Pink root

Pink root, caused by the fungus Setophoma terrestris, is a significant soil-borne disease that severely affects root systems of onion, garlic, and watermelon. As a persistent pathogen, it thrives in soil residues and can survive in the environment for many years, making it a persistent threat to commercial vegetable production.

The disease specifically targets the root tissue, entering through the root hairs and epidermal layers. Once established, the fungus colonizes the root system, severely impairing the plant's ability to absorb water and essential mineral nutrients, leading to stunted plant growth and significant yield loss.

Visual diagnostic signs are characteristic: roots display a distinct color shift from white to pink, then to deep purple or dark magenta. Eventually, the infected roots turn necrotic, becoming brittle and turning black as they decay, which often causes the entire plant to wilt prematurely during the peak of the growing season.

The development of pink root is strongly correlated with warm soil temperatures, generally between 24°C and 28°C. Poorly drained soils, over-irrigation, and continuous monocropping of susceptible species drastically accelerate the population growth of Setophoma terrestris in the field, leading to rapid disease transmission.

Management strategies focus on long-term prevention since direct chemical curative methods are limited. Key control practices include:

• Practicing extended crop rotations (4–6 years) with non-host crops.
• Selecting genetically resistant onion and garlic cultivars adapted to the region.
• Improving soil aeration and drainage to reduce moisture stress.
• Treating seed and sets with professional fungicides before planting to protect early development.