Semester of Graduation

Spring 2024

Degree

Master of Science (MS)

Department

Department of Plant Pathology and Crop Physiology

Document Type

Thesis

Abstract

Long-term reliance on agrochemicals, such as fertilizers and pesticides, to improve crop productivity can severely impact soil physicochemical properties and health. This eventually leads us to completely depend on these chemicals to sustain the needs of our crops. To resuscitate the deteriorating state of our arable lands, we need to shift from traditional farming to more sustainable crop management. One of the alternatives that we can use instead of these chemicals is the utilization of microorganisms that can perform a variety of beneficial functions for the growth and development of crops. Recently, seed-treating materials made up of bacterial consortia were formulated in our laboratory. These bioinoculants showed beneficial effects on soybean plant growth and yield. In this study, we aim to develop derivatives of these seed-treating materials with a lesser number of strains for easier large-scale preparation without compromising its functions as plant growth-promoting agents. A total of 50 bacterial mixtures were tested for their effects on the soybean seedling vigor, and five bacterial consortia were chosen for further greenhouse and field trials. Among these consortia, the SS04, SS21, and SS44 showed positive effects on the early growth of soybean seedlings, which is important for rapid crop establishment. Notably, plants treated with SS04 consortia consistently showed better seedling growth and biomass, and resistance to biotic diseases such as Cercospora blight and ‘Septoria-like’ symptoms under natural field conditions, when compared to untreated plants. It is recommended to further test these seed-treating materials to ensure their potential as alternatives to agrochemicals. Lastly, to be able to ensure that these bioinoculants are viable when used as seed-treating materials, a bacterial preservation protocol must be optimized. Here, we employ freeze-drying as our means to preserve these beneficial bacteria. Factors affecting the viability of the bacterial cells during and after the extreme process of lyophilization were determined and optimized. Results showed that the combination of 5% cellobiose, 10% glycine betaine, and the inclusion of crude soybean seed extract as the cryoprotective medium yielded the highest number of viable cells after cryo-desiccation. Also, storing lyophilized cells at a lower temperature (4°C) preserved the bacteria better compared to storing them at room temperature. The newly formulated consortia, together with the optimized bacterial preservation method, can serve as a valuable resource to create alternative means to manage the sustainable cultivation of soybean plants.

Date

4-21-2024

Committee Chair

Dr. Jong Hyun Ham

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