Strawberry Soilborne Fungal Disease Testing Trial Shows Why Symptom-Free Does Not Mean Disease-Free
Strawberry plants are highly vulnerable to soilborne fungal pathogens that live in the soil and infect roots, crowns, or lower stems. These diseases can cause stunted growth, wilting, root rot, and eventually plant death. Once established, they are extremely difficult to manage. This is why accurate laboratory diagnostics and soil testing are critical tools for growers and nurseries.
Most cultivated strawberry varieties are susceptible to at least one major soilborne fungal pathogen, including:
- Verticillium dahliae (Verticillium wilt)
- Fusarium oxysporum f. sp. fragariae (Fusarium wilt)
- Phytophthora cactorum (Phytophthora crown and root rot)
- Macrophomina phaseolina (Charcoal rot)
Figure 1:
- Left: Strawberry plant infected with Fusarium oxysporum f. sp. fragariae with severe wilting, leaf necrosis, and vascular discoloration.
- Right: Fof isolated on semi-selective fungal isolation media.
Why Field Diagnosis Can Be Misleading
At first glance foliar symptoms, vascular or crown tissue discoloration may suggest the presence of fungal soilborne pathogens. However, these signs are not always specific to soilborne diseases. Nutrient deficiencies, drought stress, and mechanical injury can create similar discolorations, leading to potential misdiagnosis. In other words, there are limitations in using symptom-based “field diagnosis method” that can render this practice risky.
Even more concerning is the possibility of no visible symptoms during the early stages of infection. In such cases, growers might assume plants are healthy and delay management actions, resulting in serious and lasting agronomic and economic impacts.
Training Trial at CSP Labs
To highlight the importance of proper lab diagnostics, a small training trial was conducted at CSP Labs. Strawberry plants were artificially inoculated with V. dahliae, F. oxysporum f. sp. fragariae (Fof), P. cactorum, and M. phaseolina. Two weeks after inoculation, plants with varying levels of foliar symptoms were uprooted and crowns were cut lengthwise for internal inspection.
A subset of these plants showed no discoloration in the vascular or crown tissue, yet further testing told another story. Using culture-based fungal isolation and molecular testing (qPCR) the results came back positive for all inoculated plants, even those that appeared symptom-free. Mock-inoculated controls tested negative, confirming the accuracy of the results.
Figure 2:
- Top Left Panel: Plant on the left “mock inoculated” (blue arrow), plant on the right is infected with Fusarium oxysporum f. sp. fragariae (red arrow)
- Top Right Panel: Plant on the left “mock inoculated” (blue arrow) & plant on the right is infected with Phytophthora cactorum (red arrow)
- Bottom Left Panel: Plant on the left “mock inoculated” (blue arrow) & plant on the right is infected with Macrophomina phaseolina (red arrow)
- Bottom Right Panel: Plant on the left “mock inoculated” (blue arrow) & plant on the right is infected with Verticillium dahliae (red arrow)
- qPCR results: Orange arrow points at the curves representing the internal positive control; red arrow points at the tested infected tissue, and blue arrow points at tested tissue collected from mock-inoculated (negative control) plants.
What This Means for Growers
This trial underscores the importance of treating vascular discoloration as just one piece of the diagnostic puzzle. When dealing with bare root or dormant strawberry plants, the absence of foliage makes field-based diagnosis even riskier. Testing a small sample of bare root plants before planting is a smart preventative measure. It protects your investment, safeguards soil health, and maintains the long-term viability of your fields—especially when working with valuable or previously clean land.
Get Ahead of Soilborne Diseases Before They Spread
At CSP Labs, we offer high-throughput testing for fungal, bacterial, and viral pathogens. Our assays are designed to handle high-volume nursery submissions and can process composite samples of up to five plants without compromising sensitivity. This ensures accurate and timely results, giving growers confidence before planting.
Consult our strawberry composite sample submission guidelines here or contact our team to learn more about protecting your strawberry production with reliable diagnostics.
