Development of phyllosphere suppressive communities towards Xanthomonas perforans and their potential applications as a biological control against bacterial spot of tomato
Open Access
- Author:
- Bartolomeo Koninckx, Constanza
- Graduate Program:
- Plant Pathology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 18, 2023
- Committee Members:
- Maria Del Mar Jimenez Gasco, Program Head/Chair
Kevin Loren Hockett, Thesis Advisor/Co-Advisor
Sharifa G Crandall, Committee Member
Beth Krueger Gugino, Thesis Advisor/Co-Advisor
Sara Hermann, Committee Member - Keywords:
- bacterial spot
phyllosphere suppressive communities
biocontrol
copper-resistant
Xanthomonas - Abstract:
- Tomatoes are the second most important vegetable crop in the world. Every year, farmers experience up to 66% yield losses due to bacterial spot worldwide and relying on frequent copper-based bactericide applications has led to the emergence and proliferation of copper-resistant bacteria. Furthermore, there is a large market in Pennsylvania for greenhouse and high tunnel grown tomatoes which are grown in high density, creating ideal conditions for the rapid spread of bacterial spot. Alternative management strategies must be developed to mitigate this plant disease and reduce resistance. The phyllosphere, or aerial part of the plant, is home to a varied community of microorganisms that interact with their host. It has been demonstrated that phyllosphere microorganisms play a defensive role in pathogen invasion, and it is possible to harness that function to create a versatile biocontrol that could be used in multiple types of tomato production systems and could potentially be effective against copper-sensitive and copper-resistant bacteria. Traditional biological controls consist of a single, often non-indigenous species that is introduced to a system where it competes with others in a changing environment. The inability of biocontrol agents to successfully colonize a given plant surface can be a limiting factor that could result in loss of biocontrol efficacy. Furthermore, environmental factors may not be favorable for the survival of that particular biocontrol, prompting the need to reapply the product in order to maintain the required degree of disease control. Re-application might prove expensive and time-consuming. Using whole communities of native microorganisms in an augmentative biocontrol strategy could improve control consistency. With this strategy, it was hypothesized that the phyllosphere community will functionally contain multiple modes of action, which would limit the pathogen’s ability to evade biological control and thus, enhance suppression. In this project, tomato phyllosphere communities were selected for suppression of bacterial spot by host mediated indirect selection, otherwise known as passaging. Passaging consisted of a series of steps that included extracting the phyllosphere community, spray inoculating it in a new phyllosphere where it would interact with the X. perforans target pathogen, selecting communities based on the lowest disease severity on the leaf and repeating the process. After 6-8 passages the communities became suppressive against the pathogen, which was verified by the loss of disease suppression after autoclaving half of the community suspension before spraying. Suppressive phyllosphere communities were tested as a biocontrol in a simulated tomato transplant system and against a copper resistant X. perforans strain. Tomato transplants showed no decrease in disease incidence until the plants developmental stage approached the vegetative developmental stage of plants used for passaging. Compared to pathogen-only and copper treatments, plants treated with suppressive communities displayed a considerable decrease in disease severity. When a copper-resistant Xanthomonas strain caused the disease, plants treated with copper had the highest disease severity, suggesting that the native phyllosphere community composition may have changed, perhaps affecting individuals who directly or indirectly antagonized the pathogen. The results of this study will help provide the foundation for using phyllosphere suppressive communities in plant disease management and give some new information to utilize on bacterial spot management strategies.