title: Paradox of plant growth promotion potential of rhizobacteria and their actual promotion effect on growth of barley (Hordeum vulgare L.) under salt stress.
abstract: From the rhizosphere of two salt tolerant plant species, Hordeum secalinum and Plantago winteri growing in a naturally salt meadow, 100 strains were isolation on enrichment media for various plant growth-promoting (PGP) functions (ACC deaminase activity, auxin synthesis, calcium phosphate mobilization and nitrogen fixation). Based on the taxonomic affiliation of the isolated bacteria and their enrichment medium 22 isolates were selected to test their growth promotion effect on the crop barley (Hordeum vulgare) under salt stress in pot experiment. In parallel the isolates were characterized in pure culture for their plant growth-promoting activities. Surprisingly the best promotors did not display a promising set of PGP activities. Isolates with multiple PGP-activities in pure culture like Microbacterium natoriense strain E38 and Pseudomonas brassicacearum strain E8 did not promote plant growth. The most effective isolate was strain E108 identified as Curtobacterium flaccumfaciens, which increased barley growth up to 300%. In pure culture strain E108 showed only two out of six plant growth promoting activities and would have been neglected. Our results highlight that screening based on pure culture assays may not be suitable for recognition of best plant growth promotion candidates and could preclude the detection of both new PGPR and new plant promotion mechanisms.
authors.affiliation: Institute of Applied Microbiology, Justus-Liebig-University, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Cardinale
authors.affiliation: Institute of Applied Microbiology, Justus-Liebig-University, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Ratering
authors.affiliation: Institute of Applied Microbiology, Justus-Liebig-University, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Suarez
authors.affiliation: Institute of Applied Microbiology, Justus-Liebig-University, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany.
authors.forename: Ana Maria
authors.initials: AM
authors.lastname: Zapata Montoya
authors.affiliation: Institute of Applied Microbiology, Justus-Liebig-University, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany.
authors.forename: Rita
authors.initials: R
authors.lastname: Geissler-Plaum
authors.affiliation: Institute of Applied Microbiology, Justus-Liebig-University, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany. Electronic address: Sylvia.Schnell@umwelt.uni-giessen.de.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Schnell
mesh_terms: D000192:Actinomycetales / Q000302:isolation & purification / Q000502:physiology*; D018533:Biomass; D001467:Hordeum / Q000737:chemistry / Q000254:growth & development / Q000382:microbiology*; D008835:Micrococcaceae / Q000302:isolation & purification / Q000378:metabolism; D009586:Nitrogen Fixation; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000382:microbiology; D010943:Plantago / Q000737:chemistry / Q000254:growth & development / Q000382:microbiology; D012231:Rhizobium / Q000302:isolation & purification / Q000502:physiology*; D058441:Rhizosphere; D055051:Salt-Tolerant Plants / Q000254:growth & development / Q000382:microbiology*; D012988:Soil Microbiology
keywords: Curtobacterium; PGPR, plant microbe interaction, screening method for PGPR; Salt meadow; Salt stress