Erwinia rhapontici

Erwinia rhapontici is a gram-negative, rod-shaped bacterium classified within the Enterobacteriaceae family. It is a significant phytopathogen responsible for causing bacterial decay in various crops, most notably observed in onions, rhubarb, and occasionally other horticultural plants.

The disease caused by this pathogen is widely known as pink rot of onions. The hallmark symptom is the internal discoloration of the bulb scales, which take on a distinct pinkish hue. This condition often develops internally, making it difficult to detect during harvest and leading to significant post-harvest losses and degradation of market quality.

The biology of the pathogen revolves around its survival in soil, crop debris, and contaminated propagation material. The bacterium acts as an opportunistic pathogen, entering plant tissues through wounds caused by mechanical damage or insect feeding. Once inside, it secretes extracellular enzymes that break down plant cell walls, leading to tissue softening and necrosis.

Environmental conditions play a pivotal role in the disease cycle. High humidity and temperatures ranging from 20°C to 28°C facilitate rapid bacterial multiplication. In storage facilities, inadequate ventilation and condensation allow the bacteria to spread rapidly from infected bulbs to healthy ones, potentially compromising an entire stock within a few weeks.

Effective management and control of Erwinia rhapontici rely heavily on preventative agronomic practices rather than chemical treatments. Key strategies include:

• Implementing strict crop rotation to reduce soil-borne inoculum levels.
• Ensuring the use of high-quality, disease-free planting material.
• Minimizing physical damage during harvesting and transportation.
• Providing adequate drying (curing) of bulbs immediately after harvest.
• Maintaining optimal storage conditions with low humidity and high air circulation.