Abstract
Natural control of phytopathogenic microorganisms is assumed as a priority function of the commensal plant microbiota. In this study, the suitability of fluorescent pseudomonads in the phyllosphere of crop plants as natural control agents was evaluated. Under field conditions, ears of winter wheat were found to be colonized with high consistency and at a high density by pseudomonads at the late milk dough stage. Isolates of these bacteria were evaluated for their potential to protect the plants from phytopathogenic Alternaria and Fusarium fungi. More Pseudomonas isolates were antagonistically active against alternaria than against fusaria in the dual culture test. The alternaria responded species-specifically and more sensitively to bacterial antagonism than the strain-specific reacting fusaria. A total of 110 randomly selected Pseudomonas isolates were screened for genes involved in the biosynthesis of the antibiotics 2,4-diacetylphloroglucinol, phenazine-1-carboxylic acid, pyoluteorin, and pyrrolnitrin. The key gene for production of the phloroglucinol was found in none of these isolates. At least one of the genes, encoding the biosynthesis of the other antibiotics was detected in 81% of the isolates tested. However, the antagonistic effect found in the dual culture assay was not necessarily associated with the presence of these antibiotic genes. Wheat grains as natural substrate were inoculated with selected antagonistic Pseudomonas isolates and Alternaria and Fusarium strains, respectively. The fungal growth was only slightly delayed, but the mycotoxin production was significantly reduced in most of these approaches. In conclusion, the distribution of phytopathogenic fungi of the genera Alternaria and Fusarium in the field is unlikely to be inhibited by naturally occurring pseudomonads, also because the bacterial antagonists were not evenly distributed in the field. However, pseudomonads can reduce the production of Alternaria and Fusarium mycotoxins in wheat grains and thus have the potential to improve the crop quality.
Highlights
Bacteria of the genus Pseudomonas are commonly found among the predominant genera in plant microbiomes, both in the rhizosphere (Bakker et al, 2013; Donn et al, 2015) and in the phyllosphere (Vorholt, 2012; Bulgarelli et al, 2013; Rastogi et al, 2013), irrespective of the host plant species
We addressed the question of whether fluorescent pseudomonads in the phyllosphere of wheat have an antagonistic potential against Alternaria and Fusarium fungi and besides that, whether they can affect the production of mycotoxins by these fungi as well
The root-born strain Pseudomonas protegens CHA0T (Ramettea et al, 2011), which is able to produce various antagonistic secondary metabolites (Natsch et al, 1994) was used as a reference strain for the detection of genes encoding the biosynthesis of DAPG and pyrrolnitrin
Summary
Bacteria of the genus Pseudomonas are commonly found among the predominant genera in plant microbiomes, both in the rhizosphere (Bakker et al, 2013; Donn et al, 2015) and in the phyllosphere (Vorholt, 2012; Bulgarelli et al, 2013; Rastogi et al, 2013), irrespective of the host plant species. Plant growth-promoting pseudomonads are directly capable of promoting plant growth through the synthesis of growth-stimulating phytohormones or indirectly through enhanced pathogen protection (Haas and Défago, 2005; Wu et al, 2012; Schlaeppi and Bulgarelli, 2015). These activities are attributable to a group of non-phytopathogenic, non-necrogenic species of pseudomonads secreting a yellow-green fluorescent pigment, the siderophore pyoverdine (Meyer et al, 2002), which supports the iron acquisition of bacterial cells (Loper et al, 2012). Siderophores of this type may function as contingent antibiotics and contribute to disease suppression by depriving pathogens of iron
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
