Abstract
Burkholderia is a versatile bacterial genus and from a biotechnological point of view it is a source of various secondary metabolites with enormous application potential, especially in agriculture. The aim of this study was to isolate Gram-negative diazotrophic endophytic bacteria from rice roots, to select and study the genetic diversity of strains of the genus Burkholderia, as well as the growth promotion mechanisms and the effect of their inoculation in two rice cultivars. Seventy-eight Gram-negative diazotrophic isolates were obtained from 132 root samples of different rice varieties, of which only 5.13% was positive for recA gene amplification with specific Burkholderia primers. Sequence analysis showed high similarity with B. vietnamiensis. These strains produced auxin in broth supplemented with tryptophan (up to 13.98 µg mL-1), siderophores (up to 139.52%), phosphate solubilization (up to 15.99 mg PO4 mL− 1), so too antibiotic and antagonist capacities against five rice pathogenic fungi. These strains increased the vigour index in two rice cultivars compared to the uninoculated or unfertilised treatment. The accumulation of total biomass was high in one strain, with significant differences observed in the response to inoculation at the cultivar level. The antibiotic and antifungal activities of B. vietnamiensis strains against the two pathogenic fungi Nakataea sigmoidea and Nigrospora oryzae are described for the first time. Due to the taxonomic affinity of our strains within the Burkholderia cepacia complex, their direct use in agriculture is not recommended; however, further research is required to exploit their biotechnological potential for the synthesis of useful metabolites.