Integrated approach to nitrogen fixing tree germplasm development

Abstract

The performance of nitrogen fixing trees introduced to new environments depends on proper reconstitution of the symbiotic associations on which the trees rely for their nutrition. Thus selection strategies employed to identify adapted germplasm for particular sites must provide for three-way selection of seed, rhizobia and mycorrhizae. Selected lines must then be multiplied before they can be deployed in varying types of development programs. Special problems are faced in accomplishing these ends with virtually all nitrogen fixing trees. Results and experiences are described which emphasize the importance of parallel selection of plant germplasm and Rhizobium strains. In the case of VA mycorrhuzae, effective symbioses can occur without specific inoculation. Methods for selecting and multiplying trees and their microsymbionts on a large scale are described and discussed.