Inoculation of rhizospheric microbiome from coastal soil is able to enhance salinity tolerance in plants

In the past decades the importance of plant microbiome interactions has become clear, playing a vital role in plant health, growth promotion and tolerance to both abiotic and biotic stress. Soil salinity is an increasingly prevalent abiotic stress which by 2050 is expected to affect 50% of agricultural lands. In addition, Mediterranean soils are also affected by alkalinity since they are usually calcareous and carbonated soils. The research in this thesis is focused on: (1) indicate how the microbiome of the rhizospheric soil of Brassica fruticulosa, a Mediterranean endemic wild brassica, is able to modulate plant tolerance to salt and salt-alkaline stress; and (2) reveal the role of tolerant PGPBs, selected from the coastal microbiome, on the performance of soybean plants exposed to salinity. To achieve these goals, microbial inocula were extracted from four coastal and three inland soil samples of Catalonia, where natural populations of B. fruticulosa can be found. Coastal microbiomes were used to inoculate salt-sensitive B. fruticulosa plants collected from the inland (non-saline) locations exposed to salinity. The results demonstrated the beneficial relationship that exists between rhizospheric microbiome and salt stress tolerance of Brassica plants, that leads to significant changes in total biomass, pigment, proline, hydrogen peroxide and TBARs content in salt and salt-alkaline stress. The research continued with the isolation of the different bacterial populations present in the coastal-adapted microbiome. Subsequently, these microbes were screened for their plant growth promoting activities through different assays. Four different bacterial strain were selected for their potential in growth improvement of plants, other than Brassica, exposed to salt stress. These bacteria were inoculated separately in soybean (Glycine max L.) commercial plants, a valuable moderate salt-tolerant leguminous. The preliminary results of this experiment showed that a couple of these bacterial candidates might be modulating the oxidative response of soybean plants growing under salt stress, pointing out its potential as a future bioinoculant.