Diplodia root and stem rot of cassava

Diplodia root and stem rot is a fungal plant disease caused by the pathogen Diplodia manihotis. This disease specifically impacts cassava (Manihot esculenta), often resulting in severe yield losses during cultivation and significant post-harvest degradation of the starchy tubers.

The causal agent is a fungus that acts as a necrotrophic pathogen, colonizing the host tissues and causing rapid necrosis. The infection typically begins when fungal spores or mycelia enter the plant through wounds caused by tools, insects, or environmental stress, such as soil saturation or drought-induced root cracks.

Symptoms of the infection include the discoloration of root tissues, which transition from a healthy cream color to a dark, watery rot. On the exterior surface of the tubers and stems, the fungus produces small, black, dot-like fruiting bodies called pycnidia. As the rot progresses, the internal tuber tissue breaks down completely, often leading to a total loss of the crop.

The development and spread of Diplodia manihotis are heavily influenced by environmental factors. High soil moisture and warm temperatures create ideal conditions for the pathogen to thrive. Furthermore, the spread of spores is facilitated by wind, splashing rain, and the movement of contaminated soil or infected planting materials between fields.

Management and prevention focus on integrated cultural practices rather than chemical treatments. Key strategies include selecting resistant cassava varieties, ensuring soil drainage to prevent waterlogging, and practicing crop rotation to reduce inoculum levels in the soil. Furthermore, post-harvest losses can be significantly minimized by ensuring rapid drying of tubers and storage in cool, well-ventilated conditions.