Genetic diversity of rhizobia from Leucaena leucocephala nodules in Mexican soils

Leucaena species are leguminous plants native to Mexico. Using two L. leuco cephala cultivars grown in different soils, we obtained 150 isolates from t he nodules. Twelve rDNA types were identified which clustered into groups c orresponding to Mesorhizobium, Rhizobium, and Sinorhizobium by restriction fragment length polymorphism (RFLP) of amplified 16S rRNA genes. Types 2, 4 , 5, 6, 10, 11, and 12 were distinct from all the defined species. Others h ad patterns indistinguishable from some recognized species. Most of the iso lates corresponded to Sinorhizobium 12. Forty-one electrophoretic types (ET s) were identified among the isolates based on the different combinations o f electrophoretic patterns of 13 metabolic enzymes. ETs were clustered into groups in general agreement with the rDNA types. Diverse plasmid patterns were obtained among the isolates, but common plasmids were observed among m ost isolates within rDNA types 5, 10, and 11. The symbiotic plasmids were i dentified among most of the isolates, except for the Mesorhizobium isolates . The affinities of host cultivars for different rhizobial groups and the i mpact of sail cultivation an the soil populations of rhizobia were analysed from the estimation of isolation frequencies and diversity. The results sh owed differences in rhizobial populations in cultivated and uncultivated so ils and also differences in rhizobia trapped by L. leucocephala cv. Cunning ham or Peruvian.