Diplodia root and stem rot of cassava

Early symptoms include wilting of the foliage, which typically starts from the lower leaves and progresses upward until the entire plant dies.

Inspection of the roots reveals dark, discolored areas that eventually develop into deep, dry rot, consuming the starchy interior of the tubers.

Small black dots, representing the fungal pycnidia, may be visible on the surface of the stems, indicating the active sporulation phase.

When infected roots are sliced, the internal tissue shows significant decay, often accompanied by a musty odor and gray or white fungal growth.

The total degradation of the root system causes the plant to lose its anchoring, leading to premature plant collapse in the field.

The disease is caused by the fungus Diplodia manihotis, which belongs to the class Ascomycetes. This pathogen is known for its persistence in the soil and on crop debris for extended periods.

The fungus invades the vascular system of the cassava plant, typically entering through physical injuries on roots or stems caused by agricultural activities.

It produces pycnidia which release conidia, the primary inoculum for infection, spread by rain splashes, wind, and contaminated farming equipment.

The biological cycle of the pathogen is closely tied to decaying plant matter, which serves as a long-term reservoir for the fungus.

Cassava is the primary host, and the continuous cultivation of the crop on the same site often leads to a heavy build-up of the fungal inoculum.

The disease thrives in conditions of high soil moisture and moderate temperatures, which are optimal for the growth of the fungal mycelium.

Heavy clay soils with poor drainage are particularly susceptible, as water stagnation creates an environment where root rot can easily initiate.

Physical trauma to the roots caused by weeding or insect pests provides entry points that facilitate the colonization of healthy tissue by the fungus.

Dense planting patterns that limit air circulation around the base of the plant allow moisture to persist, encouraging the spread of the disease.

Periods of heavy rainfall combined with high humidity significantly accelerate the life cycle of Diplodia manihotis and the infection rate.

Diplodia root rot causes significant economic losses by destroying the tuberous roots, which are the main marketable part of the cassava crop.

Harvested products from infected fields have poor quality and a very short shelf life, making them unsuitable for processing or human consumption.

Severe outbreaks can result in substantial yield reductions, threatening the food security and income of smallholder farmers in affected regions.

The use of infected stems as planting material ensures the transmission of the fungus to new fields, spreading the disease geographically.

The weakening of the plant's immune system makes it highly susceptible to a complex of secondary pathogens, leading to complete crop failure.

The most critical control measure is the use of healthy, disease-free cuttings to ensure that the initial planting material is not contaminated.

Implementing a rigorous crop rotation strategy helps to reduce the concentration of fungal spores in the soil, preventing persistent infection.

Sanitation practices, such as the removal and destruction of crop residues, are essential to eliminate the primary sources of the fungus.

Improving soil drainage and optimizing irrigation schedules prevent waterlogging, which is a key trigger for the development of Diplodia rot.

• Regular cleaning of farm tools to prevent pathogen transfer.
• Selecting cassava varieties with known resistance or tolerance.
• Managing soil-borne pests to prevent root tissue damage.