Bacterial Soft Rot

Causal Organism: Pectobacterium carotovora subsp. carotovora; P. carotovora subsp. atroseptica; other species (Bacillus, Clostridium, Flavobacterium, Pseudomonas) – formerly called Erwinia

Crops Affected: potato and a wide range of root, fruit, and leafy vegetables (e.g. carrot, cabbage, onion, tomato); may also affect other crops and plants

Disease Cycle:

• Bacterial pathogen
  • It can survive for several months in the soil
  • It can be dispersed by irrigation water or other water movement
• A wound is required for tissues to be invaded
  • This may be from mechanical, environmental, or other pathogen or insect pest damage
  • It may occur at a wound, bruise, or other entry point
• Immature or overripe tissues are more susceptible than mature tissues
• The pathogen may spread between plants during storage, transportation, or in wash water during post-harvest handling

Conditions that Favour Disease Development:

• Disease development is favoured by high temperatures and moist conditions, with in terms of soil moisture or high humidity
• Poor ventilation and high humidity or wet tubers in packaging can encourage the disease
• Frozen tubers (damage) or harvesting under wet conditions can increase disease incidence

Symptoms:

• The disease often forms as a secondary rot to other diseases
  • The primary invader damages the produce, allowing bacterial soft rot to infect and develop
• Rots are typically restricted to tubers, roots, or fruit tissues rather than actively growing tissues
• Initial symptoms may include small, water-soaked lesions or sunken brown lesions around a wound or entry point
  • Lesions may quickly enlarge and grow together, with tissues becoming watery and mushy
  • Infected tuber tissues are cream-coloured and become brown, slimy, and stinky
    • A foul odor is common with bacterial pathogens, as secondary compounds produced by the bacteria have an odor
  • Diseased tissues are sharply delineated from healthy tissues
  • Infected tissues may ooze or leak out onto other healthy product

Management:

• Grow crops in well-drained soils
• Maintain an adequate crop rotation
• Harvest only mature products
• Minimize bruising and wounding during harvest and all post-harvest activities
• Control other diseases and insects that create wounds or weak points
• Store crops at as cool a temperature as possible (without causing other issues)
  • Cooler temperatures will slow harvested produce aging and degradation, reduce infection, and potentially slow disease development if it occurs
• Ensure wash water is properly disinfected (chlorine or ozone) and is changed frequently
  • Avoid soaking produce for long periods
• Only package cooled product
  • Dry product before packaging
• Disinfect equipment and storages periodically if soft rot is a consistent issue