SPECIFICITY OF RHIZOBIAL STRAINS FOR EFFECTIVE N-2 FIXATION IN THE GENUS LEUCAENA

Twenty-seven accessions of Leucaena, representing 19 species, were ass essed for effective N-fixing symbioses in association with 13 strains of Rhizobium (derived primarily from Leucaena spp. hosts) in N-free co nditions in a glasshouse experiment. Two major leucaena accession grou ps were identified using pattern analysis. Fifteen of the 27 accession s of Leucaena associated with a wide range of rhizobial strains and on ly 4 accessions appeared to have specific rhizobial strain requirement s for effective nitrogen fixation. Nine of the 13 strains of Rhizobium formed highly effective associations with most accessions of Leucaena and only 1 strain (CB3299) was ineffective for N-2 fixation with all accessions. Rhizobial strains CB3126, NGR8 and CB3060 were the most br oadly effective, associating highly effectively with 22, 17 and 21 acc essions of Leucaena, respectively. Accessions of Leucaena were grouped according to rhizobial strain effectiveness, but biological character s such as native range, ploidy level and chromosome number correlated poorly with accession groups.