Enhancing Resistance to Early Blight and Septoria Leaf Spot in Tomato Hybrids for Sustainable Production in the Southeast

Commodities

Practices

Foliar fungal diseases, specifically Early Blight (EB) and Septoria Leaf Spot (SLS), are catastrophic constraints to tomato production in the humid Southeastern United States, frequently causing yield losses exceeding 50%. Current management relies heavily on intensive fungicide applications, which increase production costs, increase reliance on chemical inputs, and accelerate the development of pathogen resistance. To provide a sustainable alternative, this project proposes developing and evaluating high-quality tomato cultivars with dual resistance to EB and SLS.

The research strategy integrates marker-assisted selection and phenotypic screening to incorporate SLS resistance into elite F₈ lines that have been previously improved for EB resistance. These dual-resistant breeding lines and hybrids will undergo extensive validation at research stations and commercial farms across North Carolina, South Carolina, and Georgia. Trials will specifically compare performance under standard versus reduced fungicide schedules to quantify the genetic contribution to disease suppression.

To ensure commercial viability, collaborating growers will host on-farm trials to assess yield, disease severity, and labor requirements. In coordination with agricultural economists, we will perform partial budget analyses and input-use assessments to calculate the economic and environmental benefits of these new cultivars. Finally, a multi-state outreach initiative, including field days, workshops, and digital extension materials, will facilitate the rapid dissemination of results. By delivering disease-resistant cultivars coupled with practical management strategies, this project aims to enhance grower profitability, reduce chemical dependency, and improve the long-term productivity of the Southeastern tomato industry.

This project aims to improve the long-term viability of fresh-market tomato farming in the Southeastern U.S. by developing and releasing new tomato varieties. These varieties will be resistant to EB and SLS while maintaining high fruit quality. The effort, which includes plant breeding, multi-environment testing, on-farm research, and extension, aims to achieve key outcomes in North Carolina, South Carolina, and Georgia: reducing fungicide use, increasing farm profitability, and improving the quality of life for growers and farm workers.

Objective 1. Identify and incorporate Septoria leaf spot resistance from various germplasm sources into elite F₈ lines with established early blight resistance.

We will confirm sources of SLS resistance by testing a broad range of germplasm, including heirlooms, public breeding lines, and accessions previously reported to be resistant. To ensure suitability under the high humidity and disease pressure prevalent in North Carolina, South Carolina, and Georgia, we will evaluate these accessions under Southeastern growing conditions. Resistant accessions will then be crossed with advanced F₈ tomato inbred lines that have stable EB resistance and desirable fruit quality traits.

We will develop advanced breeding material with resistance to both EB and SLS. This will be achieved by pyramiding and introgressing disease resistance traits, using a combination of phenotypic screening in both field and controlled environments, along with marker-assisted selection where possible. A critical part of the selection process will be preserving key horticultural traits, such as fruit size, color, firmness, and shelf life, while actively minimizing linkage drag associated with the resistance genes. This material will serve as a foundation for subsequent system-level evaluations and hybrid development.

Objective 2. Develop and evaluate dual-resistant tomato breeding lines and hybrids using phenotypic screening and marker-assisted selection across multiple environments.

Advanced lines and hybrids will be developed from the breeding populations established in Objective 1. These new lines will combine high fruit quality with resistance to EB and SLS. We will test across various environments, particularly at research stations and collaborating farms in North Carolina, South Carolina, and Georgia, to evaluate performance under varied climatic conditions, disease pressure, and management practices.

We will conduct field trials comparing fungicide treatments, including standard grower practices and reduced-input systems. These trials will assess disease severity, yield, fruit quality, and overall performance. To improve selection efficiency and accelerate breeding, we will integrate phenotypic screening with marker-assisted selection (where feasible).

We will place strong emphasis on integrating trials managed by breeders, extension faculty, and farmers. This dual approach, spanning both controlled and commercial environments, will enable us to effectively evaluate the performance of promising lines and hybrids. The goal is to identify dual-resistant lines that are agronomically competitive and well-suited for Southeastern production. This strategy will also yield critical data on their performance across various management conditions.

Objective 3. Conduct on-farm trials with cooperating growers in North Carolina and South Carolina to evaluate dual-resistant hybrids under commercial management.

In partnership with participating growers, on-farm validation trials will evaluate selected dual-resistant hybrids under real-world production conditions. These trials will follow standard grower practices and feature side-by-side comparisons of the dual-resistant hybrids with commonly used commercial cultivars. To ensure regional relevance and capture a broader range of variation, trials will be conducted in Georgia in addition to North Carolina and South Carolina. Participating farmers will play an active role in trial setup, crop management, and evaluation of the experimental materials.

Data collected from the participatory trials will include disease severity, yield, fruit quality, and input use, with specific tracking of fungicide application frequency and labor requirements. We will systematically document grower observations and feedback to evaluate cultivar performance, market acceptability, and suitability for current management practices. These insights will be crucial for understanding how dual-resistant cultivars integrate into commercial production systems and how they affect grower decisions on disease control, labor management, and risk mitigation.

The study will comprehensively assess the economic and labor implications of dual-resistant cultivars. Data collection will focus on on-farm metrics, including fungicide applications, overall input costs, and labor time. An agricultural economist at the University of Georgia will conduct a partial budget analysis comparing dual-resistant hybrids with standard commercial cultivars. Fewer fungicide sprays and reduced chemical use will indicate environmental benefits, while labor data will provide insight into workload and operational efficiency. The ultimate goal of these analyses is to provide a holistic perspective on profitability, long-term viability, and improvements to growers' quality of life.

Objective 4. Deliver extension and outreach activities, including field days, workshops, and bulletins, to facilitate the adoption of sustainable, disease-resistant cultivars.

A robust extension and outreach initiative will be developed and implemented across the Southeastern tomato-growing regions to promote the widespread adoption of dual-resistant cultivars and sustainable disease management practices. This program will use a range of resources, including on-farm demonstrations, field days, grower workshops, traditional extension publications, and digital content such as fact sheets.

Outreach efforts will center on farmer-to-farmer knowledge exchange, carried out in partnership with extension specialists, researchers, and participating farmers. Cooperating growers will host demonstration trials, which will serve as key platforms for stakeholder engagement and presentation of project outcomes.

Our outreach strategy emphasizes early and ongoing engagement to maximize project impact. This ongoing interaction with growers creates a feedback loop, enabling iterative refinement of our recommendations. We will develop educational resources for sustained use, tailoring content to the specific needs of audiences, including commercial producers, extension professionals, and other agricultural stakeholders.

We will measure outreach success by tracking planned and actual adoption of recommended practices, along with participant surveys and knowledge assessments. This comprehensive approach ensures that research findings are effectively translated into practical solutions, ultimately improving the profitability, and quality of life for growers in the region.