CONICET | Buscador de Institutos y Recursos Humanos

At the field, selected PGPR strains must face the competitive pressure imposed by endophytic bacteria that seeds may harbor, as these communities are expected to quickly proliferate after germination. The purpose of this work was to detect diazotrophic bacteria in the seeds of three malting barley cultivars recommended at Buenos Aires productive area, to identify and compare them by molecular tools and to gain insight of their plant growth promoting ability, as well as of their potential antagonistic effects on Azospirillum brasilense strain Az39 (Az39), a well-known collection strain included in some biofertilizers used in Argentina. Following a defined algorithm, 9 diazotrophic isolates were recovered from surface-sterilized barley seeds: 3 from cultivar (cv.) Scarlett, 2 from cv. Quilmes Carisma and 4 from cv. Josefina INTA. Morphologycal studies and routine biochemical tests guided preliminar identification; 16S rRNA gene sequencing was then performed. Sequences obtained were compared to those deposited in public databases. By these means, 5 isolates were identified as Pseudomonas, 2 as Bacillus and 2 as Azospirillum. Genetic relationships between isolates were further investigated by random amplification of polymorphic DNA (RAPD) using three different primers. Indolacetic acid (IAA) biosynthetic ability was estimated by Salkowski technique; N2 fixation potential was determined as acetylene reduction activity (ARA). An adaptation of the double agar layer plate assay allowed screening potential antagonistic effects of isolates against strain Az39. ARA was negligible for all isolates, but in vitro IAA production levels were comparable to that of Az39, our reference strain. No overt antagonistic effects could be detected, but the Azospirillum strain retrieved from Quilmes Carisma cultivar delayed Az39 growth for 72 h, as compared to the other strains tested.