title: Relationship between in vitro characterization and comparative efficacy of plant growth-promoting rhizobacteria for improving cucumber salt tolerance.
abstract: Phosphate solubilization, 1-aminocyclopropane-1-carboxylic acid (ACC)-deaminase activity and production of siderophores and indole acetic acid (IAA) are well-known traits of plant growth-promoting rhizobacteria (PGPR). Here we investigated the expression of these traits as affected by salinity for three PGPR strains (Pseudomonas fluorescens, Bacillus megaterium and Variovorax paradoxus) at two salinity levels [2 and 5 % NaCl (w/v)]. Among the three strains, growth of B. megaterium was the least affected by high salinity. However, P. fluorescens was the best strain for maintaining ACC-deaminase activity, siderophore and IAA production under stressed conditions. V. paradoxus was the least tolerant to salts and had minimal growth and low PGPR trait expression under salt stress. Results of experiment examining the impact of bacterial inoculation on cucumber growth at three salinity levels [1 (normal), 7 and 10 dS m(-1)] revealed that P. fluorescens also had good rhizosphere competence and was the most effective for alleviating the negative impacts of salinity on cucumber growth. The results suggest that in addition to screening the PGPR regarding their effect on growth under salinity, PGPR trait expression is also an important aspect that may be useful for selecting the most promising PGPR bacterial strains for improving plant tolerance to salinity stress.
authors: University of Agriculture Faisalabad, Sub-Campus Burewala, Vehari, Pakistan. smnadeem@uaf.edu.pk.
authors: Sajid Mahmood
authors: SM
authors: Nadeem
authors: Department of Soil Science, University College of Agriculture and Environmental Sciences, The Islamia University of Bahawalpur, Bahawalpur, Pakistan.
authors: Maqshoof
authors: M
authors: Ahmad
authors: Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, 38040, Pakistan.
authors: Muhammad
authors: M
authors: Naveed
authors: Soil Science Division, Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad, Pakistan.|Department of Environmental Sciences, University of California, Riverside, CA, USA.
authors: Muhammad
authors: M
authors: Imran
authors: Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, 38040, Pakistan.
authors: Zahir Ahmad
authors: ZA
authors: Zahir
authors: Department of Environmental Sciences, University of California, Riverside, CA, USA.
authors: David E
authors: DE
authors: Crowley
mesh_terms: D001410:Bacillus megaterium / Q000502:physiology; D018407:Bacterial Physiological Phenomena; D019755:Carbon-Carbon Lyases; D018553:Cucumis sativus / Q000187:drug effects / Q000254:growth & development / Q000382:microbiology* / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics; D007210:Indoleacetic Acids / Q000378:metabolism; D011551:Pseudomonas fluorescens / Q000502:physiology; D054712:Salinity; D055049:Salt Tolerance / Q000502:physiology*; D017262:Siderophores / Q000235:genetics; D012965:Sodium Chloride / Q000494:pharmacology; D012988:Soil Microbiology
chemical_list: D007210:Indoleacetic Acids; D017262:Siderophores; D012965:Sodium Chloride; C030737:indoleacetic acid; C033634:1-aminocyclopropane-1-carboxylate deaminase; D019755:Carbon-Carbon Lyases
keywords: Characterization; Cucumber; Growth; PGPR; Salinity; Stress