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University of Crete (2019)

Study of endophytic bacteria in halophytes from Crete for promotion of Brassica plants in high salinity conditions

Sagia Angeliki Σαγιά, Αγγελική Γ.

Titre : Study of endophytic bacteria in halophytes from Crete for promotion of Brassica plants in high salinity conditions

Μελέτη ενδοφυτικών βακτηρίων από αλόφυτα της Κρήτης για προώθηση της ανάπτυξης φυτών Brassica υπό συνθήκες αλατότητας

Auteur : Sagia Angeliki Σαγιά, Αγγελική Γ.

Etablissement de soutenance : University of Crete

Grade : Master of Science Thesis 2019

Plats interact with a vast variety of microorganisms above and below the ground. This aggregate of microorganisms forms the plant microbiome and along with the plant genome they consist the, so called, hologenome. Plant microbiome has a direct input in the phenotype of the host and can affect its health, physiology and tolerance in the different existing stresses. The bacteria that interact with a plant can be found either outside or inside of plant tissues and have either beneficial, negative or neutral results on the host. The bacteria that are found inside plant tissues, at some point of their life circle, are called endophytes and sometimes can promote plant growth (Plant Growth Promoting Bacteria-PGPB) with direct or/and indirect mechanisms. The direct mechanisms, basically, helps the plant to handle biotic stress such as plant pathogens, while the indirect mechanisms assist the tolerance of abiotic stresses like drought and salinity. In this project we focused on study of endophytic bacteria from halophytes from the island of Crete. Halophytes are plants that can grow healthy in high salinity conditions and due to this harsh environmental condition, their microbiome could have very interesting properties. Firstly, the isolated bacteria were identified based on the gene that encodes for the 16S rRNA. Subsequently, the bacteria were tested for their ability to inhibit the growth of two economically important plant pathogenic bacteria, Ralstonia solanacearum and Clavibacter michiganensis subsp. michiganensis. The plant pathogens were co-cultivated with the isolated bacteria and after the proper incubation, the inhibition zones were measured. Moreover, some of the isolated bacteria were selected to test the ability to promote the growth of the model plant Arabidopsis thaliana under no stress and under salt stress conditions. More specifically, seeds of A. thaliana were grown in soil where the endophytic bacteria were inoculated. After one month of treatment (normal or salt) the leaves of the plants were weighted fresh and dry. The results of the bacteria identification indicate a taxonomical variety in the rhizosphere of the halophytes while lower taxonomical diversity was found in the phyllosphere. The in vitro screening of the endophytes for inhibition of the two plant pathogens showed some importantly big inhibition zones. Additionally, there are strains that showed inhibition of both of the tested plant pathogenic bacteria. The statistical analysis showed that the difference in dry leaves’ weight of inoculated and mock plants, under no abiotic stress conditions, is statistically important. Although, some strains, individually, showed great increase in the leaves’ weight, under both conditions tested. Concluding, the endophytic bacteria from the selected halophytes showed important properties and needs to be studied further.

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