Phytomicrobiomes (microbial communities associated with plants) are currently recognized as key players in the processes of adaptation of the hosts to biotic and abiotic stress. Within these communities, plant-growth promoting bacteria (PGPB) actively contribute to plant fitness by facilitating access to nutrients, releasing phyto-hormones, degrading or sequestering toxic pollutants, attenuating stress responses, stimulating immune defences and controlling phytopathogenic agents. Microbiome engineering of crops plants, as the targeted manipulation of their microbiomes, is foreseen as a powerful biotechnological tool for sustainable agriculture, expected to face the effects of climate change (e.g. draught, aridity, soil salinization) in an immediate future. The microbiome of halophytes is a well-studied model of the contribution PGPB to salt tolerance of the host. Halotolerant PGPB isolated from halophytes have been successfully tested for improving the performance of their natural hosts and crop plants.
Olive trees, Olea europaea, are drought-tolerant plants, cultivated in Mediterranean regions for millennia, in strictly rain-fed orchards. However, intensive production in high-density orchards requires artificial irrigation. In arid and semi-arid regions, rainfall is often insufficient to ensure the removal of ions introduced with irrigation water, increasing the risk of soil salinization around the roots. Although O. europaea are also relatively tolerant to salt, soil salinization has negative effects on photosynthesis, growth and productivity. By imposing stress, soil salinity may also increase the susceptibility to DISEASE, namely the devastating Olive Quick Decline Syndrome (OQDS) caused by Xylella fastidiosa.
The general objective of project HALIUS is to demonstrate that rhizosphere engineering of an economically relevant crop (Olea europaea) with halotolerant PGPB, selected from an existing library of isolates, can effectively contribute to enhanced tolerance to abiotic (salinity) and biotic (X. fastidiosa infection) stress.
The objectives will be addressed by a two-stage research plan: a descriptive (phenomenologic) field stage and an experimental (laboratory) stage. The initial field stage, intends to characterize the microbiome (endosphere and rhizosphere) of olive trees and soils in representative producing areas and it will be implemented in collaboration with a private partner (CARB-Casa Agrícola Rui Batel). The experimental stage, will follow a factorial experimental design, to test (i) inoculation with selected PGPB, (ii) increased soil salinity and (iii) exposure to phytopathogenic bacterium X. fastidiosa. Young olive trees will be exposed to the combinations of conditions defined for each factor, and the tasks will be focused on the analysis of particular targets: the microbiomes, plant growth and physiological condition and plant susceptibility to disease.
This project represents an interdisciplinary approach, involving a team of microbiologist, plant physiologists, biochemists and geologists, that will address fundamental (microbial ecology) and applied (rhizosphere engineering) perspectives of plant-bacteria interactions: (a) the understanding of the effect of soil salinization on O. europaea microbiomes (rhizosphere and endosphere); (b) the design of bacterial strains/consortia as inoculants for the mitigation of salinity stress in intensive olive orchards; (c) the development of a biological tool to empower olive trees against X. fastidiosa.
The proposal is grounded on the solid previous experience of the team on plant-microbe interactions, mainly structured around two axes: (a) rhizosphere microbiology of halophytes, envisaging the -potential application of halotolerant PGPB in either saline or traditional agriculture; (b) plant-microbe interactions underlying plant responses to stress and disease. All team members have been involved in joint initiatives and the relation with the private company is framed by collaboration protocol. The Research Units involved (CESAM, QOPNA, GEOBIOTEC at the University of Aveiro and the UVa-INIA at the University of Valladolid) gather the competences, infrastructures and equipment required for the implementation of the activities.
The relevance of the topic derives from the economic importance of O. europaea for Mediterranean regions, from the novelty entailed by microbiome engineering approaches for future agriculture and from the alignment with the Sustainable Development Goals of the United Nations agenda for the decade (e.g OSD2 - Zero Hunger; OSD8 - Economic Growth).
