Auxins production by radical endophytes from Populus and Nothofagus trees

GENTILE, IÑAKI; FONTENLA, SONIA; PASTORINO, MARIO JUAN; SEVERINO, ME; MESTRE, CECILIA

La Falda

Workshop; 2do Taller Latinoamericano sobre Rizobacterias Promotoras del Crecimiento de Plantas; 2014

Latin American PGPR Workshop

Introduction Root endophytes are microorganisms that during whole or part of their life cycle, colonize the plants roots without causing disease symptoms. Some endophyte produces metabolites which promote plant growth (such as phytohormones) or enhance resistance of pathogens. Some of the best studied plant growth promoting rhizobacteria (PGPR) are associated to the N2 fixing bacteria group (diazotrophs) and to the genus Pseudomonas sp. and Bacillus sp. Plant production to remediation, reforestation or forestry industry is growing in Patagonia region. Different trees species belonging to the genus Populus and Nothofagus are produced in nursery because of their economic and ecological importance. The objective of this work is to evaluate the production of auxins-like compounds produced by endophytic bacteria isolated from roots of Populus and Nothofagus species. Materials and methods We collected roots from Populus nigra, P. trichocarpa and Nothofagus oblicua in nursery from EEA INTA Bariloche. The collected roots were surface sterilized for culturing and isolating of endophytic bacteria. Isolation media included one general isolation medium (TSA) and selective media for diazotrophs (low N concentration) and for Pseudomonas group (with cetrimide). The semi-quantitative production of auxine-like compounds was determined using Salkowki method on cultures supernatant. Azospirillum brasiliensis AZ39 was used as positive control and a quantification curve was performed using 3-indole-acetic acid (IAA, Sigma). Results We recovered 41 bacterial isolates, 7 of them were assigned to the Pseudomonas group, 16 to the diazotroph group, 2 isolates were able to growth on both low N medium and cetrimide containing medium, 5 isolates showed similar colony morphology to Bacillus mycoides while the other 11 were assigned to a group named ?Other Bacteria?. All the bacteria in the Pseudomonas group produced auxin-like compounds. The maximum value of auxin-like production was found within the diazotroph group with a value of ~30 µg/mL. None of the Bacillus mycoides-like isolates produced auxins at all. Most of the ?Other Bacteria? produced auxins-like compounds. Conclusion The two tree species studied in this work present endophytic bacteriae in their roots. Some of these bacteria isolates are associated to known PGPR groups such as, Pseudomonas sp., diazotroph and Bacillus sp. Most of these endophytic bacteria produced auxins-like compounds showing their potential as plant growth promoters. The diazotrophic bacteriae with the ability to produce auxins-like compounds would be the initial candidates to take part in future studies for possible application in forestry production. Further studies have to be done in order to identify the bacterial isolates and the chemical structure of auxin-like compounds.