Southern Bacterial Wilt of Tomato Plant: Identification, Prevention & Control

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This is your one-stop guide for understanding, preventing and taking care of the southern bacterial wilt of the tomato plant.

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What is Tomato Southern Bacterial Wilt Disease?

The southern bacterial wilt of the tomato plant is caused by the bacteria Ralstonia solanacearum. 

Race 1 of R. solanacearum is responsible for this disease. It is a root pathogen and is soil-borne bacteria. It is aerobic [requires oxygen for survival] and obligates bacteria. 

It survives in wet and deep soil layers. It survives for several years up to 30 cm deep in many soils. It mainly affects the tomato plants in tropical and subtropical areas. 

How Does it Enter the Tomato Plants?

The southern bacterial wilt of the tomato plant lives in the soil and enters the plant through natural wounds, injuries, and root tips of the plant. 

These wounds are generally either due to manual penetration of roots in the contaminated soil or root-knot nematodes found in the soil. 

What Parts of Plants does it Impact?

It affects the plant vascular system, colonizes the cortex (sub-epidermal tissue), and infects the xylem [tissue that transfers water and minerals to plants]. Eventually, it leads to a deficiency of nutrients in plants, and the plant dies.

As the bacterium spreads in the xylem, it blocks the plant’s water uptake, which leads to wilting and, eventually, death. After the plant dies, the pathogen remains in the debris and survives in the decaying plant material. 

It affects adult tomato plants and seedlings of the plant. It can produce symptoms on leaves, stems, and rarely on fruits. 

The southern bacterial wilt of the tomato plant is very contagious and damages the entire tomato plant quickly. 

How Southern Bacterial Wilt Harm Tomato Plants?

Ralstonia solanacearum is a soil-borne and water-borne disease.

During planting, the roots of the tomato plant get injured and become the source of bacteria entry.

The injuries can also be due to root-knot nematodes, which are plant parasites and reside in the soil.  These root-knot nematodes act as a source of entry for bacteria. They also carry infected bacteria with them, which later infect healthy tomato plants. 

Bacterial wilt pathogen penetrates the root cortex giving access to the vascular tissue. It infects the xylem and, later, the phloem vessels.

The pathogen releases a large number of extracellular polysaccharides (EPS), which increases the viscosity of the vascular stream, thereby hindering the uptake of water. This leads to wilting of leaves. As the bacterium contaminates the xylem, it blocks the plant’s water and minerals uptake, which leads to wilting and, eventually death.

R. solanacearum can survive for years in infected plant material in soils. The probable sources of primary inoculums for the disease are infected soil, infected seed, and weed hosts. This source acts as inoculum and infects healthy tomato plants.  

The spread of the disease from plant to plant occurs through large numbers of bacteria found in the soil from the roots of infected plants. 

Infected plants show southern bacterial wilt symptoms in the afternoon and recover in the evening. Though, at the later stage of development, wilting persists.

The water splashes, overhead watering, and human transmission [contact of infected hands, shoes, tools] might cause the rapid spread of the bacterium within a garden.

 Conditions that facilitate disease development are high temperature [28-32 degrees Celsius], heavy and wet soils [50-100%], and acidic pH.

Check out this video for Southern Bacterial Wilt-

How to Confirm that Southern Bacterial Wilt is Troubling your Tomato Plants?

The symptom that characterizes southern bacterial wilt in the tomato plant is the ‘Wilting of leaves.’ The wilting could be reversible at the initial stage plants might show wilting in the afternoon [hot temperature] and return to normal in the evening. 

This confuses the gardeners with the dehydration of plants however, at the later stage of development, this wilting of young leaves becomes permanent.

Southern bacterial wilt-infected tomato plant either shows all the symptoms of the disease or is asymptomatic [shows no sign]. 

Southern bacterial wilt spreads in the upward direction. It infects secondary roots, large roots, and then the stems.

Check out this video for diagnosis of Southern Bacterial Wilt through the ooze test-

Ways to Control Southern Bacterial Wilt Disease on Tomato Plant

R. solanacearum is challenging to control because of its capacity to survive on various hosts. There are broadly three types of ways by which you can control the southern bacterial wilt of tomato plants.

1. Biological Control
2. Chemical control
3. Cultural control

Biological Control Methods for Southern Bacterial Wilt –

1. The use of antagonists or plants directly reduces the growth of R. solanacearum.
   • Several rhizobacteria [Pseudomonas fluorescens, Bacillus pumilus].

2. The use of suppressive soils
   • Suppressive soils provide conditions that disable pathogen’s will to infect the plant. 
   • It provides rhizosphere bacteria and soil microorganisms.
   • It acts as first line of defense against soil-borne pathogens.

3. Use of Resistant Cultivars

• Tomato cultivars, such as FL7514 and BHN 466 are associated with a reduced quantity of fruits.

Chemical Control Methods for Southern Bacterial Wilt – 

Here are a few ways to control it using chemical methods –

1. The use of bactericides (copper) and antibiotics (streptomycin, ampicillin, tetracycline, and penicillin) can be effective in the control of the disease. However, they are expensive, cause harm to the environment, and damage the tomato plant’s quality. 

2. Soil fumigation/ soil sterilization shows good efficiency only when it is combined with other control methods. The application of chloropicrin is expensive.

3. Soil solarization / Biofumigation [use of organic residues] is a practical solution because it helps in reducing the severity of the disease.

4. The application of Actigard (Syngenta), a plant resistance inducer, in combination with a resistant variety, showed resistance against the southern bacterial wilt disease of the tomato plant. 

5. Lime and wood ash is used as soil pH remediation agents. They are used to raise the pH level of the soil, which decreases bacterial growth in the soil. 

6. A fertilizer without the use of excessive nitrogen should be applied. The amount of fertilizer used should be according to the specified quantity.

7. Transplant your healthy tomato plants in area of good drainage, high soil Ph, less soil moisture and healthy soil.

Check out this video for controlling southern bacterial wilt –

Cultural Control Method for Southern Bacterial Wilt –

Here are few ways –

• Use of crop rotation method – One should always change the position of the tomato plant every two years. 
• Use a well-drained and well – aerated area for tomato plant cultivation.
• Mulch your tomato plants with lots of organic matter especially, calcium.
• Stake your tomato plants to maintain a fair distance of 1 hand between ground and leaves.
• Build narrow trenches to enhance the water absorption capacity of roots.

Check out this video on improving soil health infected by Southern wilt –

How to Prevent Southern Bacterial Wilt on Tomato Plants

One cannot remove the bacteria once it has begun to show symptoms in the tomato plant. But, there are some effective preventive measures related to soil and plant hygiene that can reduce the risk of disease in future healthy tomato plants. 

1. Infected tomato plants should be worked with disinfected tools and equipment. You can dip scissors, clippers, gloves, shoes, and other tools in a 2:1 bleach solution. 

2. Gently plant your tomato in the soil and avoid any root injury.

3. Remove the infected root, stem, or plant immediately.

4. Burn the infected leaves in a burn pile.

5. Seedlings bought must be planted in the conditions specified on the label of seeds. 

6. Avoid excessive soil moisture and wetting of foliages.

7. Monitor the seeds, soil, roots, and plants very carefully.

8. Control root-knot nematodes using neem and marigold.

Check out this video for treating root-knot nematodes –

9. Do not work with your plants when wet or sprayed with fertilizer or any other chemicals. 

FAQ’s

Summary

I hope with this guide has provided you with insights into identifying and tackle Southern Bacterial Wilt in Tomato plants. if you have any tips which can help and I have missed, please drop a message!

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