This Is AuburnElectronic Theses and Dissertations

Soybean growth response to inoculation with plant growth-promoting rhizobacteria supplemented with orange peel amendment




Pacheco da Silva, Maria Leticia

Type of Degree

Master's Thesis


Crop Soils and Environmental Sciences

Restriction Status


Restriction Type

Auburn University Users

Date Available



In order to meet the projected global food demand from population by 2050, current crop production will need to double. In this context, researchers are studying sustainable strategies to improve nutrient absorption by the plants that enhances crop yield such as the use of biofertilizers in agriculture. Plant growth-promoting rhizobacteria (PGPR) have been developed as biofertilizers to promote plant growth. In legume plants, such as soybean, PGPR are associated with more nodulation and therefore higher N2-fixation rate. To exert plant growth promotion, the PGPR must survive and colonize the plant root surface under soil conditions. To persist in the field soils, the inoculated PGPR must compete for carbon source with native microbiota present in the rhizosphere of that specific soil. Researchers have demonstrated that pectin-rich amendments, for instance orange peel, can be degraded by some Bacillus velezensis PGPR strains and used as a sole carbon source, enhancing the PGPR activity and promoting soybean growth and nodulation. Hence, understanding the physiological response of inoculation with PGPR and orange peel on plants is critical. The overall objective of this thesis was to study the effect of inoculation with PGPR supplemented with orange peel amendment on soybean growth parameters. To accomplish this objective, several greenhouse and field experiments were conducted. A preliminary screening with 20 soybean cultivars in the greenhouse showed that the PGPR plus OP treatment produced a positive increase in all plant growth parameters. Further experiments revealed that the environment, soybean cultivar, inoculation method, or the capacity of the PGPR to use orange peel may be also playing an important role in the plant responsiveness.