ENHANCING CROP LEGUME N-2 FIXATION THROUGH SELECTION AND BREEDING

Legume N-2 fixation is variable, but nonetheless is a valuable process in world agriculture. There is great potential to increase the contri bution by the crop legumes to the world's supply of soil N. This will be achieved by (i) increasing the area of legumes sown by farmers; (ii ) improved management of the crops in order that the major determinant s of productivity, e.g. land area, water availability, are converted t o harvested product with maximum efficiency; and (iii) genetic modific ation of the commonly-grown species to ensure high dependence of the l egume crop on N-2 fixation at all levels of productivity. Currently-us ed methods for measuring N-2 fixation and for assessing heritability a nd repeatability of N-2 fixation in breeding and selection programs ar e reviewed. Results from research programs to define genetic variation in N-2 fixation and to enhance N-2 fixation through selection and bre eding are presented with particular emphasis on common bean (Phaseolus vulgaris) and soybean (Glycine max).