Abstract: A novel agriculturally useful composition that includes a seed treated with a selected infectivity-cured Hr plasmid-bearing microorganism. Also provided are methods of enhancing root elongation, shoot elongation or root development of selected seeds. These methods include treating a selected seed with the infectivity-cured Hr plasmid-bearing microorganism. In addition, there is provided a method of inducing germination of Kentucky bluegrass seed that involves treating Kentucky bluegrass seed with a selected infectivity-cured Hr plasmid-bearing microorganism. Furthermore, there is provided a method of promoting plant growth at a lower soil temperature than is common at the time of planting a seed of the plant. Additionally, there is disclosed an inoculant for increasing nodulation, root mass and shoot mass in a leguminous plant. The inoculant contains a Rhizobium microorganism and a selected infectivity-cured Hr plasmid-bearing microorganism.