The bacteria formerly known as Erwinia carotovora are significant plant pathogens. They cause soft rot disease in a broad array of crops, leading to substantial losses in agricultural production globally, affecting both field-grown plants and harvested produce during storage.
Understanding the Bacterium
The bacterium formerly known as Erwinia carotovora has been reclassified into Pectobacterium and Dickeya, with Pectobacterium carotovorum being a prominent species. This gram-negative bacterium is facultative anaerobic, meaning it can survive with or without oxygen. It causes disease by producing pectolytic enzymes that break down pectin, which holds plant cells together. This leads to cell separation and soft decay. The bacterium is commonly found in soil and water environments.
Recognizing Plant Soft Rot
Soft rot caused by Pectobacterium carotovorum is characterized by a watery, mushy decay of plant tissues, often with a foul odor. Symptoms vary by plant part; tubers and roots may become entirely soft, while stems and leaves show localized lesions. Many agriculturally significant plants are susceptible, including potatoes, carrots, onions, cabbage, celery, and tomatoes. Ornamental plants can also be affected.
Factors Influencing Disease Development
Environmental conditions promote soft rot development and spread. High humidity, warm temperatures around 30°C (86°F), and inadequate air circulation create an ideal environment for bacterial multiplication. The bacterium spreads through contaminated soil and water, such as irrigation runoff or rain splash. Infected plant material like seeds, tubers, or cuttings also transmit the disease. Mechanical damage, insect feeding, or harvesting injuries create openings in plant tissues, providing entry points for the bacteria.
Managing and Preventing Soft Rot
Effective management of soft rot relies on preventive measures, as chemical treatments are not effective once the disease is established. Proper sanitation practices are fundamental, including thoroughly cleaning tools and equipment used in cultivation and promptly removing and disposing of infected plant debris to reduce the bacterial load in the environment.
Ensuring good drainage in fields and containers, along with adequate ventilation for stored crops, helps to reduce the high humidity levels that favor bacterial growth. Avoiding overwatering further minimizes the moist conditions conducive to disease development.
Implementing crop rotation with non-host plants, such as cereals or legumes, can help break the disease cycle by reducing the accumulation of the pathogen in the soil over time. Careful handling of plants during planting, cultivation, and harvesting is also important to prevent wounds that serve as entry points for the bacteria.
Using certified disease-free planting material, like healthy seeds or tubers, is a proactive step to avoid introducing the pathogen into fields. For harvested crops, storing them in cool, dry, and well-ventilated conditions significantly reduces the risk of post-harvest decay caused by soft rot bacteria.