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Plants growth promoting bacteria (PGPB) are capable of increasing directly or indirectly crop yield. Burkholderia and Pseudomonas have been found in large populations, which inhabit in the rhizosphere of several agriculture crops. The aim of this study was to determine the antagonistic activity in vitro and in vivo of Cuban native plant growth promoting rhizobacteria against Fusarium verticillioides M1, and to assess their ability to produce IAA and to promote plant growth. The bacterial strains were tested to assess their fungal growth inhibition and plant growth stimulation. The plant growth assays were done in a modified microcosm experiment and in greenhouse conditions. The results demonstrated that these rhizobacteria produce IAA and exhibit antagonistic effect on F. verticillioides M1 inoculated in the substrate. Burkholderia sp. MBf21, MBp1, MBf15 and Pseudomonas fluorescens MPp4 stood out for their plant growth stimulation in maize and for the biological control exerted on F. verticillioides M1. The strains Burkholderia sp. MBf21 and MBf15 showed the best results in disease suppression, which was achieved up to 80%. These results have practical relevance, since potentially effective bacterial strains were selected and could be used in agriculture, for the enhancement of plant growth and disease control in maize crop.

Aim: To isolate and characterize rhizobacteria from Theobroma cacao with antagonistic activity against Phytophthora palmivora, the causal agent of the black pod rot, which is one of the most important diseases of T. cacao. Methods and Results: Among 127 rhizobacteria isolated from cacao rhizosphere, three isolates (CP07, CP24 and CP30) identified as Pseudomonas chlororaphis, showed in vitro antagonistic activity against P. palmivora. Direct antagonism tested in cacao detached leaves revealed that the isolated rhizobacteria were able to reduce symptom severity upon infection with P. palmivora Mab1, with Ps. chlororaphis CP07 standing out as a potential biocontrol agent. Besides, reduced symptom severity on leaves was also observed in planta where cacao root system was pretreated with the isolated rhizobacteria followed by leaf infection with P. palmivora Mab1. The production of lytic enzymes, siderophores, biosurfactants and HCN, as well as the detection of genes encoding antibiotics, the formation of biofilm, and bacterial motility were also assessed for all three rhizobacterial strains. By using a mutant impaired in viscosin production, derived from CP07, it was found that this particular biosurfactant turned out to be crucial for both motility and biofilm formation, but not for the in vitro antagonism against Phytophthora, although it may contribute to the bioprotection of T. cacao. Conclusions: In the rhizosphere of T. cacao, there are rhizobacteria, such as Ps. chlororaphis, able to protect plants against P. palmivora. Significance and Impact of the Study: This study provides a theoretical basis for the potential use of Ps. chlororaphis CP07 as a biocontrol agent for the protection of cacao plants from P. palmivora infection. © 2015 The Society for Applied Microbiology.

Aislamiento de Bacillus solubilizadores de fosfatos asociados al cultivo del arroz. El objetivo de este trabajo fue determinar la capacidad de bacterias del género Bacillus pro-venientes del cultivo del arroz (Oryza sativa L.) en solubilizar fosfatos. Los aislamientos se obtuvieron utilizando el modelo Microcosmos de los cultivares Iacuba 30 y Perla, en el año 2008 en Bauta, La Habana, Cuba. Hubo 58 aislados, tanto rizosféricos como endófitos de la raíz y de la parte aérea, que presentaban características distintivas del género Bacillus, como respuesta positiva a la tinción de Gram, forma bacilar y formación de endospora. Se realizó la detección cualitativa en cuanto a la capacidad de solubilización de fosfatos. Solo 19 aislamientos mostraron solubilización en medio sólido NBRIP y en algunos casos cambiaron la coloración del medio de azul a amarillo, lo que indica la producción de ácidos. Se seleccionaron los positivos para la cuantificación en medio líquido. Las cepas mostraron un comportamiento diferente cuando se midió el fosfato solubilizado a distintos tiempos, variando el máximo de solubilización. Phosphate solubilization by rice associate Bacillus. The objective pursued with this study was to isolate Bacillus bacteria from rice (Oryza sativa L.) and determine its potential for phosphate solubilization. Isolates were obtained using the Microcosm model from Iacuba 30 and Perla cultivar, established by Bauta (2008) in La Habana, Cuba. Fifty eight isolates were obtained from the rice rhizosphere and inside of the roots and leaves with characteristics typical of Bacillus, such as Gram positive, rod cells and endospore formation. The qualitative capacity of these isolates for phosphate solubilization was assayed in solid NBRIP medium; the results revealed that only 19 strains solubilized inorganic phosphate and some of them changed the medium color from blue to yellow, presumably due to acid excretion. Positives were selected for assay in liquid medium, and they showed different responses in terms of time and maximum phosphate solubilization.