Rhizospheric bacteria isolation and characterization from saline areas of Santiago del Estero and their effect on germination and early growth of maize under salt stress conditions

COSTA GUTIERREZ SB; LAMI, MARÍA JESUS; MICHAVILA G; ZENOFF AM; CARAM DI SANTOS, CAROLINA; ADLER CONRADO; MARÍA F. POMARES; PAULA A VINCENT; ESPINOSA-URGEL M; DE CRISTÓBAL RE

La Falda Córdoba

Workshop; pgpr Latinoamérica 2014; 2014

Universidad Nacional de Río Cuarto

Introduction The rhizosphere soil region is in intimate contact with plant roots. The bacteria that inhabit the rhizosphere and have a positive effect on plants are called plant growth promoting rhizobacteria (PGPR). Because of this property, these bacteria have the potential to be used as biofertilizers and biocontrol agents. Also, PGPR can confer resistance to soil salinity by producing extracellular polymers that absorb water and therefore increase the water availability in the colonized roots. In this work we isolated and characterized rhizospheric bacteria from saline soils in Santiago del Estero. Then, we used the isolates as seed bioinoculants in crops of regional interest and exposed the seedlings to high salinity soils which would usually be considered unsuitable for crops. By using this approach, it could be possible to expand the culturable land towards poor soils and therefore prevent the dismantling of the rich soils of the Tucuman piedmont. Materials and methods Bacteria were isolated from the rhizosphere of woody vegetation from the province of Santiago del Estero. A total of 20 strains were isolated and identified by sequencing the DNA16S gene. They were characterized by studying growth promoting indicators such as phosphate solubilization, production of siderophores, total indole production and additionally we tested their tolerance to salinity using solid LB medium supplemented with different concentrations of NaCl (0.8, 0.9, 1.0 and 1.2 M ). For all assays P. putida KT2440 was used as control strain, which is a quintessential PGPR strain. In vitro experiments were performed with maize. Seeds were germinated in Petri dishes with sterile absorbent paper which was moistened with 1.5 M NaCl solution. Petri dishes were placed into an incubator a 30 ˚C for 1 week. For each isolate, 10 seeds were inoculated and a control was performed with sterile distilled water. In in vivo experiments, 10 maize seeds pretreated with the strains isolated were seeded in speedlings trays with sterile substrate. Then, 7 days old seedlings were reinoculated with the corresponding strain. Seedlings were watered daily with 1.2 M NaCl solution or sterile water as a control. After 20 days, we measured the length of leaves and the main root. Additionally we recorded data comprising wet and dry weight of each evaluated plant. Results 16S DNA analysis revealed that from the 20 isolated strains, 70% belonged to the genus Pseudomonas. By means of a salt stress tolerance screening, which involved growing the isolates in either liquid or solid LB supplemented with NaCl 1.2 M, we were able to select 7 promising isolates (all genus Pseudomonas). In addition to salt stress tolerance, these isolates showed higher capacity of phosphate solubilization and Acetic Indole Acid (AIA) production compared with the control strain P. putida KT2440. When these strains were inoculated on corn seeds and then subjected to salt stressing conditions (80 mM NaCl) we observed a higher percentage germination (both in vivo and in vitro) compared with the non-inoculated control. Inoculated seeds gave origin to seedlings with about 50% higher values in length of blade root and stem and dry-wet weight compared to control. Conclusion The selected strains (PGPR) show an interesting ability to grow in high concentrations of NaCl and increase the germination percentage of corn seeds under salt stress. This feature is of interest given the potential use of the selected isolates as bioinoculants designed for the culture of corn and perhaps other crops (i.e. soybean) in saline soils of our province. Areas temáticas propuestas: Aplicaciones agronómicas (5) Taxones PGPR [Bacillales, Azospirillum, Pseudomonas, actinomycetes, y otros] (1).