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Work with plant species of agricultural and horticultural importance indicates that some endophytic bacterial strains stimulate host plant growth by acting as biocontrol agents, either through direct antagonism of microbial pathogens or by inducing systemic resistance to disease-causing organisms. Other endophytic bacterial strains may protect crops from plant parasitic nematodes and insects. In Brazil, the nitrogen-fixing bacterial endophytes of sugarcane, Acetobacter diazotrophicus and Herbaspirillum spp. colonize internal root, stem and leaf tissues, and are thought to provide up to 80% of the host plant's nitrogen requirement. Other endophytic bacteria stimulate plant growth through mechanisms yet to be elucidated. In contrast to agricultural crop species, almost nothing is known about bacterial endophytes of trees. Lodgepole pine (Pinus contorta var. latifolia) and white × Engelmann hybrid spruce (Picea …