Date of Award


Degree Name

Master of Science


Plant and Soil Science

First Advisor

Walters, S. Alan


Biofertilizer (or microbial soil inoculants) may be used to reduce current fertilizer inputs (organic or conventional methods), while maintaining or improving crop plant growth and yield. Pseudomonas putida is a plant-growth promoting rhizobacterium (PGPR) that solubilizes inorganic phosphorous or mineralizes organic phosphates, produces siderophores (enhancing Fe availability for plants, reducing Fe access to pathogenic fungi), and is known to improve plant growth by assisting with nutrient availability, synthesis of plant hormones (indole acetic acid regulation production and/or degradation, or ethylene regulation through aminocyclopropane carboxylate deaminase activity), and acts as a biological control of several plant pathogens and pests (Rhizoctonia solani, Bemisia tabaci). Recommendations for inoculum population density, application timing, and species of PGPR, vary mainly based on geographic and weather conditions, and their relationship to each horticultural crop, which needs to be better understood. Two studies were conducted in 2014 and 2015 at the Southern Illinois Horticulture Research Center to determine the optimum application timing and dosage of Pseudomonas putida strains 17-29 and G11-32 to improve plant growth and yield on two important horticultural crops: field grown ‘Revolution’ bell peppers and greenhouse grown ‘Rocky Top’ determinate tomatoes. Field pepper results indicated that the inoculum population density increased early-season vigor, plant height and stem caliper (P < 0.05), as well as late-season plant vigor, height (cm), leaf chlorophyll index (SPAD), and stem caliper (mm) (P < 0.05) for inoculum population density. Although early harvests (first two harvests) fruit yield increased with rhizobacteria inoculum population density (P < 0.05) for total fruit weight (2014, 2015) and number (2014), late-season fruit yields (last three harvests) were not affected. Combined fruit yield total weight (all five harvests) also increased (P < 0.05) by inoculum population density in the order: 10^0 < 10^3 < 10^5 < 10^7 < 10^9. It appears that higher early-season and combined harvest yields were higher resulting from increasing inoculum population densities were greater due to increased early season growth from the bacterial treatments during plug growth phase. Tomato results indicated that inoculum population density increased early growth and late growth vigor, height (cm), leaf chlorophyll index (SPAD), leaf number, flower number, fresh leaf weight (g), fresh stem weight, and dry leaf weight (P < 0.05). Tomato growth was effected by inoculum population density treatment however, yields differences were not observed.




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