Evaluating Elite Alfalfa Lines for N2-Fixation Under Field Conditions
The nitrogen (N2) fixation capacity of a legume-Rhizobium symbiosis is associated with several metabolic processes and morphological characteristics of the host and of the bacterium. These processes and characteristics are quantitatively regulated with gene expression often dependent upon the environment in which the symbiosis develops. Because of the close association between gene expression and environment, we must understand how metabolic processes investigated in the artificial and relatively uniform environments of laboratories and glasshouses respond to the uncontrolled environments of the field. This understanding is essential if research to improve N2−fixation of legumes is to impact beneficially on agricultural cropping systems. For this reason, a major thrust of our research program is to conduct field experiments to determine the N2−fixation capabilities of alfalfa (Medicago sativa L.) previously selected in artificial environments for traits associated with N2−fixation. The purpose of this communication is to report three investigations of alfalfa N2−fixation and Rhizobium strain preference using germplasm from our breeding program, and to interpret the results in the context of plant improvement.
KeywordsRhizobium Strain Symbiotic Nitrogen Fixation Isotope Dilution Technique Nodule Occupancy Herbage Yield
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