Pink root rot

Pink root rot is a devastating soil-borne disease caused by the fungus Pseudopyrenochaeta terrestris. This pathogen primarily attacks the root system, severely impeding the plant's ability to uptake water and nutrients. The fungus is highly persistent in the soil, surviving for many years as sclerotia even in the absence of a host plant, making it a difficult pathogen to eradicate.

The disease primarily affects members of the Alliaceae family, with onions, shallots, garlic, and leeks being the most susceptible. While it is most economically damaging in onion production, the fungus can also colonize the roots of various cereal crops, grasses, and other vegetables, allowing the pathogen to maintain a stable population density within the soil ecosystem.

The primary diagnostic symptom is the development of a pink discoloration on the roots, which gradually darkens to a reddish-purple, dark brown, or black color as the tissue dies and rots. Above-ground, infected plants show stunted growth, leaf chlorosis, and tip dieback. As the root system loses its function, the plant becomes increasingly susceptible to drought stress and eventually dies.

Temperature is a critical factor in the development and spread of Pseudopyrenochaeta terrestris. The disease is most aggressive in warm soil conditions, typically between 24 °C and 28 °C. Moisture availability also plays a significant role in pathogen spread, as spores can be moved through the soil by irrigation water, rainfall, or tillage equipment during field operations.

The impact of pink root rot is significant, leading to reduced bulb size, lower market yields, and poor storage quality for the affected onions. In severely infested fields, the pathogen can cause complete crop failure if susceptible varieties are grown. Management relies heavily on cultural practices, as chemical control options are often limited and expensive once the pathogen is established in the soil.

• Implementing long-term crop rotation (5 years or more).
• Selecting and planting resistant onion varieties and hybrids.
• Managing soil moisture to reduce stress on plants.
• Maintaining high soil fertility to support root regeneration.
• Using soil solarization or chemical fumigation in high-value production systems.