The present invention relates to new methods of selecting and breeding organisms, in particular organisms which exhibit symbiotic behaviour with symbionts, and to new organisms and symbiota developed thereby, such as plant or grass and endophyte symbiota. Multiple symbionts are deployed in multiple organisms and selected for improved symbiotic compatibility and performance early in the breeding process. Methods include producing improved organisms from germplasm, by inoculating host organism germplasm libraries with symbionts selected from symbiont libraries and selecting improved host organisms exhibiting desired symbiota characteristics, and selection of organism-symbiont associations with a desired genetic and metabolic profile by metagenomic analysis of nucleic acid libraries from an organism or organism-symbiont association.
