Progress report for GNE24-323
Project Information
Pennsylvania cultivates about 4,000 acres of fresh market
tomatoes each year, worth $15-20 million. Bacterial speck
(Pseudomonas syringae pv. tomato) causes large
economic losses to the tomato industry, particularly in seedling
production greenhouses, due to planting dense populations and
overhead watering. Current management relies on using treated
disease-free seeds and disease-free transplants. However, limited
effective pesticides and host resistance options necessitates
exploring alternative disease management strategies such as
biocontrol. Previous research focuses on individual strains of
biocontrol agents, which leads to limited efficacy. To address
this problem, our lab has explored the natural foliar microbiome
as the biocontrol of foliar diseases in tomato. Disease
suppression developed following the serial transfer of foliar
communities between sensitive host plants. Building upon this
work, my project aims to evaluate the efficacy of whole microbial
communities in reducing disease incidence in tomato transplants
and across diverse strains of the pathogen. Microbial communities
will be applied to tomato seedlings, followed by pathogen
inoculation at various timepoints or with different strains in a
controlled growth chamber setting. Results will reveal the
potential of microbial communities in mitigating disease
incidence in transplants and their broad-spectrum effectiveness.
These findings will help develop sustainable disease management
strategies. Results will be disseminated at the Mid-Atlantic
Fruit and Vegetable Convention and the National and Northeastern
Divisional American Phytopathological Society meetings.
Additionally, I will publish the findings as a Penn State
Extension Report and in a peer-reviewed journal for widespread
accessibility.
I aim to reduce incidence of bacterial speck in tomato
transplants in a controlled environment setting. My hypothesis is
that inoculating tomato seedlings with suppressive microbial
communities will help to mitigate bacterial speck incidence, and
the disease suppression will persist over time and across the
diverse strains of pathogen.
The specific objectives of this proposal are:
-
Objective 1: to assess the efficacy of suppressive
microbial communities to mitigate bacterial speck in ‘Mountain
Fresh Plus’ tomato transplants. The suppressive microbial
communities, developed by Ehau-Taumaunu and Hockett (2023) will
be evaluated for disease suppression on tomato transplants
within a growth chamber environment. The bacterial pathogen
will be introduced at 2, 7, and 14 days after microbial
community inoculations. The primary focus of the initial phase
is to quantify and analyze the effectiveness of suppressive
communities in reducing bacterial speck incidence in transplant
tomato seedlings. Furthermore, this study elucidates whether
the disease suppression persists over an extended period, our
ultimate goal. Similar study previously done by Koninkx (2023)
reported reduced incidence of bacterial spot of tomato in
transplant production setting.
Expected outcome: It is expected that application of suppressive
microbial communities will reduce bacterial speck incidence in
the tomato transplants.
-
Objective 2: to evaluate the efficacy of suppressive
microbial communities on multiple strains of Pseudomonas
syringae pv. tomato. The aim is to investigate
whether the suppressive microbial communities developed in the
presence of one specific strain (DC3000) by Ehau-Tamaunu and
Hockett (2023) exhibit consistent effectiveness against diverse
strains of the pathogen prevalent in Northeastern United
States. By introducing different strains subsequent to
community inoculations, we will understand the adaptability and
broad-spectrum efficacy of these suppressive communities. The
strains against which communities will be assessed include
Pto T1, and a New York isolate (Kraus et al. 2017;
Orfei et al. 2023)
Expected outcome: This objective will identify the efficacy of
microbial communities against diverse strains of Pseudomonas
syringae pv. tomato.
The purpose of this project is to pioneer biocontrol methods to reduce the incidence of bacterial speck in tomato transplants, addressing a critical issue in the tomato industry.
In 2020, an estimated 12,619 tons of fresh market tomatoes and 11,312,256 tons of processing tomatoes were harvested from nearly 272,900 acres in the United States, with a total value of ~ $1 billion (AGMRC 2021). Pennsylvania contributes about 4,000 acres of fresh-market tomatoes annually, valued at $15-20 million (Orzolek et al. 2006). Bacterial speck, caused by Pseudomonas syringae van Hall pv. tomato (Pto) (Okabe) Young, Dye, & Wilkie (Miller and Jones 1919) causes economic damage to the tomato industry (Goode and Sasser 1980). Over the past five years, it has been a growing problem (Humphreys 2020) and is one of the rising concerns for Pennsylvania tomato growers (PVMRP Research Reports). The pathogen poses urgent challenges in seedling production greenhouses due to high plant population density and overhead watering favoring pathogen spread and disease development. The bacteria then develop as an epiphytic population and go undetected. Once the infected seedlings are transplanted, bacteria further spreads into fields by rain, overhead irrigation, tools, machinery, and workers. The presence of fruit spots reduces the marketable yield of fresh-market tomatoes and prevents complete peeling of the fruit in processing tomatoes (Miller and Jones 2014).
The best way to prevent the disease is using treated, disease-free seeds and transplants (Kravik 2017; Tentinger 2003) as there are only few commercial varieties available with resistance to the pathogen. Current preventative measures include avoiding overwatering, sanitation practices, and copper based bactericides in combination with mancozeb (a broad spectrum fungicide) (Miller and Jones 1919; Wyenandth et al. 2024). The lack of effective pesticides and host resistance options for controlling foliar bacterial diseases in tomatoes has stimulated efforts aimed at exploring alternative strategies (Louws et al. 2001) including biocontrol. Biological control involves using introduced or resident living organisms, to actively reduce the activities and populations of plant pathogens (Pal and Gardener 2006). Research in biocontrol has primarily centered on individual strains of biological control agents (BCA) (Gutesky et al. 2007; Massart et al. 2015). However, the major limitations of using a single organism as a biocontrol agent includes the risk of pathogen refuge (target population that escapes from or not being susceptible to BCA) and competition with local microbes (Johnson 2010; Trivedi et al. 2020). These shortcomings can be overcome by using multiple species as BCA (Gutesky et al. 2007). Additionally, the introduction of exotic species has the potential to affect non-target species and disrupt the ecosystems (Pal and Gardener 2006). This constraint can be addressed by using the organisms already existing in the ecosystem. Thus, selecting entire microbial communities from the same ecosystem for disease reduction can enhance the overall effectiveness of biocontrol. Ehau-Tamaunu and Hockett (2023) used entire microbial communities from tomato fields, which were then passaged 8-9 times onto tomato plants in a controlled environment along with Pto. These microbial communities exhibited disease suppression after 5-6 passages (Figure 1: supporting documents). This project will focus on using these disease suppressive microbial communities (i.e., microbial communities that help suppress plant disease) to mitigate the incidence of bacterial speck in tomato transplants and to assess their efficacy against diverse strains of Pto.
Reduced bacterial speck incidence in tomato transplants achieved through this biocontrol approach is expected to reduce financial burdens on farmers associated with conventional disease management in the field and increase yields of marketable tomatoes. Furthermore, the research aligns with NESARE’s commitment to sustainable and resilient agriculture. Notably, the current use of copper bactericides poses potential risks including phytotoxicity to plants, the development of copper tolerant and resistant strains, and accumulation in soil (Griffin et al. 2017; Lamichhane et al. 2018). By transitioning to biocontrol methods, we aim to reduce the reliance on copper based bactericides, safeguarding long term soil health and fertility. I will take a holistic approach by methodically testing a biocontrol option for tomato disease. This shift towards biocontrol aligns with the principles of Integrated Disease Management (IDM), enhancing resilience in agriculture. Additionally, this project has the potential to serve as a model to develop biocontrol solutions for other foliar bacterial pathogens of tomato such as bacterial canker, as well as for other vegetable crops. Thus, our project signifies the potential for innovative biological control strategies to advance the goals of sustainable agriculture.Supporting document_Livleen
Research
Objective 1. To assess the efficacy of suppressive microbial communities in mitigating bacterial speck in tomato transplants. (Experiment 1)
Plant growth
‘Mountain Fresh Plus’ tomato seeds will be surface disinfested for 1 min in 70% EtOH, then 20 min in 0.1% tween 20, and 5.25% bleach solution, then rinsed three times with MilliQ water. Seeds will be sown in 72-cell trays with professional mix potting media at rate of 1 seed/cell. The trays will be placed in growth chamber with a long-day cycle (16 h of light and 8 h of dark) and 80% relative humidity.
Microbial Community and pathogen inoculations
Tomato seedlings will be spray inoculated with suppressive microbial communities previously developed by Ehau-Tamaunu and Hockett (2023) 10 days after sowing (approximately 0.5 ml/seedling). Pseudomonas syringae pv. tomato (bacterial speck) will be grown in liquid King’s B (KB) media at 28°C for 24 hours. The cells will be centrifuged at 7,197 x g, washed with 10mM MgCl2 buffer two times, and resuspended in 10mM MgCl2. Bacterial suspensions will be standardized to an optical density of 0.3 (108 CFU/ml) at 600nm using spectrophotometer. Pathogen will be spray inoculated at 2, 7, and 14 days after microbial community inoculation.
Experimental design and data analysis
Each treatment will have four trays along with four control trays (with pathogen only inoculation). Two separate trays will serve as control with no inoculations (Figure 2: Supporting document_Livleen). The trays will be placed in a Randomized Complete Block design (RCBD) in the growth chamber. The experiment will be repeated twice. Disease incidence will be recorded (presence or absence of bacterial speck symptoms on each plant) at five, ten, and fifteen days after the pathogen inoculation. Since the data variable are qualitative in nature, Chi square analysis will be used to analyze the data.
Objective 2. To evaluate the efficacy of suppressive microbial communities on multiple strains of Pseudomonas syringae pv. tomato. (Experiment 2).
Plant growth
‘Mountain Fresh Plus’ tomato seeds will be grown in growth chamber similar to objective 1.
Community and pathogen inoculations
Tomato seedlings will be sprayed inoculated with microbial suppressive communities developed by Ehau-Tamaunu and Hockett (2023) 10 days after sowing (approximately 0.5 ml/seedling). Different strains of Pto including DC 3000, T1, and a New York isolate (provided by Dr. Christine Smart, Cornell University) will be grown in liquid King’s B (KB) media at 28°C for 24 hours. The cells will be centrifuged at 7,197 x g, washed with 10mM MgCl2 buffer two times, and resuspended in 10mM MgCl2. Bacterial suspensions will be standardized to an optical density of 0.3 (108 CFU/ml) at 600nm. Pathogen will be spray inoculated at 2 days after community inoculations.
Experimental design and data analysis
Each treatment will have three trays along with three control trays (with pathogen only inoculation). Two separate trays will serve as control with no inoculations and two separate trays for community only control (Figure 3: Supporting document_Livleen). The trays will be placed in a Randomized Complete Block design (RCBD) in the growth chamber. The experiment will be repeated twice. Disease incidence will be recorded (presence or absence of bacterial speck symptoms on each plant) at five, ten, and fifteen days after the pathogen inoculation. Since the data variable are qualitative in nature, Chi square analysis will be used to analyze the data.
Education & Outreach Activities and Participation Summary
Participation Summary:
The project prioritizes a diverse and inclusive outreach plan to share its findings across a wide range of audiences. Throughout the summer of 2024, active participation in vegetable grower twilight meetings in Pennsylvania, organized by Penn State Extension and the Pennsylvania Vegetable Growers Association, will provide a valuable opportunity to interact with local vegetable growers. This aims to open discussion about the challenges they are currently facing in tomato cultivation.
After the completion of the first objective, I intend to present the outcomes at the 2026 Mid-Atlantic Fruit and Vegetable Convention. This convention, supported by grower associations from PA, MD, VT, and NJ, draws growers from all across the Northeast. The presentation will contribute to educational exchange between growers and researchers, fostering a collaborative understanding of the project’s outcome. Continuing the outreach efforts, results will also be presented at the 2026 American Phytopathological Society (APS) Northeastern Division meeting. This event brings together scientists, extension agents, and industry representatives from the Northeast region, providing a platform to share insights on plant disease research and management applications. After the completion of second objective, findings from both the experiments will be presented at 2027 Mid-Atlantic Fruit and Vegetable Convention and 2027 APS Northeastern Division meeting. The comprehensive project findings will also be presented at the national APS meeting in August 2027, enhancing the project’s national visibility. This larger audience comprises international researchers and agents, offering different perspectives and expertise in biological controls and plant disease management strategies. Throughout these outreach opportunities, I will also acknowledge and educate attendees about ongoing research initiatives supported by programs such as the NE SARE.
The project’s principles and findings will be published as a Penn State Extension Report, serving as an educational tool for researchers, growers, and the general public. Simultaneously, the outcomes will also be submitted for publication in a peer-reviewed journal, such as Phytopathology, ensuring credibility and widespread dissemination within the scientific community.
Successful project outcomes will necessitate further outreach efforts to engage tomato farmers, transplant producers, and processing companies. These discussions will explore the effective integration of this approach into tomato management practices. Collaborative efforts with other researchers and extension specialists will help to identify and implement the best application practices for widespread industry adoption.