Potato early dying (PED) is a serious disease that causes potato plants to wilt and die prematurely, leading to significant losses for farmers. A recent study published in the European Journal of Plant Pathology by researchers Julie Pedersen, Isaac Kvesi Abuley, and Sabine Ravnskov from Aarhus University, Denmark, provides valuable insights into the causes of PED and how soil microbes influence the disease.
In the field investigation, eight potato fields were selected, with four fields following the 2-year rotation system and four being virgin fields. All fields were planted with the same potato variety, “Kuras,” and had a similar sandy-clay soil type.
What Causes Potato Early Dying?
PED is primarily caused by a soilborne fungus called Verticillium dahliae. This fungus infects potato plants through their roots, blocking the flow of water and nutrients, which leads to wilting and early death.However, PED is not caused by V. dahliae alone.
Other microorganisms in the soil, such as Colletotrichum coccodes (a fungus that causes black dot disease), have been suspected to make the disease worse. On the other hand, beneficial microbes like arbuscular mycorrhizal fungi (AMF) can help plants resist infections.
The researchers aimed to answer two main questions: First, how do soil microbial communities, shaped by crop rotation practices, affect the severity of PED? Second, does C. coccodes directly worsen PED when combined with V. dahliae?
To find answers, they conducted field surveys and greenhouse experiments, comparing soils from farms with different potato rotation histories.
The Impact of Crop Rotation on PED
The study was conducted in eight potato fields in Central Jutland, Denmark. Half of the fields followed a 2-year rotation system, meaning potatoes were grown every two years.
The other half were virgin fields, where potatoes had not been grown for over 10 years. Both types of fields had the same soil type and climate conditions, ensuring a fair comparison.In each field, the researchers monitored ten plants per plot for six weeks, recording wilting symptoms weekly.
They also collected soil and plant samples to measure the levels of V. dahliae and analyze the soil microbial communities.The results showed significant differences between the two types of fields.
Plants in the 2-year rotation fields started wilting earlier and had more severe symptoms compared to those in virgin fields. By the final assessment, wilting was 33% worse in rotation fields.
Additionally, the levels of V. dahliae DNA in plants were significantly higher in rotation fields, confirming its role as the primary driver of PED.When it came to soil microbes, virgin fields had twice as much AMF biomass compared to rotation fields.
AMF are beneficial fungi that help plants absorb nutrients and resist diseases.Other microbial groups, such as bacteria and fungi, showed no significant differences between the two field types. This suggests that frequent potato cultivation reduces AMF populations, making plants more vulnerable to V. dahliae.
Testing the Role of Soil Microbes and Pathogens
To further investigate the role of soil microbes and pathogens, the researchers conducted a greenhouse experiment using soil from the two field types. They tested how different soil conditions and pathogen combinations affected PED.
The experiment involved two main soil treatments: untreated soil, which retained its natural microbial communities, and heat-treated soil, where microbes were eliminated by heating the soil at 80°C for 48 hours. Plants were then inoculated with V. dahliae, C. coccodes, both pathogens, or neither.
Plants in untreated soil, where natural microbes were present, wilted 20% slower than those in heat-treated soil. This shows that soil microbes play a crucial role in slowing down PED.
Additionally, plants inoculated with V. dahliae wilted faster than uninoculated plants, confirming its dominance in causing the disease.Interestingly, C. coccodes had no significant effect on wilting, whether applied alone or in combination with V. dahliae.
This finding contradicts previous studies that suggested C. coccodes could worsen PED. The researchers explained that C. coccodes was naturally present in all soils, even in uninoculated plants, which might have masked its effects.
Statistical Analysis and Experimental Rigor
The researchers employed robust statistical methods to ensure that the differences observed were significant and not due to random variation. Data from the field and greenhouse studies were analyzed using linear models and generalized least squares (GLS) models to account for unequal variances.
The significance of the effects was determined using F-tests and likelihood ratio tests, and when differences were found, a Tukey HSD post-hoc analysis was conducted with a significance level set at α = 0.05.
This careful statistical approach lends strong support to the conclusion that intensive potato cropping increases PED severity and that a healthy, diverse soil microbial community can mitigate these effects.
Why Soil Microbes Matter in Fighting PED
One of the most important findings of the study is the protective role of soil microbes, particularly AMF. In virgin fields, where AMF levels were twice as high as in rotation fields, plants showed less wilting and lower levels of V. dahliae.
Virgin fields had twice as much AMF biomass, linking higher AMF levels to lower V. dahliae infection and slower disease progression
The study also found that heat-treated soil, where microbes were removed, led to faster wilting and lower plant biomass.This highlights the importance of maintaining a healthy soil ecosystem to support plant growth and disease resistance.
Practical Recommendations for Farmers
Based on the study’s findings, farmers can take several steps to manage PED effectively. First, extending crop rotations can help reduce the buildup of V. dahliae in the soil.Virgin fields, which had not grown potatoes for over 10 years, showed significantly lower levels of the pathogen and healthier plants.
Second, preserving beneficial soil microbes, especially AMF, is crucial. Avoiding excessive tillage and chemical fumigants can help maintain a diverse and healthy microbial community.Finally, monitoring pathogen levels in soil using tools like real-time PCR can help farmers identify high-risk fields and take preventive measures.
Conclusion:
This study highlights that PED is not just a pathogen problem but also a soil health issue. While V. dahliae is the primary driver of the disease, the soil’s microbial community, particularly AMF, plays a vital role in slowing its progression. By adopting longer crop rotations, preserving beneficial microbes, and monitoring pathogen levels, farmers can reduce the impact of PED and improve potato yields.
The findings also emphasize the need for further research into the interactions between soil microbes and pathogens. Understanding these complex relationships can lead to more sustainable and effective strategies for managing PED, reducing the reliance on chemical treatments, and promoting healthier farming systems.
Power Terms
Potato Early Dying (PED): Potato early dying is a disease that affects potato plants, causing them to wilt and die before the crop is fully developed. It is primarily driven by certain soilborne pathogens and can lead to significant yield loss. This term is important because understanding PED helps farmers and researchers develop strategies to reduce losses, such as altering crop rotation practices or improving soil health. In research, PED is measured by assessing the progression of wilt symptoms over time, which can be quantified using disease scoring systems.
Verticillium dahliae: Verticillium dahliae is a soilborne fungus that causes wilt diseases, including potato early dying. It is classified as a hemibiotrophic pathogen because it starts its life cycle by living on the plant without causing immediate damage and later kills plant tissues. Its role is critical in studies of PED since its infection leads to significant plant stress and yield reduction. Researchers often quantify its DNA using molecular techniques like real-time PCR to understand its spread and concentration in infected plants.
Colletotrichum coccodes: Colletotrichum coccodes is another soilborne fungus known to infect potato plants, sometimes causing diseases such as black dot and anthracnose. Although its role in potato early dying is debated, it is studied for its potential to interact with Verticillium dahliae and possibly exacerbate disease symptoms. Understanding this fungus is important for developing integrated disease management strategies, and its detection is carried out using similar methods as for other fungal pathogens.
Soil Microbial Communities: Soil microbial communities refer to the diverse group of organisms—including bacteria, fungi, protozoa, and actinobacteria—that live in the soil. They play a vital role in nutrient cycling, disease suppression, and overall soil health. In the context of PED, the composition and balance of these communities can influence the severity of the disease, as beneficial microbes may help suppress pathogens. Studies often analyze these communities through techniques such as whole cell fatty acid analysis.
Crop Rotation: Crop rotation is the agricultural practice of growing different types of crops in the same area across seasons. This practice is important because it helps maintain soil fertility, reduces the build-up of pathogens like Verticillium dahliae, and supports a diverse soil microbial community. For example, fields that have had a long break from potato cultivation tend to have healthier soils, lower disease incidence, and higher amounts of beneficial fungi such as arbuscular mycorrhizal fungi.
Arbuscular Mycorrhizal Fungi (AMF): Arbuscular mycorrhizal fungi form symbiotic relationships with plant roots by extending the root system with their hyphae, which improves water and nutrient uptake. They are important in maintaining soil health and can help suppress soilborne pathogens, potentially reducing the severity of PED. In research, the abundance of AMF is often measured by analyzing specific fatty acid markers, and their presence is linked to improved plant growth and resilience under stress.
Real-time PCR: Real-time polymerase chain reaction (PCR) is a laboratory technique used to amplify and simultaneously quantify a targeted DNA molecule. It is critical in plant pathology for detecting and measuring the amount of pathogen DNA in plant tissues. The technique works by using fluorescent markers to track the amplification process, and the cycle threshold (Ct) value can be used to calculate the initial amount of DNA, helping researchers assess the infection level of pathogens such as Verticillium dahliae.
Soil Fatty Acid Analysis (WCFA): Whole cell fatty acid analysis is a method used to estimate the biomass of different microbial groups in the soil by identifying their signature fatty acids. This technique is important because it provides a snapshot of the soil microbial community composition, which can influence plant health and disease suppression. In studies of PED, WCFA helps to compare microbial populations between different field rotation systems and understand how these communities affect pathogen dynamics.
Pot Experiment: A pot experiment is a controlled greenhouse study in which plants are grown in pots under set conditions to examine specific variables. This type of experiment is used to simulate field conditions while controlling factors such as soil microbial composition and pathogen inoculation. It is important in research because it allows scientists to study the direct effects of variables like crop rotation, soil treatment, and inoculation with pathogens on disease progression in a manageable setting.
Wilt Progression: Wilt progression refers to the gradual development of wilting symptoms in plants over time due to factors like pathogen infection or water stress. It is a key measurement in studies of diseases like PED because it indicates how quickly and severely a plant is affected. Researchers often use a scoring system that assesses different parts of the plant to quantify wilt progression, thereby providing insights into the effectiveness of management practices.
Inoculation: Inoculation is the process of introducing a pathogen or a beneficial microorganism to a plant to study its effects or to trigger a desired response. In the context of PED research, inoculation involves applying a controlled amount of pathogen spores to potato plants to simulate natural infection conditions. This controlled exposure helps researchers understand how the disease develops and evaluate potential treatments or resistance in different cultivars.
Pathogen: A pathogen is any organism—such as a bacterium, fungus, or virus—that can cause disease in a host organism. In plant pathology, pathogens like Verticillium dahliae and Colletotrichum coccodes are studied because they infect crops, leading to diseases such as PED. Understanding the biology and behavior of pathogens is crucial for developing effective disease management and prevention strategies in agriculture.
Hemibiotrophic Fungus: A hemibiotrophic fungus is a type of fungus that initially establishes a biotrophic relationship with the host—living off the plant without causing immediate harm—and later becomes necrotrophic, killing host tissue to feed on the dead material. This dual lifestyle is significant in the study of diseases like PED because it explains the delayed onset of symptoms and the complex interaction between the pathogen and the host plant. Verticillium dahliae is an example of a hemibiotrophic fungus.
Fungal Interactions: Fungal interactions refer to the various ways in which fungi interact with each other and with other microorganisms in the environment. In the PED complex, these interactions can include synergistic or antagonistic relationships that affect disease severity. Understanding these interactions is important because they can influence the outcome of an infection, either by enhancing the impact of a pathogen or by suppressing it through competition or antagonism.
Rhizosphere: The rhizosphere is the zone of soil immediately surrounding plant roots, where complex interactions occur between the plant, soil, and microorganisms. This area is crucial for nutrient uptake and plant health, and it plays a key role in disease dynamics such as PED. The composition of the microbial community in the rhizosphere can either support plant growth or facilitate pathogen invasion, making it a central focus in agricultural research.
Disease Assessment Scale: The disease assessment scale is a method used to rate the severity of disease symptoms on a plant. In this study, plants were divided into parts and each part was scored on a scale (for example, 0 to 5) based on symptoms like chlorosis, necrosis, or complete wilting. This scale is important because it provides a standardized way to quantify disease severity, making it easier to compare results across different treatments and experiments.
DNA Extraction: DNA extraction is the process of isolating DNA from plant tissues, pathogens, or soil samples. This procedure is essential in molecular biology because it allows researchers to study the genetic material of pathogens like Verticillium dahliae, leading to better understanding of infection mechanisms and resistance. The extracted DNA is then used in techniques like real-time PCR for quantification and identification.
Gas Chromatography (GC): Gas chromatography is an analytical method used to separate and analyze compounds that can be vaporized without decomposition. In soil analysis, GC is used to identify and quantify fatty acids that serve as biomarkers for different microbial groups. This method is important because it provides precise data on the soil microbial composition, which is vital for understanding the interactions that affect diseases like PED.
Mycelia: Mycelia are the network of thread-like structures (hyphae) that form the body of a fungus. They are essential for the fungus’s nutrient absorption and growth. In the context of plant diseases, the spread of mycelia in soil or plant tissue can indicate the progression of a fungal infection. Recognizing mycelial growth is important in diagnosing diseases and understanding how fungi interact with their hosts.
Conidia: Conidia are asexual spores produced by fungi, serving as a means of reproduction and dispersal. They are significant in plant pathology because they enable fungi like Verticillium dahliae and Colletotrichum coccodes to spread and infect new hosts. The formation and release of conidia are often monitored in studies to evaluate the potential of a fungus to cause widespread disease.
Spore Suspension: A spore suspension is a liquid preparation containing fungal spores, created by scrapping fungal cultures and diluting them in water. This method is used to inoculate plants in controlled experiments, ensuring that each plant receives a known quantity of spores. It is important for standardizing infection in research studies, allowing scientists to compare the effects of different pathogens under similar conditions.
Nutrient Solution: A nutrient solution is a water-based mixture containing essential minerals and nutrients required for plant growth. In controlled experiments, such solutions are applied to ensure that plants have sufficient nutrients, which helps isolate the effects of pathogens and other variables. For example, a carefully prepared nutrient solution can minimize nutrient deficiencies so that the impact of a pathogen on plant growth is more accurately assessed.
Linear Model (lm Function in R): A linear model is a statistical method used to understand the relationship between a dependent variable and one or more independent variables. In this study, the lm function in the R programming language was used to analyze data such as disease severity and plant biomass. This method is important because it helps researchers determine whether observed differences between treatments are statistically significant, providing a mathematical basis for conclusions.
Generalized Least Square Model (GLS): The generalized least square model is an advanced statistical technique that accounts for unequal variances in data. It is used in the analysis of complex experimental data where the assumptions of standard linear models might not hold. In the context of this study, GLS helps analyze data on microbial communities and pathogen DNA, ensuring that the results are reliable even when data variability is high.
Spearman Correlation Analysis: Spearman correlation analysis is a non-parametric test used to measure the strength and direction of association between two ranked variables. This method is important in plant pathology research because it can show, for example, whether an increase in beneficial microbes like AMF is linked to a decrease in pathogen levels such as Verticillium dahliae. The Spearman correlation does not assume a normal distribution, making it a versatile tool for analyzing biological data.
Reference:
Pedersen, J., Abuley, I.K. & Ravnskov, S. Fungal interactions in the potato early dying (PED) complex. Eur J Plant Pathol (2025). https://doi.org/10.1007/s10658-025-03024-1
