Onion yellow center rot pathogen

Pantoea allii is a Gram-negative bacterium that acts as a significant phytopathogen affecting various Allium species. Taxonomically, it belongs to the kingdom Bacteria, phylum Pseudomonadota, class Gammaproteobacteria, order Enterobacterales, family Erwiniaceae, and the genus Pantoea. It is recognized as a specific agent responsible for bacterial rot, causing substantial damage to commercial onion and garlic production globally.

The primary symptom associated with this pathogen is internal bulb decay, often referred to as center rot or bacterial soft rot. Infected plants exhibit discoloration and tissue maceration within the inner scales of the bulb. As the infection progresses, the tissues become water-soaked and mushy, frequently accompanied by an unpleasant odor, which signifies the breakdown of plant cell walls due to the pathogen’s enzymatic activity.

The biological cycle of the pathogen is highly dependent on environmental factors. Pantoea allii survives in crop debris, infested soil, and dormant within contaminated seeds or sets. Dissemination occurs through water splashing during rainfall or overhead irrigation. Furthermore, insects such as onion maggots and thrips play a crucial role as vectors, carrying the bacteria from infected tissues to healthy host plants during the growing season.

Optimal conditions for disease development include high humidity levels (typically above 85%) and moderate temperatures ranging from 20°C to 30°C. Heavy rainfall just before harvest is a critical factor, as it creates an environment conducive to the colonization of the bulb neck. If the neck does not dry out properly after harvest, the bacteria can easily travel down into the scales, leading to severe rot during post-harvest storage.

The economic impact is primarily observed in the form of heavy post-harvest losses and reduced marketability of the produce. Effective management requires an integrated approach:

• implementing long-term crop rotation;
• utilizing certified disease-free planting material;
• optimizing irrigation to minimize excessive foliage moisture;
• ensuring rapid and thorough curing of bulbs after harvest;
• maintaining low-humidity storage conditions to inhibit bacterial proliferation.