Potencial biotecnológico da comunidade bacteriana endofítica associada a Paspalum vaginatum Swartz na promoção de crescimento vegetal, biocontrole e solubilização de fósforo de rochas fosfatadas

Abstract

Paspalum species are important constituents of native pastures in tropical and subtropical regions of the Americas. Paspalum vaginatum is a native grass to coastal areas in Brazil and is widely used on golf courses in the United States due to its robustness and tolerance to abiotic stresses such as drought, waterlogging, and salinity. Endophytic bacteria present within plant tissues can stimulate their growth and act in the biological control of phytopathogenic organisms. The present study aimed to evaluate the endophytic microbial diversity isolated from Paspalum vaginatum and determine their ability to promote plant growth, in addition to investigating the biotechnological potential of these microorganisms for in vitro phytopathogenic biological control in the laboratory and for the solubilization of different phosphorus sources in vitro and in plant. The 16S rDNA gene of 70 endophytic bacteria isolated from Paspalum vaginatum was sequenced for taxonomic identification purposes. Tests were performed to evaluate antagonism against Colletotrichum sp. and the solubilization capacity of different phosphorus sources such as Rochas Araxá and Bayovar, calcium phosphate and triple superphosphate in vitro. In addition, greenhouse experiments were conducted to study the growth stimulation of the species Paspalum vaginatum and Paspalum maritimum and a phosphorus solubilizing experiment on Paspalum maritimum. Molecular analysis revealed the presence of 17 bacterial genera, with emphasis on Bacillus (34.3%), followed by Agrobacterium and Micrococcus (10% each). The seven bacterial isolates tested were able to solubilize the four different phosphorus sources, with emphasis on Bac 160, Bac 161 and Bac 179. Regarding the antagonistic activity against Colletotrichum sp., it was identified that 13 isolates demonstrated antagonistic activity to the fungus Colletotrichum sp. and presented inhibition index ranging from 12.9% to 43.1%. In the plant growth promotion experiment on Paspalum vaginatum shoot dry weight, plant height and number of basal tillers, the commercial inoculants BiomaPhos® and Biopasto® presented inferior results when compared to the other available treatments. Furthermore, Biopasto® presented inferior results when compared to the other available treatments in relation to the number of aerial tillers in Paspalum vaginatum. In Paspalum maritimum, two varieties of Pantoea sp. contributed to a significant increase in root dry weight compared to the control group, and Biopasto® presented inferior results when compared to the other available treatments for shoot and root dry weight. The collected data point to the biotechnological potential of the endophytic bacterial strains identified in Paspalum vaginatum, indicating possible promising applications in sustainable agriculture both to stimulate plant growth and in the biological control of phytopathogenic organisms. The in plant phosphorus solubilization experiment using Paspalum maritimum was conducted with the isolates Bac 160, Bac 161, and Bac 179. Bac 161 showed favorable results for its use with insoluble phosphorus sources, such as Bayovar phosphate rock, both for shoot and root dry matter. Meanwhile, Bac 160 showed favorable results for use in combination with a soluble phosphorus source in order to enhance its effect.