Tomato Fusarium Wilt | Symptoms, Causes & Control

Tomato fusarium wilt is one of the main diseases of tomatoes. The disease has been particularly serious in recent years, which has seriously affected the quality and quality of tomatoes.

Tomato fusarium wilt is a worldwide soil-borne disease that seriously affects tomato greenhouse and field yields. The disease is mainly caused by Fusarium oxysporum f. sp. lycopersici (Fol) and F. oxysporum f. sp. radicis lycopersic (Forl). Although traditional pesticide control can achieve certain control effects, it is easy to cause the resistance of pathogenic bacteria and damage the ecology, and pose a threat to human health.

Symptoms

Tomato fusarium wilt occurs in the base of the stem, branch, and petiole of the plant. Due to the different invading parts of pathogenic bacteria, plant damage symptoms can be divided into two types: whole plant damage and local damage.

Pathogens infect from rhizomes and stem bases: At the initial stage of onset, brown water-stained sunken spots appear on one side of the stem base, elongated or oblong, with slightly raised edges. The color of the leaves above the diseased spots diminished, and then turned yellow, gradually turned brown, and died.
As the disease worsens, the diseased part expands horizontally and vertically to most of the stems are harmed. The top leaves stopped growing and appeared yellowing, the leaves gradually withered from bottom to top, and the whole plant died finally.

Pathogens infect from the base of the side branches: the side branches and the leaves above them gradually yellow and die. Pathogens invade from the base of the ears, and the ears gradually wither. Cut the diseased part, you can see that the vascular bundles have turned light brown or dark brown. When the temperature is high and humid, a pink layer of mildew develops from the disease, which is the conidia of the pathogen.

How to Spread

Fusarium wilt infection and transmission of tomato Fusarium wilt bacteria is extremely specific and only harms tomatoes. Pathogens live through the winter in the soil and spread with rainwater, irrigation water, and soil. The soil temperature of 28 ℃ is suitable for reproduction, the soil is moist, continuous cropping, root damage during farming and excessive nitrogen fertilizer are all prone to disease.

Pathogens in the form of mycelium and chlamydospores live with the diseased remains on the soil, manure, or attached to the seeds, and the pathogens infiltrate from the roots or wounds.

Causes of Tomato Fusarium Wilt


1. Diseases caused by continuous cropping

Continuous cropping of a single crop will cause long-term reproduction and increase of pathogens in the soil, which will increase the degree of damage, cause frequent problems of continuous cropping, and severely limit the development of vegetable production. According to statistics, if the same type of vegetable is repeatedly planted for more than 3 years, the probability of occurrence of fusarium wilt can be as high as 91.12%.

2. Seed carrying pathogens

If organic fertilizer contains plant disease residues or seeds with bacteria, it will increase the risk of tomato fusarium wilt.  At the same time, before seedling, the high temperature and high humidity of seedling bed without strict disinfection of seedling soil and seeds will promote the growth and reproduction of bacteria, leading to the invasion and propagation of bacteria from the seedling root and spread to vascular bundle, and then cause tomato fusarium wilt.

3. Improper field management

When planting tomatoes, scientific and effective measures are not taken for management, such as poor drainage, insufficient base fertilizer, and frequent watering, etc., which will increase the water content of the soil, cause the root system to continue to be in a soil environment that is not conducive to development, and reduce the disease resistance of tomatoes, Fusarium wilt is prone to occur when pathogens invade. In addition, if the soil is insufficient in trace elements and the tomato planting density is too high, it can also cause fusarium wilt.

4. Soil type

If the tomato plant grows well, its resistance to disease will increase and it will be less susceptible to wilt disease.  If the soil permeability is poor and the topsoil layer is shallow, it will inhibit the development of the tomato root system and cause fusarium wilt.  At the same time, tomato is generally planted in neutral or slightly acidic soil, if the soil pH value is lower than 3.5 or higher than 9.0, wilt is not easy to occur, if the soil pH value is 4.5~6, wilt is relatively serious.  

How to Fight Tomato Fusarium Wilt

Tomato fungal diseases have severely affected the yield and quality of tomatoes, reduced their edible value, and caused huge economic losses. At present, the main focus is on chemical control, but pesticide residues are heavy, pathogen resistance and chemical agents are increasingly stressing the ecological environment, and the soil ecological structure has been severely damaged.

Biological control characterized by safety and efficiency has become an alternative measure favored by the market.

The microorganisms that can be applied to the biological control of Fusarium oxysporum mainly include non-pathogenic Fusarium, antagonistic bacteria, actinomycetes, etc. Among them, antagonistic bacteria, as the dominant bacteria in the soil, have the strongest disease-inhibiting ability and the most common applications. Including Bacillus, Pseudomonas, etc.

Beneficial bacteria screened from plant rhizosphere soil or plant body can better symbiotically with host plants, and directly or indirectly promote plant growth and resist the occurrence of pests and diseases by secreting secondary metabolism and other substances.

In addition, Trichoderma harzianum is a good biocontrol microorganism. According to statistics, it has an antagonistic effect on at least 29 pathogenic fungi belonging to 18 genera. It can effectively inhibit the activities of vegetable gray mold, fusarium wilt, and brown spot through the production of antibiotics, hyperparasitoidism, bacteriolysis, and competition. It is a promising biocontrol strain and has a wide range of application scenarios.

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