Date of Award

Spring 5-10-2025

Level of Access Assigned by Author

Open-Access Thesis

Language

English

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Committee Advisor

Jianjun Hao

Second Committee Member

Robert Larkin

Third Committee Member

Ibrahim Kutay Ozturk

Abstract

Potato powdery scab caused by Spongospora subterranea f. sp. subterranean can be a significant soilborne disease on potatoes. It is hard to control due to the lack of effective methods. Biological control utilizes beneficial microorganisms, such as plant growth-promoting rhizobacteria (PGPR), to enhance plant health and suppress diseases through various mechanisms. Bacillus velezensis strain BAC03, a PGPR, has previously shown effectiveness in managing Streptomyces scabies. This study investigates the mode of action of B. velezensis BAC03 in controlling powdery scab of potato, a disease caused by Spongospora subterranea f. sp. subterranea (Sss). Through laboratory, greenhouse, and field experiments, the efficacy of BAC03 in disease control was determined and measurement of enzymatic activities in enhancing plant defense. Results showed that BAC03 at 107 CFU/mL can significantly enhance plant growth. Unexpectedly, potato defense enzymes including chitinase, β-1&3 glucanase, peroxidase, and phenylalanine ammonia lyase did not change significantly when it was treated with BAC03. These findings differ from those in previous studies that measured these enzymes directly from the bacteria, rather than assessing the impact of BAC03 on potato plants, which needs further investigation. Due to unfavorable climate conditions, no disease symptoms were observed in any of the experiments, making it impossible to assess the efficacy of BAC03 in controlling powdery scab. Although Spongospora subterranea f. sp. subterranean was not detected, Bacillus velezensis strain BAC03 did not exhibit direct antagonistic effects against the pathogen. However, BAC03 showed potential in enhancing plant growth and resilience, as indicated by increased biomass and tuber weight, particularly with sequential applications. Notably, the highest concentration (10⁸ CFU) led to wilting and yellowing symptoms, suggesting potential phytotoxicity and underscoring the need for careful optimization of application rates in future studies.

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