Pink rot

Pink rot is a fungal disease affecting various plants, most notably potatoes, celery, and onions, both in the field and during post-harvest storage. It is caused by several species of fungi, primarily Phytophthora erythroseptica, but other Phytophthora species and sometimes Pythium species can also be involved.

Symptoms:

The most characteristic symptom of pink rot is a soft, watery rot that develops in the affected plant tissue. In potatoes, the decay usually begins at the stolon end and progresses upwards. When cut open, the flesh exhibits a light pink to salmon-colored discoloration, which darkens upon exposure to air, eventually turning black or grey. The affected tissue is typically rubbery and has a distinct vinegar-like odor.

In celery, pink rot causes a soft, watery decay at the base of the stalks. The affected area becomes pinkish or reddish.

Onions can also be affected, showing a similar soft rot, frequently accompanied by a pinkish discoloration.

Disease Cycle:

Phytophthora erythroseptica is an oomycete, a fungus-like organism that thrives in wet conditions. The fungus can survive in the soil as oospores or sporangia for extended periods. Infection occurs when these structures germinate in the presence of susceptible plant tissue and sufficient moisture. Zoospores, motile spores released from sporangia, can swim to and infect plant roots or tubers. Wounds can facilitate entry of the pathogen. The disease is favored by warm temperatures and high soil moisture levels.

Management:

Control of pink rot relies on a combination of preventative measures:

• Crop Rotation: Rotating to non-host crops helps reduce the buildup of the pathogen in the soil.
• Soil Drainage: Improving soil drainage reduces soil moisture, making conditions less favorable for the fungus.
• Proper Harvesting: Avoiding bruising and wounding during harvest reduces entry points for the pathogen.
• Sanitation: Removing and destroying infected plant debris helps prevent the spread of the disease.
• Fungicides: Fungicides containing active ingredients effective against oomycetes, such as metalaxyl or mefenoxam, can be applied as soil treatments or foliar sprays to protect susceptible plants.
• Resistant Varieties: Utilizing potato varieties with some resistance to pink rot can help to minimize losses.
• Post-Harvest Handling: Proper ventilation and storage at cooler temperatures help to slow the development of pink rot after harvest.