Development of new microbial biostimulants based on Plant Growth-Promoting Rhizobacteria (PGPR) for improving yield, quality and abiotic stress tolerance in crops

Research on microbial biostimulants is relatively new in the field of fertilizers, nevertheless the importance of the use of Plant Growth Promoting Rhizobacteria (PGPR) in agriculture is clear to all. Beneficial effects of PGPR application were widely reported not only in terms of crop productivity and health, but also as soil bioremediation tool, and as an adequate response to soil biodiversity loss. Development of increasingly effective microbial biostimulants may limit the use of chemical fertilizers and represent an environmental-friendly alternative to cope with soil degradation and climate change issue. In this context, the use of microbial biostimulants based on PGPR could help optimize human inputs in agricultural ecosystem, fitting with the agroecological principles. The final goal of this PhD project was to develop a new microbial biostimulant based on PGPR. The investigation started from the study of potential microbial components. The three considered Pseudomonas strains, P. fluorescens Pf4, P. putida S1Pf1, and Pseudomonas spp. 5Vm1k have turned out to be promising bioagents to be used for plant inoculation. Based on their characteristics as IAA-producing bacteria, phosphate solubilizers and siderophores-producing bacteria, all the strains showed the potential as PGPR. However, differences in the extent of PGP performances were observed. Indeed, S1Pf1 strain showed the highest IAA and siderophore production. Pf4 displayed the major phosphate solubilization activity and siderophore production comparable to S1Pf1, whereas 5Vm1k presented a lower PGP potentiality compared to the other two strains. Although qualities of Pf4, S1Pf1, 5Vm1k as PGPRs was reported, further research is required to better understand both PGPR potential and the most efficient method of application.