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Bacterial Antagonism and Plant Growth Promoting Traits of Actinobacterial Strains Previously Selected for their Antifungal Properties

Aouar L, Lerat S, Boulahrouf A, Beaulieu C

Abstract


Six rhizospheric actinobacteria previously selected for their antifungal properties (Streptomyces griseus Lac1, Streptomyces rochei Lac3, Streptomyces anulatus Pru14, Streptomyces champavatii Pru16, Nocardiopsis dassonvillei subsp. dassonvillei Vic8 and Nocardiopsis alba Pin10) were tested against plant pathogenic bacteria and for several beneficial traits promoting plant growth. In vitro antagonism assay was determined by the plate diffusion method against phytopathogenic bacteria (Streptomyces scabiei EF-35, Agrobacterium tumefaciens AL3, Erwinia amylovora SL1 and Pectobacterium carotovorum CB2). In planta assays were performed on radish seedlings infected with S. scabies EF-35, using growth pouches. The root length was estimated by analysis of data with the Winrhizo software. The indole-3-acetic acid (auxin) and siderophores were produced in liquid culture, detected by colorimetric assay and quantified by HPLC. Phosphate solubilization was determined on Pikovskaya’s agar. Three of the six actinobacterial strains tested in vitro inhibited at least one (out of four) pathogenic bacterium. Strain Lac1 showed the largest growth inhibition spectrum (against Streptomyces scabiei EF-35, Agrobacterium tumefaciens AL3 and Erwinia amylovora SL1), while no actinobacterial strain showed the ability to inhibit the growth of Pectobacterium carotovorum CB2. During in vivo assays, strain Lac1 was the only bacterium to suppress the negative effects on the plant pathogen. All strains presented one or several characteristics of plant growth-promoting rhizobacteria such as indole-3-acetic acid production, phosphate solubilization and siderophores production. This investigation revealed the potential abilities of the six strains for the biological control of plant pathogens, Lac1 emerged as the most promising biocontrol agent.


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