Bacterial soft rot

Bacterial soft rot
Bacterial soft rot on a cabbage stalk
Scientific Classification
Kingdom:	Bacteria
Phylum:	Proteobacteria
Class:	Gamma Proteobacteria
Order:	Enterobacteriales
Family:	Enterobacteriaceae
Genus:	Pectobacterium
Species:	P. carotovorum
Synonyms
Bacterial black stalk Erwinia carotovora

Bacterial soft rot (Pectobacterium carotovorum) is a plant pathogen with a wide host range (carrot, potato, tomato, leafy greens (lettuce, perpetual spinach, cabbage, kale, etc.), squash and other cucurbits, onion, green peppers, etc.), able to cause disease in almost any plant tissue it invades. It is a very economically important pathogen in terms of postharvest losses, and a common cause of decay in stored fruits and vegetables. Most plants or plant parts can resist invasion by the bacteria, unless some type of wound is present. High humidity and temperatures around 30°C (86°F) favor development of decay.

Symptoms

Brassicaceae

Lower stem area will break during high wind or stress. Brown to orange area observed in latter stages. Strong putrid odor.

Carrot

An infected taproot has a soft and watery decay. The bacteria sometimes rapidly consume the entire taproot often leaving the epidermis (the peel) intact.

Allium

An infected bulb is pale-brown and, soft and watery. The infected plant appears healthy on the outside and when cut open some of the inner scales are brown, wet, and have a cooked appearance. The neck of the infected bulb is soft when pressed and emits a foul smell. The onion maggot is an important vector in carrying the bacteria from one plant to another and causing wounds for the infection to enter the bulb. Bacterial soft rot often occurs during storage.

Pepper

The infected fruits collapse and hang like water-filled bags.

Potato

An infected tuber has cream to tan colored tissues that are very soft and watery. The diseased area often has a black border separating it from a healthy one. The soft rot decay is generally odorless but becomes foul and slimy when other secondary bacteria invade the infected tissues. Soft rot bacteria can sometimes consume the entire tuber, leaving only its peel in the soil.

Prevention

Warm, wet conditions favor soft rot development. Therefore, select fields with good drainage. It is best to irrigate at night when dew is present.

Avoid high nitrogen rates with susceptible varieties. Increasing nitrogen does not increase the amount of disease with resistant varieties.

Surfactants, which are in most insecticides, also have been shown to increase soft rot severity. Therefore, get insects under control before soft rot begins to develop. If an insecticide must be used when soft rot is present, applications should be made when rain is not forecasted.

Finally, cut heads such that the stem stump is angled to permit water run-off. Water pooling on a flat stump will provide favorable conditions for soft rot. Bacteria in rotting stem stumps can be dispersed to heads not yet harvested.

Hosts

Potential pathogen hosts include:

• Cabbage
• Carrot
• Celery
• Chicory
• Onion
• Potato
• Radish
• Tomato

Examples

Cucurbit

Cabbage

Onion

Potato

Sweetcorn