Importance of host plants for detecting the population diversity of Rhizobium leguminosarum biovar viciae in soil

Rhizobium leguminosarum bv. viciae was isolated over 3 y from legumes nodulated with dilutions of soils from arable fields and uncultivated roadside verge sites, and from nodules of resident host legumes when present at these sites. Isolates were characterised by RAPD-PCR confirmed with plasmid profiles. There were large variations in diversity between sites, but diversity was not affected by cultivation per se. Most sites showed very high diversity of RAPD profiles with few profiles being isolated on more than one occasion. However, all profiles of isolates from one site were identical in the first year, but the same profile was not found in the following 2 y.Profiles were not randomly distributed among individual plants or among host species. Different trap plants were usually nodulated by different profiles, suggesting that studies to examine diversity should use large numbers of trap plants and the isolation of rhizobia from few nodules per plant.