Pink root in onion plant

Disease name: Pink root of onion plant

The scientific name: Phoma terrestris

Type of disease: fungal

Disease family: Phaeosphaeriaceae

(The first symptoms of infection appear, as the color of the onion roots changes)

• The causes of disease:

The fungus Phoma terrestris causes pink root disease, which attacks onion roots directly without the need for a vector. It can also remain in the soil for long periods and feed on plant remains.

• Symptoms of the disease:

The initial symptoms of the disease appear one to two weeks after infection, and the most prominent of these symptoms is the change in the color of the roots to pink, then they turn to dark red or purple, they begin to dry out, and in the end the roots die, which leads to the onion leaves falling and the fruits being stunted.

(Plants affected by pink root disease are stunted)

• Disease development cycle:

The fungus can penetrate directly into onion roots without the need for wounds. The fungus also spreads through irrigation water to areas not infected with the fungus, and the severity of the disease is higher in fields with heavy, poorly drained soil.

(Onion roots change color to purple as a result of infection with the pink root fungus)

• Conditions suitable for the spread of the disease:

Plant stresses such as drought, cold, nutrient deficiency, insects, and other diseases increase the severity of the disease by weakening the plant’s ability to resist the fungus. The fungus is most active at temperatures ranging between 23-27 degrees Celsius.

• Losses resulting from the spread of the disease:

Yield losses are greatest when plants are infected early in the season, resulting in a weak root system that cannot keep up with water absorption during high temperatures, causing significant impairment in crop production.

• Control:

1. Chemical control: Fumigating the soil using metam sodium or chloropicrin helps get rid of fungi present in the soil. In case of severe infestation, fungicides can be used.
2. Organic control: removing infected parts and disposing of them away from the field.

• preventive measures:

1. Use disease-resistant varieties.
2. Avoid planting in soil infected with the disease.
3. Good fertilization helps enhance the plant’s resistance to disease.
4. Sterilize agricultural tools before use.
5. Providing a good irrigation and drainage system to prevent a suitable environment for the disease.

(Weak root system in the affected plant compared to the healthy plant)

• Sources:
• https://extension.usu.edu/pests/ipm/notes_ag/veg-pink-root-of-onion