, we produced 79 lines of transgenic po plars that contain glyphosate tolerance genes. Results indicate high levels of tolerance to Roundup(R) in a substantial number of these lines. When Ro undup Pro(TM) was sprayed at a rate of 4.7-9.4 L/ha (2-4 qt/acre), only min or adverse effects on growth were detected in the highly tolerant lines dur ing the first year of growth.