Verticillium wilt on potato stems and leaves

Disease name: Potato verticillium wilt

The scientific name: Verticillium dahlia

The type of disease: Vascular wilting

Fungal family: Plectosphaerellaceae

1- Introduction:

Potatoes are susceptible to various diseases, and one such disease that can greatly affect their health and production is Verticillium wilt. This devastating disease is caused by the soil fungus Verticillium dahlia, which infects the vascular system of the potato plant, disrupting the transport of water and nutrients.

2- Life cycle:

The life cycle of Verticillium Dahlia involves survival as resistant structures in the soil. These structures, known as microsclerotia, can persist for several years in the absence of a suitable host. Upon encountering a susceptible host, the fungus germinates and infects the plant through the roots. The fungus then colonizes the vascular system, causing wilting and other symptoms.

3- Symptoms:

Potato plants infected with Verticillium wilt exhibit a range of symptoms that progress from mild early signs to advanced and distinct signs, providing growers with valuable clues for diagnosing and managing the disease.

– Early symptoms:

In the initial stages of Verticillium wilt, growers may notice subtle changes in the lower leaves of potato plants. The most common early symptoms include gradual yellowing of leaves and the beginning of wilting. Lower leaves, especially those closest to the soil, may show signs of reduced fullness and overall vigor. In addition, infected plants may exhibit faltering growth, with a noticeable decline in overall health.

Advanced symptoms:

As the infection progresses, more severe symptoms appear affecting different parts of the potato plant. Vessel tissue in stems may undergo brown discoloration, indicating fungal colonization of the plant's vessels. Leaves and stems may undergo necrosis, resulting in dark, dead tissue. Premature defoliation, where leaves fall before reaching full maturity, is another advanced symptom. Together, these signs contribute to reducing the plant's ability to photosynthesize and overall vigor.

- Characteristic symptoms:

Characteristic features of Verticillium wilt include specific characteristics that help confirm the presence of the parasite. When cutting the stems, growers may notice discoloration of the vessels, revealing the effect Verticillium dahlia has on the internal structures of the plant. Another unique indicator is the presence of lesions on the surface of the tuber in a “V” shape. These lesions, often found during post-harvest inspection, are a diagnostic feature that distinguishes Verticillium wilt from other potato diseases. Recognizing these characteristic symptoms is vital for timely implementation of preventive measures.

4- Preferred conditions:

• Season preferences: Verticillium wilt is preferred at moderate temperatures, usually between (21-24) °C in many areas, coinciding with late spring and summer.

• Soil Conditions: Well-drained soil with a pH range of 6.0 to 7.0.

• Environment Preferences – Greenhouses vs. Open Fields: Greenhouse environments with high humidity can facilitate the spread of Verticillium dahlia in greenhouses. Also, conditions in open fields are also favorable, especially in areas with suitable temperatures.

5- Causes of the disease:

Several factors contribute to the spread of Verticillium wilt in potato crops.

• Contaminated soil: The presence of Verticillium dahlia in the soil, whether from previous potato crops or other susceptible hosts, can lead to the onset of the disease.

• Long periods between crop rotations: Extended periods between potato crops in the same field increase the risk of persistence of soil parasites such as Verticillium dahlia.

• Infected plant remains: Infected potato plant remains can be a source of the pathogen for the following crops.

6- Losses from disease:

Verticillium wilt infection can lead to significant production losses and negative effects on potato quality.

• Reduced tuber size: Injury hinders water and nutrient transport, negatively affecting tuber development and resulting in smaller potato size.

• Low productivity: wilting and premature defoliation contribute to a reduced ability to photosynthesize, resulting in a decrease in overall production.

7- Control strategy:

certainly! Let's delve deeper into the Verticillium wilt control strategy, dividing it into three main areas: agricultural practices, chemical control, and organic control.

A- Agricultural practices:

Agricultural practices play a vital role in the control of Verticillium wilt, as they aim to create an unfavorable environment for the parasite to survive and spread.

Examples:

• Crop rotation: Rotate potatoes with non-host crops to break the disease cycle. Choose crops that are not susceptible to Verticillium dahlia, which reduces the parasite's reproduction in the soil.

• Diverse crop sequence: Implement a varied crop sequence to avoid continuous planting of one crop, which prevents the buildup of Verticillium dahlia in the soil.

• Cleanliness: Quickly remove and destroy infected plant remains. This reduces the possibility of plant debris being a source of the pathogen in subsequent seasons.

B- Chemical control:

Fungicides can be used as part of an integrative management strategy to mitigate the impact of Verticillium wilt.

Examples:

• Soil fumigation: Chemicals such as chloropicrin or metam sodium can be used as soil fumigants before planting to reduce the buildup of Verticillium dahlia in the soil.

• Foliicides: Some fungicides, such as azoxystrobin, propiconazole, and thiophanate methyl, may be used during the growth period. Consult local agricultural extension offices for specific recommendations based on regional conditions.

C- Anti-organic:

Organic control methods focus on biological agents and agricultural practices that reduce the effects of Verticillium wilt without the use of synthetic chemicals.

Examples:

• Biofumigation: Grow biofumigation crops like mustard or watercress in rotation. These plants release compounds as they decompose that inhibit soil parasites, including Verticillium dahlia.

• Vital enemies: Beneficial organisms such as Trichoderma spp. and Bacillus spp. On the soil. These parasite-fighting organisms compete with the parasite itself for resources and produce compounds that inhibit its growth.

• Compost Amendments: Microbial diversity can be improved by applying well-rotted compost, which may create a less favorable environment for Verticillium dahlia.

Integrated approach:

A comprehensive strategy often includes integrating elements from each category to create a comprehensive management plan tailored to the particular farming conditions.

Example: Integrated Pest Management (IPM): Implementing IPM involves using a combination of cultural practices, chemical treatments when necessary, and biological enemies. Monitoring the system regularly and adjusting the strategy based on plant growth stage and disease pressure contributes to a more effective and sustainable approach.

By incorporating these measures into their potato growing practices, farmers can enhance the resilience of their crops against Verticillium wilt, promoting a healthy and productive harvest.

8- Preventive measures:

Effective prevention is crucial to mitigate the risk of potato crops being infected with Verticillium wilt.

• Soil testing: Regularly check the soil for the presence of Verticillium dahlia and adjust control practices according to the results.

• Crop Rotation: Implement a diverse crop rotation to break the disease cycle and reduce parasite persistence.

• Resistant Rootstocks: Use rootstock modified potato varieties on resistant rootstocks to achieve improved protection.

• Surveillance and early detection: Monitor crops regularly to detect symptoms, and remove and destroy infected plants quickly to reduce the spread of the disease.

• Biointervention: Incorporation of biofumigation crops like mustard can help in reducing the level of parasites in the soil.

By integrating these preventive measures with agronomic and chemical practices, farmers can develop a comprehensive strategy to combat Verticillium wilt, ensuring the health and productivity of their potato crops.

9- Conclusion:

Verticillium wilt, caused by Verticillium dahlia, poses a major threat to potato crops globally. With a comprehensive understanding of its life cycle, symptoms and favorable conditions, farmers can implement targeted measures to protect their crops. Also, individuals in the agricultural sector must continue to share information, enhance cooperation, and empower farmers to combat plant diseases, to ensure a sustainable and productive future for potato farming.

Sources:

1. Agrios, G. N. (2005). Plant Pathology. Elsevier Academic Press.

2. Compendium of Ornamental Foliage Plant Diseases. (1998). APS Press.

3. Verticillium Wilt of Potato – A Comprehensive Guide. (2012). American Phytopathological Society.

4. Verticillium dahliae: A Review of Its Pathogenicity, Resistance Mechanisms, and Control. (2017). Frontiers in Microbiology.

5. Toth, I. K., van der Wolf, J. M., Saddler, G., Lojkowska, E., & Hélias, V. (2011). Chapter Five - Verticillium dahliae: Potato Wilt. Advances in Applied Microbiology, 76, 41-61.

6. Plantix – Verticillium Wilt of Potato

7. Crop Protection Compendium. (2020). CABI.

Photos:-

1. https://ipm.ucanr.edu/pmg/images/v/d-po-vdah-st.001banner.png
2. https://www.omafra.gov.on.ca/IPM/images/potatoes/diseases/verticillium/potato_verticillium_04_zoom.jpg
3. https://spudman.com/wp-content/uploads/2021/02/P4010016-scaled.jpg
4. https://www.potatogrower.com/uploads/Potatoes_VerticilliumWilt_JeffMiller1.jpg
5. https://spudman.com/wp-content/uploads/2021/02/S.-tuberosum-Norkotah-wo-w-Vd-scaled.jpg