Siderophore and chitinase producing isolates from the rhizosphere of Nicotiana glauca Graham enhance growth and induce systemic resistance in Solanum lycopersicum L

A screening for Plant Growth Promoting Rhizobacteria (PGPR) was carried out in the rhizosphere of wild populations of Nicotiana glauca Graham in south-eastern Spain. Nine hundred and sixty strains were isolated and grouped in four parataxonomic groups: Gram positive endospore forming bacilli, Gram positive non-endospore forming bacilli, Gram negative bacilli and others. Two groups were selected to continue the study: Gram negative bacilli since it was the most abundant, and Gram positive sporulated bacilli, seeking their sporulating capacity as an advantage for inoculants formulation. The ability of these to release siderophores and chitinases in vitro was evaluated. Ninety six isolates were siderophore producers, and 56 of them were also able to produce chitinases. Fifty percent of these were tested for growth promotion in tomato. The best results were obtained with 5 Gram negative bacilli and one Gram positive sporulated bacilli; 5 strains increased all growth parameters while one of them, N21.4, severely compromised plant growth. The ability of these 6 strains to induce systemic resistance against the leaf pathogen Xanthomonas campestris in tomato was evaluated. Five of them effectively reduced disease symptoms (up to 50%). The six strains were identified by 16s rDNA sequencing resulting in 3 Pseudomonas, 1 Bacillus and 2 Stenotrophomonas; it's striking that 2 Pseudomonas protected up to 50% while the other increased disease incidence. This indicates that systemic induction is strain specific and not necessarily related to production of siderophores and chitinases.