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Sultan Qaboos University (2020)

The Effect of date palm genotype on rhizobacterial community structure under saline environment.

Al-Busaidiyah, Aya Mohamed Salim

Titre : The Effect of date palm genotype on rhizobacterial community structure under saline environment.

Auteur : Al-Busaidiyah, Aya Mohamed Salim.

Université de soutenance : Sultan Qaboos University

Grade : Master of Science (MS) in Biology 2020

Some genotypes of date palm (Phoenix dactylifera L.) are salt-tolerant ; however, other genotypes are significantly affected by salinity. This study aimed to understand the contribution of exophytic plant growth-promoting rhizobacteria (PGPR) in salinity tolerance of two different date palm genotypes. Therefore, rhizospheric bacterial communities of two date palm cultivars of contrasting salinity tolerance were investigated in this study. The salt-tolerant ‘Umsila’ and salt-susceptible ‘Zabad’ plants were exposed to normal and 250 mM NaCl stress conditions. The proximal soils of the roots were collected, DNA was extracted from the soil samples, and a cultureindependent approach using Illumina® MiSeq™ sequence analysis was carried out to identify the bacterial communities present in the soil samples based on the 16S rRNA gene sequences. A culture-dependent approach was carried out in a parallel study to isolate bacterial cells and functionally characterize them. The results revealed 771 operational taxonomic units (OTUs), 62 of which were differentially accumulated in response to salinity than the control samples. Ordination analysis showed significant (P = 0.001) changes among the PGPR communities of date palm in response to salinity in both cultivars compared to the control treatments ; however, the genotype did not show a similar degree of the effect on the microbial communities’ structures. The results also revealed that Proteobacteria was a dominant phylum of a majority of Marinobacter genus. Culture-dependent approaches revealed the isolation of 206 strains, including strains that produced NH3, indole acetic acid (IAA), and 1-aminocyclopropane-1- carboxylic acid (ACC) deaminase and also to solubilize minerals such as Fe3+, PO4 3- , Zn2+ , and K+ . Genotyping of the isolated bacteria showed that the number of strains that contained ACC deaminase (acdS) gene and colonized to the rhizosphere of ‘Zabad’ was higher than the number of strains that harboured that gene and colonized to the rhizosphere of ‘Umsila’ when plants were grown under salinity. This notion may suggest that the PGPR is not the unique source of salinity tolerance for ‘Umsila’. Gnotobiotic root elongation and ACC deaminase enzyme activity assays of two strains isolated in this study (Achromobacter xylosoxidans F2-1-20 and Bacillus pumilus Y24) showed that these strains could significantly enhance the growth of canola seeds under 50 mM NaCl, as indicated by the root growth, apparently by producing ACC deaminase enzyme. The results obtained from this study have offered some insights into the rhizospheric bacterial community distribution among date palm cultivars and showed that the PGPR might contribute to salinity tolerance. However, the plant’s genomic structure is still the primary source of information required for salinity tolerance in date palm.

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