Pathogen Profile: Pectobacterium carotovorum 

lettuce soft rot

Becky Anderson Science Communicator

Written by: Becky Anderson

Published by: David Santos

What is Pectobacterium carotovorum?

Pectobacterium carotovorum is one pathogen, of many, that causes soft rot in plants. It is a Gram-negative, rod-shaped, facultative anaerobe [1], (Figure 1). This bacteria is part of the order Enterobacterales [2] which includes other well-known bacteria such as Escherichia coli, Klebsiella pneumoniae and Salmonella, to name a few. Soft rot is a devastating and costly disease, causing a loss of approximately 46 million euros in the European potato industry, each year [3]. Although potatoes are the most common targets of Pectobacterium soft rot, other plant species, including hydroponically grown plants can become infected: banana, cabbage, capsicum, carrot, celery, lettuce (Figure 2), potato, spinach, cucurbits, and tomato. Host plants specific for P. carotovorum are summarized in Table 1.

Facultative anaerobe – bacteria which can grow with or without oxygen

Gram stained growing Pectobacterium carotovorum
Figure 1. Gram stain of Pectobacterium carotovorum cells, using a light microscope with 100x magnification. Sourced from Niemi et al., 2017.

In addition to causing soft rot in a variety of plants, the genus Pectobacterium can cause other diseases depending on the host, including blackleg in potatoes, bleeding canker in pears and foot rot in rice [4]. However, the species P. carotovorum does not cause disease other than soft rot.

bacterial soft rot
Figure 2. Soft rot in potatoes caused by Pectobacterium carotovorum (Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org)

Table 1. A list of host plants for Pectobacterium carotovorum and their common name

Taxonomic Identification

Common Name

Abelmoschus esculentus 

Okra

Artemisia absinthium

Wormwood

Brassica oleracea

Cabbage

Cichorium intybus

Chicory

Citrullus lanatus

Watermelon

Cucumis sativus

Cucumber

Cynara cardunculus

Cardoon/artichoke thistle

Chamaecereus silvestrii

Cactus

Fritillaria imperialis

Crown Imperial

Haworthia

Succulent

Ipomoea batatas

Sweet potato vine

Kalanchoe tubiflora

Succulent

Lactuca sativa

Lettuce

Opuntia spp.

Prickly pear cactus

Orostachys spp.

Succulent

Papaver somniferum

Poppy

Peperomia spp.

Peperomia

Plectranthus australis

Swedish Ivy

Pilea cadierei

Aluminum plant

Pinellia ternata

Cow dipper

Rheum rhabarbarum

Rhubarb

Silybum marianum

Thistle

Saintpaulia ionantha

African Violet

Solanum sp.

Potato, tomato, eggplant

Spathiphyllum wallisii

Peace lily

Typhonium giganteum

Voodoo lily

The information in this table is adapted from Charkowski, 2018.

Soft rot can also be caused by other species of Pectobacterium and species of the genus Dickeya. Both Pectobacterium and Dickeya genera were originally referred to as Erwinia but over the last 20 years and taxonomic changes, they were denoted as two individual separate genera, with numerous species [4].


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Infection and Symptoms:

Pectobacterium carotovorum is an environmental bacteria. P. carotovorum is typically an issue for farmers and growers when it colonizes irrigation water or in the case of hydroponic systems, the source of water and plumbing used for the aqueous growth solution. On some surfaces, P. carotovorum can form biofilms [5] which makes it even more difficult to eradicate from plumbing lines. 

Pectobacterium causes soft rot by targeting the leaves and the stems of plants. The disease appears as a “water-soaked”, large, brown, slimy spot (Figure 3). The rotting will start from the outside layers of the plant and work its way in. Infection usually starts from a wound, or a break in plant tissue, which can be on the roots, stem, leaves or fruiting body. 

lettuce soft rot
Figure 3. Soft rot caused by Pectobacterium carotovorum on the surface of lettuce. Image sourced from https://apps.lucidcentral.org/pppw_v10/text/web_full/entities/lettuce_soft_rot_289.htm
pectobacterium on cabbage
Figure 4. A cross-section of infected lettuce to show how deep the disease spreads. Image sourced from https://apps.lucidcentral.org/pppw_v10/text/web_full/entities/lettuce_soft_rot_289.htm

Growth Conditions:

Pectobacterium carotovorum is a soilborne pathogen with an optimal growth range of 20 to 25°C. However, due to its biochemical properties, it can also grow at 37˚C and in high salt concentrations of 5% NaCl [1]. Additionally, this bacteria thrives in wet and humid conditions. This pathogen’s tolerances to high temperatures and salt thresholds, along with the preference for damp conditions can make it difficult to control in hydroponic systems.

Preventing Pectobacterium carotovorum infection:

Due to the ubiquity of this pathogen, it is hard to avoid entirely but steps can be made to reduce the likelihood and severity of infection:

  1. Use clean and properly disinfected tools to avoid introducing the pathogen to the plants.
  2. Avoid pooling water, especially in contact with plants to prevent contamination and the likelihood of infection. 
  3. Ensure there is proper air circulation and dehumidification to reduce the prevalence of the pathogen if present in the environment. 

Although Pectobacterium species are mostly found in soil, they can hitch a ride on infected and imported tools, as well as seeds. 

Controlling Pectobacterium carotovorum infection

Unfortunately, once crops start displaying symptoms of soft rot, there is no cure for the disease. However, biocontrol methods using phages have shown promising effects at controlling and preventing diseases caused by Pectobacterium and Dickeya before they start [6].

Phages – also known as bacteriophages, are viruses which specifically target bacterial cells. 

Since many different pathogens cause soft rot disease, it is necessary to identify the cause of disease in a lab. Unfortunately, if you have a confirmed Pectobacterium infection causing soft rot in your plants, you need to properly dispose of the infected crops. It is also recommended that you properly disinfect the area and anything that was in contact with the infected crops. 

The good news is, that Pectobacterium carotovorum is one of the bacterial species that we can detect using Pathogen+, a microbial surveillance service. Contact us at [email protected] to get started or to learn more about which program will best suit your needs. 

Disclaimer:

The information we present in Pathogen Profile is based on collating published peer-reviewed scientific literature and sources we think are reliable. This is by no means an exhaustive review of pathogens. Pathogen Profile gives a small glimpse of what is known about pathogens and we encourage growers to do more research on their own based on the pathogens in relation to their own crops and hydroponic systems. The information presented in Pathogen Profile is for educational purposes and should not be used as professional advice to treat pathogens or to operate your hydroponic system.

Works Cited

  1. Bosmans, L., Moerkens, R., Wittemans, L., De Mot, R., Rediers, H. and Lievens, B. (2017), Rhizogenic agrobacteria in hydroponic crops: epidemics, diagnostics and control. Plant Pathol, 66: 1043-1053. https://doi.org/10.1111/ppa.12687
  2. Conn, H.J. Validity of the genus Alcaligenes. J Bacteriol 44:353–360; 1942 doi: 10.1128/jb.44.3.353-360.1942
  3. Veena, V., Taylor, C.G. Agrobacterium rhizogenes: recent developments and promising applications. In Vitro Cell.Dev.Biol.-Plant 43, 383–403 (2007). https://doi.org/10.1007/s11627-007-9096-8
  4. Yasybaeva G, Vershinina Z, Kuluev B, Mikhaylova E, Baymiev A, Chemeris A 2017 Biolistic-mediated plasmid-free transformation for induction of hairy roots in tobacco plants. Plant Root 11:33-39. doi:10.3117/plantroot.11.33 Copyrights 2017, Plant Root (JSRR), www.plantroot.org (https://www.cabdirect.org/cabdirect/abstract/20183132574
  5. Brenner, DJ., Krieg, NR., Staley, JT,. “Bergey’s Manual of Systematic Bacteriology: The Proteobacteria Part C”. Vol.2. Springer. 2005. 340-345.
  6. Weller SA, Stead DE, Young JPW, 2006. Recurrent outbreaks of root mat in cucumber and tomato are associated with a monomorphic, cucumopine, Ri-plasmid harboured by various Alphaproteobacteria. FEMS Microbiology Letters  25813643. https://doi.org/10.1111/j.1574-6968.2006.00214.x
  7. John R. Porter Ph.D. & Hector Flores Ph.D. (1991) Host range and implications of plant infection by Agrobacterium rhizogenes, Critical Reviews in Plant Sciences,10:4, 387-421, DOI: 10.1080/07352689109382318
  8. Dannehl, D., Suhl, J., Ulrichs, C., y Schmidt, U. (2015). Evaluation of substitutes for rock wool as growing substrate for hydroponic tomato production. Journal of Applied Botany and Food Quality, 88(1). DOI:10.5073/JABFQ.2015.088.010
  9. Gutierrez-Valdes N, Häkkinen ST, Lemasson C, Guillet M, Oksman-Caldentey K-M, Ritala A and Cardon F (2020) Hairy Root Cultures—A Versatile Tool With Multiple Applications. Front. Plant Sci. 11:33. DOI: 10.3389/fpls.2020.00033
  10. Suresh, B.; Ravishankar, G.A. Phytoremediation—a novel and promising approach for environmental clean-up. Crit Rev Biotechnol 24:97–124; 2004. DOI: 10.1080/07388550490493627

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