Pink root of onion

This pathogen is specialized in attacking the root systems of Allium species. Its ability to remain viable in the soil in the absence of a host makes it a persistent threat that requires complex management strategies to control its population effectively.

Onions are the primary host, but the fungus also infects leeks, garlic, shallots, and various grass species. When the roots are colonized, they lose the ability to absorb water and nutrients, leading to systemic stress throughout the plant.

Significant damage occurs during the growth phase, leading to stunted plants and smaller bulbs. Because the roots are damaged, the plants become increasingly susceptible to secondary infections and cannot tolerate periods of drought or nutrient stress.

The fungus thrives in warm soil temperatures, with the optimal range being between +24°C and +28°C. Consequently, the disease is most prevalent during the warmer months of the growing season when environmental conditions favour rapid fungal colonization.

Although it can infect plants at any growth stage, the visible symptoms often peak as temperatures rise and the plants reach maturity. Excessive soil moisture combined with warmth accelerates the infection process, allowing the fungus to spread rapidly.

The characteristic symptom is the development of a pinkish discoloration on the roots, which eventually turns purple, brown, or black as the tissue dies. Infected roots become brittle, rot, and eventually disintegrate, leaving the plant with a severely compromised root system.

Above-ground symptoms include progressive yellowing and drying of the leaf tips, often misidentified as drought stress or nutrient deficiency. Plants can be easily pulled from the soil because the root system is incapable of anchoring them properly due to extensive rot.

The primary control strategy involves long-term crop rotation, specifically avoiding Allium crops for at least 4 to 6 years. Implementing good irrigation management to prevent water-logged soils is also crucial in reducing the severity of root infection.

• Selection of resistant or tolerant onion cultivars and hybrids.
• Improving soil drainage to minimize the conditions favourable for fungal growth.
• Proper sanitation, including the removal of crop debris after harvest to reduce inoculum.
• Balanced fertilization to support root growth and improve plant immunity.
• Use of soil fungicides as a preventive measure in highly infested fields, following agronomic guidelines.