Exploring Interactions of Phyllosphere Epiphytes with Plant Pathogenic Bacteria Pseudomonas and Xanthomonas on Tomato

<p>Recent studies have indicated the importance of resident microflora of plants in contributing towards overall plant health. Among difference components of the plant microbiome, <em>Methylobacterium</em> and <em>Sphingomonas</em> have been recognized as common residents of the <em>phyllosphere</em> for many host plants, however their role in disease control needs to be further investigated. The purpose of this study was to conduct experiments investigating the effectiveness of <em>phyllosphere</em> <em>Methylobacterium</em> and <em>Sphingomonas</em> isolated from red clover against common tomato <em>phyllosphere</em> bacterial pathogens, <em>Pseudomonas syringae</em> pv. tomato and <em>Xanthomonas perforans</em>. Additionally, this study uses X. <em>perforans</em> wild-type and X. <em>perforans</em> type VI secretion system (T6SS) mutant strains to observe the role of type VI secretion system in infection with a potential biocontrol agent. To explain interactions among the <em>phyllosphere</em> residents, nutritional similarity, motility and direct inhibition were observed <em>in vitro</em>. Based off the literature, it was hypothesized that<em> Sphingomonas</em> would prove to be a potential biocontrol agent against P. <em>syringae pv</em>. tomato, X. <em>perforans</em> wild-type and T6SS mutant. <em>Methylobacteria</em> would not prove to be a potential biocontrol agent against P. <em>syrinage pv</em>. tomato nor X. <em>perforans</em> wild-type and mutant. Lastly, it was hypothesized that X. <em>perforans</em> wild-type would be more virulent than the X. <em>perforans</em> T6SS when competing with a potential biocontrol agent (red clover commensal).</p> <p><em>In planta</em> experiments under growth chamber conditions indicated no significant change in disease with seeds that were soaked in a mix of red clover commensals when dipped in phyllosphere pathogens P. <em>syringae pv</em>. tomato and X. <em>perforans</em> wild-type and T6SS mutant. P. syringae pv. tomato was unable to infect control tomato plants in trial two under growth chamber conditions, and was not tested further<em> in planta</em>. <em>In vitro</em> testing indicated a red clover phyllosphere commensal, <em>S. taxi</em> 55669, inhibited X. <em>perforans</em> wild-type and mutant colonies on R2a plates. Therefore, <em>S. taxi</em> 55669 was studied for disease protection further in the greenhouse with seedling dip experiments. To assess the effectiveness of <em>S. taxi</em> 55669 <em>in planta</em>, foliar disease percent and bacterial population counts were recorded on bacterial dipped seedlings coinoculated with phyllopshere pathogens <em>X.</em> <em>perforans</em> wild-type and T6SS mutant. It is not recommended that <em>S. taxi</em> 55669 serve as a potential biocontrol for P. <em>syringae pv</em>. tomato 99B799 ba ed off the neutral effect S. taxi 55669 had with <em>in vitro</em> testing. Methylobacteria observed in this study, did not show any benefits against disease against <em>P. syringae</em> pv. tomato and <em>X</em>. <em>perforans</em> wild-type and T6SS mutant. However, the results from this study indicate <em>S. taxi</em> 55669 should be studied further for plant health, and has potential as a biocontrol against <em>X. perforans. X. perforans</em> T6SS mutant was found to be less virulent in the presence of <em>S. taxi</em> 55669, than X. perforans wild-type. Based off the high NOI and decrease in foliar disease, this study shows <em>S. taxi</em> 5669 has potential as a biocontrol for<em> X. perforans</em>. The decrease in motility and bacterial populations of <em>X. perforans</em> T6SS mutant when in the presence of <em>S. taxi</em> 55669 highlights the importance of <em>icmF3</em> in motility and ability to attack resident phyllosphere bacteria. The lack of differentiation between direct inhibition on R2a plates of <em>X. perforans</em> wildtype and T6SS mutant in the presence of <em>S. taxi</em> 55669 indicates a part of the T6SS mutant system may still be functional.</p>

Name thesis:degree_name

Biology

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Biology

Year dc:date.available

2020

Author dc:creator

• Turner, Ashley D

Contributors dc:contributor

• Dr. John Davis
• Dr. Neha Potnis
• Dr. Lauren King

• Plant Pathology
• Plant Microbiology
• Biological Control
• Methylobacterium
• Sphingomonas
• Biology
• Botany
• Plant Sciences

Language dc:language

English

Repository record dc:identifier

https://csuepress.columbusstate.edu/theses_dissertations/395

OAI identifier oai:identifier

oai:csuepress.columbusstate.edu:theses_dissertations-1396