NEIGHBORHOOD EFFECT OF GENOTYPES OF RHIZOBIUM-LEGUMINOSARUM BIOVAR TRIFOLII, TRIFOLIUM-REPENS AND LOLIUM-PERENNE

Ryegrass, white clover and Rhizobium isolated from the corresponding c lover nodules, were harvested from a natural pasture in the Massif Cen tral mountains (France). The specificity between Lolium, Trifolium and Rhizobium, and the genetic diversity of Rhizobium were examined. This study showed that: 1) Natural neighbouring combinations of white clov er and ryegrass, re-planted together in pots, accumulated a higher bio mass than non-neighbouring ones. This increase of mass is higher in th e presence of the native strain of Rhizobium. 2) When white clover was inoculated with a mixture of Rhizobium strains, nodules were more oft en formed by its native strain. 3) The genetical diversity of the Rhiz obium leguminosarum biovar trifolii was very high, as revealed by elec trophoresis of esterases on seven substrates. These results support th e hypothesis that there is a coadaptation between white clover, ryegra ss and Rhizobium.