The Effect of Date Palm Genotypes on Rhizobacterial Community Structures under Saline Environments

SIMPLE SUMMARY: Soil salinity is a major global problem and negatively contributes to food production. Some date palm cultivars are tolerant to salinity, but the mechanism behind this tolerance is not yet completely understood. Microbial communities could contribute to salt tolerance traits in plants. However, the degree of contribution toward this trait is unclear in date palms. Therefore, this study aims to verify the influence of microbial communities on salinity tolerance in date palms using culture-free and next-generation DNA sequencing techniques. Upon exposure to saline conditions, changes in the microbial communities of the roots of salt-tolerant (Umsila) and susceptible (Zabad) cultivars were investigated. The results showed that the microbial communities of the cultivars are significantly different when they grow under normal soil conditions. However, when the plants grow under salinity, the microbial communities are similar. This indicates that salinity is a major factor determining the microbial community structure in date palm roots regardless of the plants’ salinity tolerance. Therefore, the date palm’s salinity tolerance is unlikely to be controlled by a special microbial community structure. This information leads scientists to focus on producing new salinity-tolerant date palms using genetics and modern molecular biology techniques rather than applying biofertilizers to existing date palm cultivars. ABSTRACT: Some genotypes of date palms (Phoenix dactylifera L.) are salt-tolerant; however, salinity significantly affects others. This study aimed to determine the root epiphytic bacterial contributions to the salt tolerance mechanism in the date palm and to verify if the salt-tolerant “Umsila” and the salt-susceptible “Zabad” cultivars have different bacterial communities. Therefore, the epiphytic bacterial community structures were investigated in both cultivars when grown under control and salinity conditions. The proximal soils of the roots were collected, the DNA was extracted, and a culture-independent approach using Illumina(®) MiSeq™ sequence analysis was carried out to identify the changes in the bacterial community structures in the soil samples due to the changes in salinity and the genotypes of the plants based on 16S rRNA gene sequencing. While salt tolerance response differences were evident between the two cultivars, the 16S rRNA gene sequencing results revealed 771 operational taxonomic units (OTUs), including 62 that were differentially accumulated in response to salinity. The ordination analysis showed significant (p = 0.001) changes among the communities in response to salinity in both cultivars. However, the results showed that the two cultivars had distinct bacterial communities when grown under controlled conditions, whereas they had a more similar bacterial community structure when grown under salinity conditions. The plant genotype does not affect the epiphyte bacterial community structure under salinity, probably because salinity affects the plant-microbe interaction similarly in both cultivars. Also, the identified rhizospheric bacteria are not directly associated with the root’s physiological processes in response to salinity.