Fusarium wilt is a fungal disease that causes plants to suddenly wither. In this article from “WORLD OF PLANTS,” we review the symptoms of the disease and how to prevent it.
Fusarium wilt
The disease affects a large group of vegetable plants, causing the destruction of the crop. It is considered an obstacle to sustainable agricultural production. It spreads from the Arctic to the tropical regions. Plants are infected with it at any stage of growth. The incidence of the disease in seedlings is high in cold soils. The fungi enter the plant roots infected with nematodes and appear. Infestation in the field in the form of infected spots.
Pathogen: Fusarium oxysporum
This fungus has specialized forms (forma spesiales), abbreviated as f.sp. It infects a specific type of plant, each of which has several strains that differ in their ferocity and spread, including:
F.o.f.sp.conglutinans, which attacks cabbage
The Fusarium genus is a facultative parasite characterized by plant specialization. It does not have a sexual stage, but it produces three types of asexual spores, micro, macro, and chlamydospora. Chlamydospora spores are resistant to drought and adverse conditions, enabling the fungus to survive for long periods in the soil.
Conidia are not usually transmitted through the air, but they can be transmitted through infected plant debris or irrigation water
The fungus penetrates the roots of the sphenoid and lateral plants of the plant host, where Chlamydospiraes (chlamydospiraes) grow, enters the plant's transport vessels, and moves up the plant through the transport vessels, causing their blockage and producing toxins that cause the vessels to become yellow.
Fusarium prefers high temperatures in the soil and air, 23-30°C, and the disease does not occur in soil at temperatures below 20°C.
The disease can be transmitted through vegetative propagation of plants.
Conditions suitable for the spread of Fusarium wilt
The appropriate temperature for the spread of the disease is 23°C, and at 25-30°C the symptoms are severe
It is most active in the summer, June, July and August.
The disease spreads in acidic soils, but soils with a pH of 8 resist the disease.
The disease prefers high humidity
Fusarium infection is more severe in light, sandy, slightly acidic soils
Extremely high temperatures hinder the infection, causing the plants to become stunted, but they do not wilt at the beginning of the infection. However, plants infected at the beginning of the season may show more severe symptoms later in the season.
The fungus spends its life inside the plant vessels, and in the later stages it begins to appear outside the dead plant debris, producing a mass of white hyphae and macroconidia. They are returned to the soil and remain dormant for the next season and can remain dormant for 15-20 years. It activates quickly in soil with a temperature of 20 or above, so the infestation cannot be noticed until June.
Life cycle of Fusarium wilt
The disease is transmitted through the soil, and the Fusarium fungus tends to have a single life cycle, that is, it is not transmitted from one plant to another. However, the time of infection in the field varies from one plant to another according to the density of the fungal inoculum in the soil and not as a result of the fungus being transmitted from one plant to another. There are studies that say that the fungus can It has a multi-life cycle in tomatoes and is able to spread between plants. The disease can be transmitted through contaminated soil, floods, irrigation water, and agricultural tools.
However, the time of symptoms and the rate of disease development in plants varies greatly in the field, giving the appearance of secondary spread.
As the fungus grows in the plant, it produces large numbers of spores on the stem, roots, and other parts.
Also, many of the causes of Fusarium wilt disease are transmitted through seeds, but direct evidence on how seeds are infected is very limited. It is either caused by infected plants or as a result of accidental contamination of seeds during harvesting or extracting seeds.
Symptoms of Fusarium wilt
This pathogenic fungus shows a distinct mode of infection for each crop it infects. Sometimes, plants may show symptoms of wilting at a young age and the leaves will turn yellow. In fully grown plants, wilting appears on parts of the plant. This symptom is common during the hot hours of the day. The leaves begin to turn yellow. This often occurs on one side of the plant's shoot. Cross-sections of the stem show reddish-brown discoloration of the internal tissues, starting at the base of the plant and moving toward the top.
Organic control
Many biological control methods have been used against the Fusarium fungus in many crops, such as bacteria and non-pathogenic strains of Fusarium oxysporum, which compete with the pathogenic fungus and reduce the incidence of disease in some crops. Trichoderma viridii can be used to treat seeds (10 g/kg seeds). Some soil types are able to naturally inhibit Fusarium activity. Adjusting soil pH between 6.5 to 7 and using nitrates as a source of nitrogen instead of ammonium can reduce the severity of the disease.
Chemical control
Integrated preventive measures must be followed, along with biological control, if available. You can use ground-based fungicides by mixing them with the soil in contaminated areas if none of the other methods work. Soak the soil with copper chloride solution (3 g/liter of water) before sowing Agriculture is also an effective method.
Preventative measurements
- Use resistant varieties if available in your area.
- Plants should be monitored and infected plants removed.
- Paying attention to adjusting the soil pH to between 6.5 to 7 and using nitrates as a source of nitrogen (nitrogen).
- Monitor the fields for signs of disease.
- Remove infected plants manually.
- Maintain agricultural machinery and equipment in a clean condition and avoid causing wounds to plants while working in the field.
- Fertilize balanced, focusing on the suggested amount of potash.
- The soil must be deeply plowed and the crop residues must be safely disposed of by burning after harvest.
- Covering infected soil with black plastic wrap on sunny days for a month can kill the pathogenic fungus.
- Following an agricultural cycle of 5 to 7 years can reduce the number of pathogenic fungi in the soil.
Treatment of Fusarium wilt
1- Adding organic matter to the soil and green fertilization, or using green cover crops such as vetch and clover, and plowing them in the spring reduces the infestation because it improves the soil’s permeability and moisture content.
2- Planting in soil free of disease. A propane burner can be used to kill the pathogen on the surface of the soil only, but it does not kill the pathogens present in the depths.
If the soil is infected with the disease, it is preferable to plant grain crops in it.
3- Agricultural rotation. Planting the crop in the same soil should not be repeated until after 5-7 years and only with non-susceptible plants (cereals and corn). This helps reduce the accumulation of Chlamydospora in the soil. However, successive planting of the same crop causes the accumulation of the pathogen to high levels, and if it is not planted Plants of the same species as a previously cultivated plant, and the pathogen can remain dormant in the soil for more than 15 years without a host.
4- Dispose of infected plant waste and burn it.
5- Planting sterilized seeds or treating them with fungal disinfectants, as the disease is transmitted through seeds contaminated with the fungus, and planting resistant varieties, if any, or less susceptible varieties is the basis for alleviating the severity of the disease, as planting resistant varieties in soil infected with the disease reduces the accumulation and density of spores in the soil, in contrast. Susceptible varieties increase the density of pathogenic inoculum in the soil. However, when suitable weather conditions are available for the disease, the incidence of the disease increases even in resistant varieties.
6- Control nematodes using specialized pesticides such as Nemacor two weeks before planting at a rate of 2 liters per dunum or Raji compound at a rate of 3 liters per dunum or Raji Super. As nematodes cause damage to small roots and weaken them, the sensitivity of plants to infection with the disease increases.
7- This disease usually occurs severely and spreads quickly when plants are exposed to various stresses, such as unbalanced nutrition, wet soil, the plant is exposed to drought, iron deficiency in the plant, exposure to herbicides, nematode infection, or root rot.
8- Getting rid of harmful weeds as they are considered hosts for the disease.
9- Continuous field monitoring to detect the disease in order to uproot the infected plants and burn them immediately.
10- Stop irrigating infected spots in the field.
11- Clean agricultural equipment used, as it helps in the spread of the disease from one field to another.
12- Balanced nutrition for plants
13- Modifying the acidity of the soil and raising its pH to 6.5-7 by using dolomite stone in the amount of 5 tons per dunum. The severity of the disease was shown to decrease with the application of lime at a rate of 5 tons per dunum. The decrease in the severity of the disease is due to the increase in calcium levels in the soil. It plays an important role in resisting The plant is resistant to disease. The use of lime with a pH of 5.5 reduces the spread of the disease by 45%.
14- Using grafted varieties. Using red watermelon grafted on zucchini reduced the infection by 88%. Compared with unvaccinated. The two species, Cucrbita and Lagenaria, have also been successfully used as watermelon seeds
15- Sterilize the soil with bazamide, cover with polyethylene, and leave it for 6-8 weeks.
Solar sterilization of the soil using transparent plastic is also used to raise the temperature of the soil. It has been used effectively all over the world. However, it is a cumbersome, tiring and expensive method. It can only reduce the number and clusters of Fusarium in the soil and delay the emergence of the disease. It is effective in countries with climatic conditions favorable to insolation.
16- Biological control using antibiotics, such as the use of soil fungi that produce antibiotics and also the use of bacteria.
Example Gliocladium, Trichderma and pseudomonas.
Streptomyces وHypovirulent strains of fusarium
These non-pathogenic strains compete with pathogenic strains.
17- Disinfect the seedlings before planting to protect them from the fungi that cause root rot (Fusarium solani and Fusarium culmorum) with a mixture of the following compounds:
200 g Rizolix
200 g Rizolix
200 g topsin
The three compounds are placed in 200 liters of water.
#After planting the pesticides used to prevent fusarium wilt, we mention:
Topsin
Quinozol (beltanol).
Hemexazole.
Carbandazim
Plant roots can be activated after transplanting by watering them with humic acid compounds (potassium humate) to give the plant a strong and dense root system.
18- The fungi that cause fusarium wilt prefer high humidity, so frequent irrigation creates a suitable environment for the activity of this fungus, which is hidden in the soil, so irrigation must be regulated.
19- Uprooting the infected plants along with their soil, burning them, disinfecting the soil in the affected areas with quicklime, then spraying it with water to extinguish it as its temperature rises to 120°C. It leads to killing the nematodes causing the infection or using a nematicide.
20- Cleanliness includes sterilizing agricultural equipment and disinfecting seed planting trays
Using nitrogen fertilizers containing nitrates, such as calcium nitrate, instead of those containing ammonium helps control the disease better.
22- Do not over-irrigate, especially during the months of June and July
Using nitrogen fertilizers containing nitrates, such as calcium nitrate, instead of those containing ammonium helps control the disease better.
23- Using black agricultural mulch reduces the infection as it lowers the soil temperature, reduces the growth of fungi, and prevents the growth of harmful weeds that host the wilt fungus.
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