Characterization of a free-living maize-rhizosphere population of Burkholderia cepacia: effect of seed treatment on disease suppression and growth promotion of maize

Abstract

A Burkholderia cepacia population naturally occurring in the rhizosphere of Zea mays was evaluated by metabolic and molecular profiling and for some traits associated with biocontrol and plant growth promoting (PGP) activity. The purpose was to investigate the potential of this bacterial species closely associated with maize to act as a PGP inoculant. The bacterial strains, isolated on semiselective PCAT medium, were assigned to the species B. cepacia by an analysis of the restriction patterns produced by amplified DNA encoding 16S rRNA (16S rDNA) (ARDRA) with the enzyme AluI. Biodiversity among the 14 B. cepacia isolates was analyzed by the Biolog GN system and by the random amplified polymorphic DNA (RAPD) technique with two 10-mer primers. The analysis of the Biolog data revealed that all rhizosphere B. cepacia strains formed a tight phenetic cluster which includes B. cepacia LMG 11351, a reference strain isolated from the maize rhizosphere, and allowed us to distinguish single isolates from one another. The analysis of RAPD patterns allowed us to identify two principal groups in this bacterial population. Other tests included in vitro inhibition of the maize pathogens Fusarium spp., analysis of siderophore production, bioassay using maize seeds coated with B. cepacia in soil artificially infested with the maize pathogens Fusarium spp., and greenhouse-based plant growth promotion experiments with maize. The data obtained demonstrated that all B. cepacia strains displayed a wide antibiosis against the phytopathogenic fungi studied and produced, under low iron conditions, hydroxamate-like and thiazo-like siderophores. Moreover, the bioassay allowed us 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 effect of seed bacterization with B. cepacia isolates on maize growth depended on the potting medium used. When a sand-peat/manure mixture was used, almost all B. cepacia isolates promoted maize growth ; whereas, when the soil collected from the field of bacterial isolations was used, only four strains exerted a positive effect on maize growth. z

Germinação e vigor de sementes de arroz inoculadas com bactérias diazotróficas

“…Segundo Peng et al (2002) é possível que muitas dessas bactérias associadas às plantas de arroz estejam envolvidas na promoção do crescimento de plantas. A capacidade da população de microrganismos em promover o crescimento de plantas envolve mecanismos como a fixação biológica de nitrogênio, a produção de fito-hormônio e ou a solubilização de fosfato e o aumento na formação de pelos radiculares e, ou, a formação de raízes laterais, a inibição do crescimento de fungos e a indução de resistência sistêmica no hospedeiro (Rodriguez & Fraga, 1999;Bevivino et al, 2005;Compent et al, 2005;Han et al, 2005). Atualmente, alguns estudos têm sido realizados no sentido de avaliar os aspectos benéficos da associação de bactérias diazotróficas com a germinação de sementes.…”

Burkholderia cepacia Complex Bacteria from Clinical and Environmental Sources in Italy: Genomovar Status and Distribution of Traits Related to Virulence and Transmissibility

“…While it has emerged as a human pathogen, B. cepacia has attracted increasing interest in agriculture and biotechnology for its potential as a biocontrol and bioremediation agent. The reasons for this interest include the organism's ability to promote plant growth by antagonizing soilborne plant pathogens (5,6,21,30) and to degrade hydrocarbons and thus assist with the bioremediation of contaminated soil and water (16,23,25 Although all nine species or genomovars have been recovered from CF patients, B. multivorans and B. cepacia genomovar III account for the majority of isolates from CF patients, especially epidemic clones (26,29,35,37). As far as environmental strains are concerned, in the first extensive study performed with bacterial strains isolated from a single habitat (15), B. cepacia genomovar I, B. cepacia genomovar III, and B. ambifaria have been reported to be the most widespread members of the B. cepacia complex in the rhizosphere of maize; moreover, Balandreau et al (2) found that a group of B. cepacia-like organisms isolated from the rhizosphere or tissues of maize, wheat, and lupine belonged to B. cepacia genomovar III.…”

Evaluation of some commercial bacterial biofertilizers and isolates against root knot nematode, Meloidogyne incognita infesting green bean, Phaseolus vulgaris

“…These results on biofertilizers agree with those obtained by other authors. Bevivino et al (1998) found that rhizobacteria could stimulate plant growth either by producing growth hormones and improving nutrient uptake or by changing microbial balance in the rhizosphere of the plants through producing some compounds lethal to nematodes or by modifying the rhizosphere environment (Mishra et al, 1987). Al-Rehiayani et al (1999) found that B. megaterium reduced population densities of M. chitwoodi and Pratylenchus neglectus on potato roots by up to 50%.…”