Genetic variability of rhizobacteria from wild populations of four Lupinusspecies based on PCR-RAPDs

The metabolic capacities of rhizosphere bacteria can depend on intraspecifi c genetic variability at strain level. We sampled bacteria from the rhizosp here of three populations of four different Lupinus species at two growth s tages (flowering: GS1 and fruiting: GS2). Isolates were identified to the g enus level by classical biochemical tests. The most abundant genera found w ere Bacillus, Aureobacterium, Cellulomonas. Pseudomonas, and Arthrobacter. Genetic divergence of rhizobacteria was tested by PCR-RAPDs. The genetic di stances were low, with mean values of 37 % for Bacillus, 25 % for Aureobact erium, 46 % for Cellulomonas, 16 % for Pseudomonas, and 23% for Arthrobacte r. Aureobacterium, the most abundant genus, predominated in the rhizosphere of all populations and at both growth stages (GS1 and GS2) of L. angustifo lius. The Aureobacterium strains consisted of 11 groups with 90 % similarit y indexes. The cluster analysis of these groups shows that strains isolated from different lupin species and sampling times have extraordinary low div ersity indexes, or are even identical. This fact, together with the low gen etic distance detected in the rhizosphere, reveals a clear specificity in t he plant-bacteria interaction. This specificity could be related with sever al aspects of plant physiology.