CHARACTERIZATION OF A FREE-LIVING MAIZE-RHIZOSPHERE POPULATION OF BURKHOLDERIA-CEPACIA - EFFECT OF SEED TREATMENT ON DISEASE SUPPRESSION AND GROWTH PROMOTION OF MAIZE

A Burkholderia cepacia population naturally occurring in the rhizosphe re of Zea mays was evaluated by metabolic and molecular profiling and for some traits associated with biocontrol and plant growth promotings (PGP) activity. The purpose was to investigate the potential of this bacterial species closely associated with maize to act as a PGP inocul ant. The bacterial strains, isolated on semiselective PCAT medium, wer e assigned to the species B. cepacia by an analysis of the restriction patterns produced by amplified DNA encoding 16S rRNA (16S rDNA) (ARDR A) with the enzyme AluI. Biodiversity among the 14 B, cepacia isolates was analyzed by the Biolog GN system and by the random amplified poly morphic DNA (RAPD) technique with two 10-mer primers. The analysis of the Biolog data revealed that all rhizosphere B. cepacia strains forme d a tight phenetic cluster which includes B. cepacia LMG 11351, a refe rence strain isolated from the maize rhizosphere, and allowed us to di stinguish single isolates from one another. The analysis of RAPD patte rns allowed us to identify two principal groups in this bacterial popu lation. Other tests included in vitro inhibition of the maize pathogen s Fusarium spp., analysis of siderophore production, bioassay using ma ize seeds coated with B. cepacia in soil artificially infested with th e maize pathogens Fusarium spp., and greenhouse-based plant growth pro motion experiments with maize. The data obtained demonstrated that all B. cepacia strains displayed a wide antibiosis against the phytopatho genic fungi studied and produced, under low iron conditions, hydroxama te-like and thiazo-like siderophores. Moreover, the bioassay allowed u s to select six and eight B. cepacia strains with a potential for the biological control of F. proliferatum ITEM-381 and F. moniliforme ITEM -504, respectively. Growth promotion experiments showed that the effec t of seed bacterization with B. cepacia isolates on maize growth depen ded on the potting medium used. When a sand-peat/manure mixture was us ed, almost all B. cepacia isolates promoted maize growth; whereas, whe n the soil collected from the field of bacterial isolations was used, only four strains exerted a positive effect on maize growth. (C) 1998 Federation of European Microbiological Societies. Published by Elsevie r Science B.V. All rights reserved.