Characteristics of bacteria from oilseed rape in relation to their biocontrol activity against Verticillium dahliae

The potential of bacteria that are adapted to the oilseed rape root environ ment for use in the biological control of Verticillium dahliae, Kleb was in vestigated in both controlled and non-sterile growth conditions. Bacterial strains dominated by the red-pigmented members of enterobacteriaceae were i solated from thoroughly washed and air-dried root segments of symptomless y oung rape plants. Other associated strains found either belonged to Alcalig enes sp., Stenotrophomonas spp. and Pseudomonas spp. (Pseudomonas acidovora ns and Pseudomonas putida) or were unidentified according to fatty acid met hyl ester profile analysis. A total of 19 strains isolated in this study to gether with two previously studied strains, Serratia proteamaculans and Pse udomonas chlororaphis, were characterized on the basis of their interaction s with V. dahliae and a number of functional characteristics. In line with earlier observations with root-colonizing fungi also from oilseed rape, all bacterial strains suppressed the pathogen not only directly and but also i ndirectly in in vitro assays. Mechanisms of suppression were apparently mul tifold among the strains, but production of hydrogen cyanide does not seem to be involved in indirect inhibition. The majority of the strains possesse d the ability to produce cellulases, proteases and phosphatases and some ev en produced chitinases and induced hypersensitive responses, indicating the ir potential for nutrient acquisition as well as colonization capacity and active recognition by the plant cells. Investigations in non-sterile field soil revealed that some strains protected rape plants from V. dahliae partl y by delaying symptom development. None of the strains, however, was strong ly deleterious to rape growth either in the presence or absence of the path ogen. Light microscopic observations of roots and results based on agar pri nting techniques revealed the potential of the studied strains to colonize or interfere with the pathogen colonization. This study provides some insig ht into the evolved relationship of bacterial residents with their host in terms of their potential importance in its fitness.