CONICET | Buscador de Institutos y Recursos Humanos

The process of development, production and application of an inoculant for use as biofertilizer, phytostimulant and biocontrol agent is often a complex task with multiple steps that must be optimized. Plant Growth Promoting Bacteria (PGPB) used as inoculants are typically applied to the seed in field crops. After sowing, inoculated bacteria should survive in the rhizosphere, make use of nutrients exuded by the plant root, proliferate and be able to efficiently colonize the entire root system and compete with indigenous microorganisms. After this necessary step some of them are able to enter roots and establish endophytic populations. Inadequate plant growth promotion activity in field experiments has often been correlated to poor root colonization. The study of colonization process will give a more detailed insight into plant?bacterial interactions and lead to a more efficient application of inoculant strains. Several diazotrophic plant-associated Burkholderia species have been described as promising candidates for biotechnological applications. In order to find PGPB for grasses, the aim of this work is to characterize the colonization pattern of Burkholderia tropica MTo-293 when wheat seeds are inoculated under gnotobiotic conditions and, on the other hand, to determine whether this colonization is accompanied by an improvement of yield under field conditions.Wheat seeds were inoculated with B. tropica Mto-293 containing the marker gene gfp and were grown under gnotobiotic conditions. Different inoculant dose and inoculation conditions (with or without protector or antifungal agent) were assayed. Colonization was monitored by plating bacterial suspensions from homogenized tissues (CFU/g fresh weight) and by microscopic localization of bacteria. On the other hand, wild type strain was used to inoculate seeds of wheat for the evaluation of plant growth promotion under field conditions by the measure of grain yield (kg/ha). The experimental design was a randomized complete block design with three replicates and five treatments: 1-non-inoculated control without fertilization, 2-non-inoculated control with phosphate fertilization (+P-N), 3-non-inoculated control with Nitrogen fertilization (-P+N), 4-inoculated +P-N, 5-inoculated -P+N. B. tropica could be isolated from root surfaces (>7.0 log CFU/g fresh weight) and from surface-disinfected and disrupted roots (>5.0 log CFU/g fresh weight). B. tropica was able to colonized wheat tissues at inoculation dose as low as 103 CFU/plant and it was also compatible with the antifungal agent used in these experiments. Microscopic studies showed colonizing bacteria on root hairs, root tips and lateral root emergence sites. In field experiments, inoculated plants showed a consistent increase of grain yields as compared to non-inoculated controls: 4% and 3% over their controls without N and P, respectively.These results show that inoculation of wheat seeds with B. tropica led to an extensive root colonization of wheat plants and this significant colonization was accompanied by an enhancement of wheat grain production. Further studies are required to determine whether this effect is because of biological nitrogen fixation, phosphate solubilization or any other growth promotion mechanism that conduce to enhance wheat grain yield.