Introduction
Plant pathogens and pests cause major annual yield losses in many crops grown in Georgia, making timely and accurate disease diagnosis essential for effective management. The Plant Disease Clinic, operated through the University of Georgia’s Department of Plant Pathology, provides routine diagnostic services to commercial vegetable growers and other clients using traditional methods on samples submitted to the Tifton clinic.
As new and emerging diseases become more difficult to diagnose with conventional tools alone, advanced molecular techniques have become increasingly important for confirming plant health problems with greater accuracy and speed. To meet this need, the Tifton clinic collaborates with the Plant Molecular Diagnostic Lab (MDL) to offer affordable, high-quality molecular testing to stakeholders.
Continued funding from the Georgia Agricultural Commodity Commission for Vegetables has been crucial in supporting these services, enabling the clinic to provide advanced, precise, and timely diagnostic testing for vegetable samples at no cost to Georgia growers on a first-come, first-served basis.
Material and Methods
When diseased vegetable samples arrive at the clinic, they are carefully examined for visible symptoms and any signs of pathogens. Diagnosticians look for spots, discoloration, wilting, or patterns of damage. These clues help narrow down the possible causes. They also use microscopes to look for fungal spores, bacteria, nematodes, or other tiny organisms that cannot be seen with the naked eye.
If needed, plant tissues are placed in a moist chamber or in special laboratory media to encourage any pathogens to grow. These samples are then incubated under ideal conditions so that fungi or other microbes, if present, can develop. The shape of spores (conidia) and the appearance of the growing colonies help confirm which pathogen is involved.
In addition to these traditional methods, rapid serological tests such as ImmunoStrips (Agdia) and ELISA are commonly used to detect plant viruses, bacteria, oomycetes, and fungi that affect vegetables. For more precise identification, molecular tests—including PCR, real-time PCR, and DNA sequencing—are performed in coordination with the Plant Molecular Diagnostic Lab. These advanced techniques confirm the exact species and can also detect features such as fungicide or antimicrobial resistance, allowing for a more accurate and detailed diagnosis.
Results
Diagnostic support was provided at no cost to the grower or submitter of the sample in 2025. Between January and November, the Tifton clinic received approximately 233 vegetable samples, including watermelon, cucumber, tomato, potato, onion, pepper, pumpkin, cabbage, collard, beans, squash, cantaloupe, melon, okra, eggplant, turmeric, beet, carrot, broccoli, turnip, and lettuce. Of these, the lab received the most samples of watermelon, pepper, and tomato. Approximately 16% of samples required advanced diagnostics using current DNA/RNA-based lab assays. Samples with bacterial and viral symptoms often require advanced diagnosis to provide efficient management recommendations and address regulatory concerns.
A fast, accurate diagnosis of a problem not only helps reduce yield loss but also allows for selective treatments that can reduce or eliminate unwarranted extra chemical applications. In many cases, this depends on isolating and identifying a plant pathogen.
In 2025, diagnostic services included isolating fungal and oomycetes (85 samples) and bacterial (49 samples) pathogens on growth media. No pathogen was found in 41 samples, and three samples tested positive for a virus. Among the tests used, microscopy and isolation were the primary methods. However, PCR and DNA sequencing were needed for identification in 37 samples (Table 1).
| Testing method | Number of samplesa |
|---|---|
| Microscopy | 143 |
| ImmunoStrip | 67 |
| Isolation on media | 134 |
| Moist chamber | 11 |
| Sequencing | 37 |
| Bacterial streaming | 15 |
| Visual observation | 4 |
| a Many samples (n = 178) required more than one testing method for final confirmation. | |
Conclusion
The Plant Disease Laboratories in Tifton play a central role in supporting the state’s agricultural industry by providing routine diagnostic services to commercial vegetable growers. Through traditional and molecular methods, diagnosticians evaluate plant samples submitted to the Tifton Clinic and provide science-based recommendations for disease management.
The funds provided by the GACCV were instrumental in enabling 233 advanced, accurate, and timely diagnoses of vegetable samples in support of our vegetable growers. We have expanded our molecular diagnostic capabilities for critical and emerging bacterial, fungal, and viral pathogens, including Phytophthora spp., Fusarium oxysporum, Ralstonia spp., and Stemphylium spp.
Improved monitoring and accurate diagnosis of plant diseases ultimately enhanced management recommendations and helped reduce losses caused by plant pathogens.
