Wilt of Tomato and Brinjal: Cause, Symptoms and Control

• Causal organism of the plant disease
• Symptoms of damages
• Control measures

Also read: Early blight of potato cause, symptoms, and control

The bacterial wilt of tomato (उकठा in Hindi), caused by Ralstonia solanacearum, is a major disease of this crop in areas where the bacterium is well established and soil conditions are favorable for it. In Karnataka, Madhya Pradesh, Weet Bengal, and in Marathawada region of Maharastra this disease poses a constant threat to tomato and eggplant cultivation. The loss in yield may vary between 10.8 and 90.6% depending on the stage of plant growth at which infection occurs and on environmental conditions. Maximum loss occurs during the summer season when the crop is infected within 60 days of planting. The bacterium is same as described under bacterial brown rot and wilt of potato. Races 1 and 3 of the bacterium are mainly associated with tomato and eggplant. The race 1 (high temperature race is predominantly present in the areas where the disease is destructive on eggplant.

Also read: Late blight of potato and its management (control)

Symptoms of Tomato Wilt

• As in potato, the characteristic symptoms of the disease are wilting, stunting, yellowing of the foliage and finally collapse of the entire plant.
• Before the plant wilts lower leaves may first show drooping.
• The vascular system turns brown and if a segment of the lower stem is cut and squeezed it yields bacterial ooze. 04. Development of adventitious roots from the stem is considerably enhanced.
• In many cases, when nematode infection is also present, the stem at the base becomes dark brown and constricted, leading to collapse of the plant.
• During a continued wet weather when the temperature is also high the most conspicuous symptom in tomato and eggplant is sudden drooping of the leaves without yellowing, and rotting of the stem from any point.
• The roots appear healthy and are often well developed. However, the brown discoloration is present inside.

Cause of the Wilt of Tomato

The pathogen is soil borne, persisting for long periods in some soils. Intact roots are not invaded. Infection always occurs through wounds caused by transplanting, cultural operations or nematode invasion. Root knot infection predisposes to bacterial infection (Ref 01). Rifts in root cortex and breaking of the stem for emergence of adventitious roots also provide opening for entry of the bacteria.

The role of weeds in the epidemiology of bacterial wilt of tomato: One species of portulaca harbor the bacterium.

Mode of action

The entry of the bacteria in the taproot is faster in susceptible than in resistant cultivars. However, once inside the root the bacteria colonize, to some extent, almost all regions of the susceptible and resistant plants.

The organism first moves in to the large xylem vessels. The bacterial cells and EPS get disturbed throughout the vascular bundles and intercellular spaces of the pith in susceptible cultivars whereas is the resistant cultivars they are restricted to the vascular tissues. The strains of the bacterium lacking EPS do not colonize tomato stems as fast as thr strains producing EPS.

When a single lateral bundle is invaded drooping of leaves is common but if all bundles are invaded the plants wilts. Tendency of excessive adventitious root formation also depends on number of vascular bundle invaded. Adventitious roots develop just outside the invaded bundles.

In a resistant cultivar, the bacteria are observed in the primary xylem tissue but not in the secondary xylem tissue. Necrosis of parenchyma cells is occasional. The pit membranes are often thicker with high electron tendency.

Control of the disease (management of wilt disease of tomato and other solanaceous plants)

Application of superphosphate increases severity of the disease while nitrogen suppresses it. Silicon amendment of soil is known to suppress many fungal diseases of plants by induction of acquired resistance and mechanical tissue barriers. Silicon induces basal resistance in tomato against R. solanacearum by modifying pectic cell wall polysaccharide structure. Increased concentration of Ca in a nutrient solution reduces disease severity in a moderately resistant cultivar.

The organism has a wide range of hosts (all solanaceous vegetables and a number of weeds have been some degree of susceptibility. It is difficult to control the disease by rotation of vegetable crops. Cruciferous vegetables such as cauliflower can be used in the rotation. Changing the fields to cereal cultivation for some years is definitely useful in reducing survival of the pathogen in soil. Soil solarization has been found to significantly suppress bacterial wilt in tomato (Ref 02).

In addition to Bacillus sp. and Pseudomonas fluorescens, Pseudomonas putida has also been used as biocontrol agent against bacterial wilt in tomato.

Pseudomonas putida significantly reduced bacterial wilt incidence when applied to seedling at the time of transplanting.

Among indigenous technologies, use of cow urine, tobacco leaf decoction and mixture of asafetida and turmeric are reported to suppress bacterial wilt in tomato. Cow urine is stored for 2 weeks, diluted with water (1:3) and sprayed on the plants.

References

Ref01: Abawi, G. S. and T. L. Widmer (2000). Impact of soil health management practices om soil borne pathogens, nematodes and root diseases of vegetable crops. Appl. Soil Ecol. 15(1):37

Ref02: Arora, D. K. and A. K. Pandey (1989). Soil solarization for control of soil borne diseases: Theory and application, pp . 429-438. In: V. P. Agnihotri, et. al., (eds). Perspectives in plant pathology. Today and Tomorrow’s Printers and Publishers, New Delhi.

Other references

Jacobsen, B. J. and P. A. Backman (19193). Biological and cultural plant disease controls: Alternatives and supplements to chemicals in IPM stratey. Plant Dis. 77:311

Minuto, A. D. Spadoro et al. (2007). Control of soilborne pathogens of tomato using commercial formulation of streptomyces griseobiride and solarization. Crop protection IN PRESS.