Cassava rust

Cassava rust, caused by the fungus Uromyces manihotis, is a significant pathology affecting the cassava plant (Manihot esculenta). This obligate biotroph relies exclusively on its host to complete its lifecycle, which involves the formation of various spore stages typical of the Uredinales order. Its presence can severely impact the photosynthetic capacity of the plants.

The fungus colonizes the foliage, where it develops intercellular mycelia. As the pathogen matures, it produces pustules called uredinia. These structures erupt through the leaf epidermis, releasing a large number of urediniospores that serve as secondary inoculum, allowing the disease to spread rapidly throughout a field or across neighboring plantations.

Symptoms are most visible on the underside of the leaves, characterized by small, powdery pustules that are reddish-brown in color. The corresponding areas on the upper leaf surface often exhibit chlorosis or yellowing. In cases of severe infestation, infected leaves may dry out, curl, and abscise prematurely, which directly limits the plant's ability to store starch in its roots.

The development of Uromyces manihotis is highly dependent on favorable environmental conditions, particularly high humidity and moderate temperatures. Dew formation, persistent fog, or frequent rainfall significantly promote spore germination and infection. In tropical agriculture, these conditions are common, making the disease a persistent challenge for producers in affected areas.

• Planting resistant or tolerant cultivars to minimize susceptibility.
• Ensuring adequate spacing to promote better airflow and reduce leaf wetness.
• Removing and burying crop residues to decrease the primary inoculum source.
• Applying appropriate fungicides in commercial plantations if infection thresholds are met.
• Monitoring weather patterns to predict risk periods for rust outbreaks.