Bacterial soft rot

Pantoea ananatis

This bacterium can help or hinder plants. Scientists are still learning about about its effects but we do know that it is harmful to many crops that are important to New Zealand.

About bacterial soft rot

These bacteria can cause disease in onions, eucalyptus, tomatoes, melons, maize, and other plants. There are different strains of the bacteria. Some can be helpful, some harmful, and some harmless. Scientists are still learning about the benefits and risks of the different strains of bacteria.

Global distribution of bacterial soft rot

World map showing distribution of bacterial soft rot.

Why this is a problem for New Zealand

The bacteria have caused serious crop losses overseas. They can cause diseases such as:

  • stalk rot, bacterial wilt, and leaf blight in maize
  • bacterial leaf blight and shoot tip dieback in 2 types of eucalyptus
  • centre rot in onions
  • grey wall in tomatoes
  • internal rot in melons.

How it could get here

Map of New Zealand showing where bacterial soft rot could establish

Infected plant material, seeds, or soil are the most likely pathways for the bacteria to enter New Zealand.

There are 2 species of thrips that could transmit the bacteria between plants. Thrips are tiny insects that feed on plants. The thrips eat infected material and pass it on to otherwise healthy plants.

Biosecurity New Zealand has strict measures in place to limit the chances of Pantoea ananatis making it through the border in plants or thrips.

How to identify infection

The signs of a Pantoea ananatis infection can be similar to other diseases. Diagnosis requires an expert. The severity of these diseases can vary depending on conditions, like humidity and temperature.

Leaf with straw colored streaks and an irregular streak with a brown edge Onion bulb cut open with rotten outer layers
Left: Sudangrass leaf with symptoms.  Image: CC 3.0 Gerald Holmes,  
Right: Onion cut open to show damage from bacterial blight. Image: CC 3.0 Howard F. Schwartz,

If you find signs of the diseases

If you're an experienced grower of the host plants and have found an unusual disease in your plants:

Note: This information is a summary of this disease's global distribution and potential impacts on New Zealand. 

Last reviewed: