Pink root rot: Infected roots of onion
Pathogen: Phoma terrestris (syn. Pyrenochaeta terrestris)
Symptoms
Infected roots show a light pink color that become deeper pink or red with time and finally purple-brown as the roots shrivel and disintegrate. New roots may continue to form and then be killed by the fungus.
Disease development
Fungus can survive in the soil, in diseased roots and the debris of susceptible crops for several years. The fungus can be spread through soil movement and in irrigation water. This disease can develop at all soil moisture levels that allow onion growth. Optimum temperatures for growth of the pathogen and disease development are 24-28°C.
Disease management
Resistance to the pathogen varies among cultivars, thus resistant cultivars should be planted when possible. Resistance may be overcome if soil temperatures of 28°C (82°F) or higher occur. Planting so the bulk of the root growth occurs prior to reaching soil temperatures that favor disease development can minimize severe losses from this disease. Long term rotation (4-6 years) with non-host crops, such as cereals, helps reduce losses. Also, soil solarization or fumigation can help to reduce pink root and increase marketable bulbs.
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