Bacterial wilt, cause, pathogenesis, symptom and management

Bacterial wilt is a plant disease caused by various species of bacteria, notably Ralstonia solanacearum and Erwinia tracheiphila. These pathogens infect the vascular system of plants, leading to wilting and potential plant death.

Wilting refers to the loss of rigidity in non-woody parts of plants due to loss of water in plant cells, leading to drooping or folding of leaves and stems. This occurs when the turgor pressure within plant cells decreases due to water loss, resulting in diminished cell turgidity and overall plant rigidity.

What cause wilting | Bacterial wilt –

As stated above wilting arise due to loss of water, so this condition can result from several factors, including drought, low temperatures that impair vascular function, high soil salinity, waterlogged soil, or infections by bacteria, fungi, or nematodes. Often, wilting arises from a combination of these factors.

Since we are dealing here bacterial wilt here, further content will cover wilt cause by bacteria. so there are different bacterial species that infect in cause wilting in the plant (Table 1). for exmaple – Ralstonia solanacearum.

​​Table 1 – Different bacterial species that causes bacterial wilt.

Bacterial Agent	Host Plants	Symptom
Ralstonia solanacearum(ormerly called Pseudomonas solanacearum)	Affects solanaceous crops such as tomatoes (Solanum lycopersicum), potatoes (Solanum tuberosum), eggplants (Solanum melongena), peppers (Capsicum spp.), tobacco (Nicotiana tabacum), bananas (Musa spp.), and geraniums (Pelargonium spp.).   It attacks almost 450 plant species in 54 different plant families	wilting of terminal leaves, followed by a sudden and permanent wilt. Addi- tional symptoms are vascular browning, water soaking of pith followed by browning and browning of cortex near the soil line
Erwinia tracheiphila	Infects cucurbits including cucumbers (Cucumis sativus), melons (Cucumis melo), squash (Cucurbita spp.), pumpkins (Cucurbita pepo), and gourds (Cucurbitaceae).	asymptomatic
Clavibacter insidiosus	Primarily affects alfalfa (Medicago sativa), with other hosts including species within the Medicago, Lotus, Melilotus, Onobrychis, and Trifolium genera.
Curtobacterium flaccumfaciens pv. flaccumfaciens	Impacts common beans (Phaseolus vulgaris), scarlet runner beans (Phaseolus coccineus),lima beans (Phaseolus lunatus), peas (Pisum sativum), soybeans (Glycine max), azuki beans (Vigna angularis), mung beans (Vigna radiata), hyacinth beans (Lablab purpureus), and cowpeas (Vigna unguiculata).	plugging the vascular tissue in stems, discolouration and defoliation
Xanthomonas campestris pv. musacearum	cause banana bacterial wilt, hot pepper, tobacco, sesame, cabbage, wheat and barley, Datura stramonium (in Ethiopia), banana relatives (Musa zebrina and Musa ornata) and Canna-lily,	dull green colouration of the lamina which assumes a scalded appearance and wilting back on its midrib, premature ripening of thefruit. When fruits are cut, the sections show unique yellowish blotches and dark brown placental scars.
Xanthomonas translucens pv. graminis	bentgrass	etiolation, small to medium-sized patches of weak turf, turf with excessive senescence and death.
Pantoea stewartii	Stewart’s wilt of corn	seedling wilt (when the growing point dies) and leaf blight (white lesions on the leaves of older plants).
Enterobacter mori, Pseudomonas syringae pv. mori, Pseudomonas solanacearumand Erwinia carotovora	wilt of Morus alba (mulberry)	browning of vascular tissues, leaf wilt, defoliation and tree decline

So now we have seen that there are many bacteria that cause wilt disease in different plant. So from here one example of wilt disease caused by Rasaltonia solanacearum is being discussed for simplicity and understanding. the other bacteria also follow more are less similar pattern to cause wilting.

Wilt disease caused by Rasaltonia solanacearum

Bacterial wilt, caused by Ralstonia solanacearum, is a devastating plant disease characterized by wilting, stunting, and death, primarily affecting vascular tissues, especially in solanaceous and cucurbitaceous crops.

The R. solanacearum species is composed of a very large group of strains varying in their geographical origin, host range and pathogenic behaviour and is nowadays recognized as a ‘species complex’ which has been divided into four main phylotypes (phylogenetic grouping of strains)

Host Range of R. solanacearum:

The disease affects more than 200 plant species, including tomato, potato, eggplant, banana, and other solanaceous and cucurbitaceous crops.

R. solanacearum pathogenesis/ Diseasecycle or mechanism: general

1. Ralstonia solanacearum is a soil-borne pathogen that enter in plants by wounds, root tips or cracks at the sites of lateral root surface.
2. The bacteria then move into the vascular bundle, hold on to the vessels of xylem or invede the lumen / parenchymatous cells.
3. Here they colonize and produce several pathogenicity factors, including type III effectors, exopolysaccharide (EPS) and cell wall degrading enzymes such as cellulase and pectic lyase
4. With increase in the bacterial number, pathogenic factors and cell wall degrading enzymes also increases which block the vessels.
5. Thus the transport of water disturbed, preventing water flow to the shoot, then resulting in shoot wilting and eventually lead plant death.
6. Recent studies have shown that pathogen survives a symptomless infection in the alternate weed hosts or in presumed non-host plants.

Figure – Pathogenesis steps of bacterial wilting by R. solanacearum. Source : https://eorganic.org/node/34193

Symptoms of bacterial wilt :

• Wilting: Leaves and shoots wilt, especially during the hottest part of the day, and may appear to recover at night. The youngest leaves are usually the first to be affected.
• Stunting: Plants may exhibit stunted growth.
• Discoloration: Vascular tissue (stems) may show discoloration, ranging from light tan to dark brown or black.
• Leaf Spots: In some cases, leaf spots or streaks may also develop.
• Plant Death: In severe cases, the entire plant can wilt and die.
• Bacterial Ooze: When infected stems are cut and squeezed, a bacterial ooze (milky sap) may be evident(bacterial streaming).

Identification of Bacteria R. solanacearum

A selective medium (SMSA) modified by Elphinstone et al. is generally used to distinguish R. solanacearum from other bacteria based on the pink coloured colonies of the former. This medium is used to identify virulent and avirulent strains based on colony morphology. While virulent colonies are fluidal, irregular, white with pink centre, the avirulent colonies are less fluidal, round and red in colour.

Kelman’s triphenyltetrazolium chloride (TZC) agar medium – (Peptone, 10 g; glucose, 2.5 g; Casamino acid, 1 g; agar, 18 g; TZC, 50 mg L-1, can also be used for cultivation of bacteria R. solanacearum; pH 7.0-7.1).

ELISA and polymerase chain reaction (PCR), based on 16S rRNA gene have been successfully used to identification

Figure : Showing health and wilting condition (a), the process sample, inoculum preparation steps (b,c) and the colony characteristics of isolated bacteria(d). Source: Sagar et al., 2014

Control of wilt diesease:

• Prevention:
  • Monitoring: Check for the wilting of plant in crops in day but not recovering, removing them from field to stop the spread.
  • Use disease-free planting material: Choose seeds or seedlings from reputable sources.
  • Soil Management: Improve soil drainage and aeration to reduce stress on plants.
  • Crop Rotation: Rotate crops with non-host plants to reduce the buildup of the pathogen in the soil.
  • Sanitation: Remove infected plant debris to prevent the spread of the disease.
  • Weed Control: Control weeds, as they can serve as alternative hosts for the pathogen.
• Treatment:
  • Resistant Varieties: Use cultivars that are resistant to Ralstonia solanacearum.
  • Biological Control: Consider using beneficial bacteria or fungi to suppress the pathogen.
  • Copper-Based Fungicides: In some cases, copper-based fungicides may be used to control the disease.
• Note: Bacterial wilt can be a persistent problem, and effective control often requires a combination of preventative and treatment strategies.

Source: Raghavendra Reddy Manda, Venkata Avinash Addanki and SewetaSrivastava, 2020

References:

1. Sarkar, S., & Chaudhuri, S. (2016). Bacterial wilt and its management. Current Science, 110(8), 25 April.
2. Sagar, V., Gurjar, M. S., Arjunan, J., Bakade, R. R., Chakrabarti, S. K., Arora, R. K., & Sharma, S. (2014). Phylotype analysis of Ralstonia solanacearum strains causing potato bacterial wilt in Karnataka, India. African Journal of Microbiological Research, 8(12), 1277–1281. https://doi.org/10.5897/AJMR2014.6613
3. Manda, R. R., Addanki, V. A., & Srivastava, S. (2020). Bacterial wilt of solanaceous crops. International Journal of Chemical Studies, 8(6), 1048–1057.
4. Kim, B.-S., French, E., Caldwell, D., Harrington, E. J., & Iyer-Pascuzzi, A. S. (2016). Bacterial wilt disease: Host resistance and pathogen virulence mechanisms. Physiological and Molecular Plant Pathology, 95, 37–43.
5. University of Minnesota Extension. (n.d.). Bacterial wilt. University of Minnesota. Retrieved April 10, 2025, from https://extension.umn.edu/disease-management/bacterial-wilt#using-pes
6. Agriculture Victoria. (n.d.). Bacterial wilt of potatoes. Victorian Government. Retrieved April 10, 2025, from https://agriculture.vic.gov.au/biosecurity/plant-diseases/vegetable-diseases/bacterial-wilt-of-potatoes