Pink root

Pink root is a destructive plant disease caused by the soil-borne fungus Pyrenochaeta terrestris. It is recognized as one of the most common and persistent diseases affecting root systems globally. The fungus thrives in soil for extended periods, remaining dormant as sclerotia until favorable conditions and a suitable host plant allow it to resume its life cycle.

The pathogen has a wide host range, posing a threat to various economically important crops. Most commonly, it affects onions and garlic, causing significant economic damage. However, it is also known to infect other crops including oats, winter rapeseed, turnips, watermelons, strawberries, and soybeans. This wide host range makes management through crop rotation particularly challenging.

The symptoms of pink root are distinct and easily identifiable. Infected roots initially show a light pink discoloration, which eventually turns dark red or purple, and finally brown or black as the roots die and decay. As the root system loses its ability to absorb water and nutrients, the leaves begin to yellow, tip-burn, and wither, causing the plant to remain stunted and yield poorly.

Development of the fungus is highly temperature-dependent, with optimal growth occurring at soil temperatures between 24 °C and 28 °C. Warmer conditions significantly accelerate the infection process. Spread of the pathogen occurs via contaminated soil transport, irrigation runoff, infested farm equipment, and the planting of infected sets or transplants, which can introduce the fungus into previously clean fields.

Management strategies must be multi-faceted to be effective. Key preventive measures include selecting resistant cultivars, implementing long crop rotation cycles (minimum 4–6 years), and maintaining excellent soil fertility to support vigorous root growth. Additionally, avoiding over-irrigation during high temperatures and utilizing soil solarization or chemical fumigation in greenhouse environments can help reduce inoculum levels and mitigate disease impact.