Growth promotion of common bean (Phaseolus vulgaris L.) by a strain of Burkholderia cepacia under growth chamber conditions

We isolated a strain of Burkholderia cepacia (SAOCV2), which solubilizes in organic phosphates and antagonizes Fusarium oxysporum f. sp. phaseoli and F usarium solani in vitro, from soil. However, this strain does not have anti biotic activity against the bacteria tested in this study, which included b acterial plant pathogens and rhizobia. The efficacy of this strain to enhan ce the growth and P content in common bean was assessed in a soil tradition ally cultivated with this species. In this soil, the common bean is affecte d by Fusarium. Our results show that the strain SAOCV2 was able to mobilize P efficiently in the common bean, so that its P content was increased by 4 4% with respect to uninoculated plants, whereas it was not significantly di fferent with respect to the plants treated with fungicide. Also, the N cont ent in plants inoculated with the strain SAOCV2 was significantly higher th an in uninoculated plants. This result is correlated with a larger number o f nodules in plants inoculated with SAOCV2 and in plants treated with fungi cide and indicates that the inhibition of fungal growth enhances the bacter ial community in the plant rhizosphere, including rhizobia. Our results sug gest that the inoculation with strain SAOCV2 promotes the growth of common bean by several mechanisms, that include P mobilization, antagonism towards pathogenic species of Fusarium and, indirectly, by an increase in nodulati on that may lead to an increase in N-2 fixation. (C) 2001 Elsevier Science Ltd. All rights reserved.