SEEDS OF PHASEOLUS-VULGARIS BEAN CARRY RHIZOBIUM-ETLI

The presence of soil bacteria on seeds could provide an explanation fo r bacterial geographical spread. We report that Phaseolus vulgaris bea n seeds naturally carry rhizobia on their testa. One hundred eighteen Rhizobium isolates from L-3-1-1-1 seeds were characterized by multiloc us enzyme electrophoresis and compared to Rhizobium species which form nitrogen fixing nodules on the roots of bean plants. As a result of t his and other analyses, seed isolates were classified as R. etli. Seed borne rhizobia are probably moisture limited and are acquired from co ntaminating soil during the harvesting process as seeds from non-opene d pods do not carry them. Rhizobia on seeds are in a presumably desicc ated or dormant state as they require a rehydration process during whi ch they are antibiotic sensitive. With an improved procedure to detect rhizobia on seeds, we found that 5 out of 13 Phaseolus vulgaris bean cultivars tested harbor rhizobia on the seeds. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.