Fusarium wilt in tomatoes is one of the most common fungal diseases of tomato that is found in all the tomato growing parts of the world. It is highly dangerous and damages almost all parts of the tomato plants including leaves and stem. The plant experiences early death even before vegetative maturity if susceptible varieties of plants are used and the weather is also favorable for multiplication of the fungus. Fusarium wilt generally attacks younger plants but can also attack the older plants in some cases. Fusarium wilt is also a very alarming problem for banana plants.
Description of the pathogen responsible for the disease.
Scientific name – Fusarium oxysporum
Kingdom – Fungi
It is a fungus belonging to the division of Ascomycetes which is responsible for this deadly
disease. The fungus can come from a variety of sources. It can already be present in the soil or it can arrive with the purchased seeds or seedlings. The spores of this fungus can remain viable in soil or in the seeds for at least one year. The disease can occur at any time of the year, but damp and humid conditions of the rainy season typically accelerate the process of multiplication of the fungus. The disease develops more quickly in soils that have higher nitrogen content and lower potassium content. In addition, plants growing in sandy soils tend to contract this disease more often.
Identification of Fusarium fungus.
Since nearly all the fungus species are microscopic in nature, Fusarium is also not an exception. As a result, we cannot see the fungus and identify normally by means of our naked eyes. Only some large colonies specially cultured in laboratories can be seen by means of our normal vision. However, fusarium wilt can be easily identified by carefully studying the symptoms of the disease, such as –
· Yellowing on one side of the stem of the plant or leaves.
· Yellowing begins with older and bottom leaves which are followed by wilting, browning and defoliation.
· Growth of the plant is absolutely stunned.
· Fruit development is very little or decreases to complete zero.
· When the infected stems are cut at the base, brown and damaged vascular tissues can be observed.
· Infected plants tend to die even before attaining maturity.
Stages of growth susceptible to infection.
The fusarium wilt in tomatoes can appear in all stages of the life cycle namely flowering stage,
fruiting stage, post-harvest stage, pre-emergence stage, seedling stage and vegetative growth stage. However, the most susceptible stage of all is the seedling stage.
Damages caused by Fusarium wilt.
Fusarium wilt in tomatoes is one of the most deadly and fearful diseases that cause irreparable damage for the farmers. When the leaves and stem are affected, the yield becomes highly limited and thus the income generated for the farmers decreases drastically. Also, the spreading capability of this fungus is very high which results in difficulty in controlling the spread of the infection once it is initiated. Affected leaves and stems are also responsible for curbing the fruiting capability of the plants.
Life cycle of the fungus.
Fusarium fungus survives in the soil or remains associated with plant residues and seeds for up to ten years. Warm and humid climate accelerates the rate of growth of the fungus. The fungus enters the plant through their roots and then spreads throughout the plant by means of the vascular bundle.
Prevention & Control.
The disease is deadly, but it can be prevented by means of certain steps such as –
1. Use of resistant varieties or cultivars –
Nowadays with the gradual advancement of science, there are a number of genetically engineered disease-resistant tomato cultivars available in the market. Biotechnology has been able to incorporate disease-resistant genes into some improved and varieties of tomato. However, resistant varieties are also not completely immune to the wilt, moderate levels of resistance are present to prevent leaf infection and stem infection. The varieties are labeled VF and include cultivars such as Spring Giant, Burpee VF, Supersonic, Celebrity, Manalucie, Small Fry, etc.
2. Use of Cultural Practices –
This method includes –
· Immediate removal of infected plants from the field to check the spread of the fungi.
· Over application of nitrogen fertilizers should be strictly avoided since higher levels of nitrogen promote the growth of the fungus.
· Avoiding activity in wet plantings since the movement of wet soil from place to place via shoes or tools will spread the disease.
· Tools, implements and tomato cages should be properly sanitized.
· Soil sterilization or fumigation will result in the immediate elimination of fungus. If the fungus still persists, soil replacement should be considered.
· Mechanical removal of weeds or flaming of weeds should be done since many weeds act as the breeding ground for these pathogens.
3. Organic Strategies
· Switching to organic manures like farmyard manure (FYM), vermicompost and cow dung manure would eventually decrease the need for nitrogen fertilizers.
· Mycostop is a biological fungicide that will safely protect crops against the wilt. It can be applied as a soil spray or drench (1-2 gm/100 sq feet) to seedlings. Sufficient water should be provided along within the root zone.
· Solarization of soil for sterilization purposes.
4. Chemical Control –
According to the present researches, fusarium wilt of tomatoes can be treated by means of six fungicides namely benomyl, carbendazim, prochloraz, fludioxonil, bromuconazole and azoxystrobin. They should be used as per the limits instructed in the product labels.