Diaporthe wilt of annonas

The first noticeable sign of the disease is a sudden loss of turgor in the leaves. This usually starts on individual branches and can rapidly spread to the entire canopy of the tree.

Affected bark typically exhibits localized necrotic lesions or cankers. These areas may appear sunken, and the bark often cracks, revealing the underlying damaged wood.

A cross-section of an infected branch shows distinct discoloration of the cambium and xylem, which become dark brown or greyish due to the systemic spread of the fungal hyphae.

Under humid conditions, small black pimple-like structures, which are the pycnidia of the fungus, emerge through the epidermis of the dead or dying bark to release new spores.

As the disease progresses, the tree shows signs of general decline, including stunted growth, leaf chlorosis, and the eventual dieback of peripheral twigs and branches.

The causative agent of this disease is the ascomycete fungus Diaporthe annonacearum. It is a specialized pathogen that primarily targets species within the Annonaceae family.

The fungus survives in infected plant tissues, crop debris, and soil as mycelium or as fruiting bodies such as perithecia and pycnidia, waiting for favorable conditions to proliferate.

During the growing season, the pathogen produces spores that are easily disseminated by wind, rain splashes, and movement of insects or machinery within the orchard.

Infection is facilitated by entry through natural openings, bark fissures, or wounds created by pruning and harvesting operations, allowing the fungus to colonize the vascular tissues.

Once inside the plant, the fungal mycelium colonizes the xylem, obstructing the flow of water and nutrients, which results in the characteristic wilting symptoms observed in mature trees.

High humidity, frequent rainfall, and moderate temperatures provide optimal conditions for the growth and sporulation of Diaporthe annonacearum in the field.

Orchards with high planting densities or poor air circulation are particularly vulnerable, as trapped moisture on leaf surfaces and twigs promotes rapid fungal infection.

Physical injuries to the tree, caused by inclement weather or improper pruning practices, act as primary entry points for the fungus, especially when wounds are not treated.

Trees undergoing physiological stress due to poor soil management, nutrient deficiencies, or drought are significantly more susceptible to infection by this pathogen.

The movement of contaminated pruning tools from infected trees to healthy ones is one of the most common ways the disease spreads through an orchard environment.

Diaporthe wilt poses a severe threat to commercial annona cultivation, including cherimoya and sugar apple, as it causes significant tree mortality.

The disease leads to a drastic reduction in productivity; fruit on infected branches often fails to mature, resulting in significant yield loss and economic hardship for growers.

The systemic nature of the infection makes it difficult to manage once it reaches the main trunk, often necessitating the removal of the entire tree to prevent further spread.

In addition to direct losses, the disease diminishes the overall lifespan and vigor of the orchard, requiring investment in replanting and long-term sanitation measures.

Uncontrolled spread of the pathogen can lead to the total collapse of a plantation if early intervention strategies are not implemented effectively.

Strict orchard sanitation is the cornerstone of management. All infected branches must be pruned back to healthy wood and immediately destroyed by burning.

Disinfection of pruning equipment is essential; tools must be cleaned with alcohol or appropriate bleach solutions after each tree to prevent cross-contamination.

Maintaining an open canopy through proper pruning helps improve airflow, which keeps the foliage dry and creates an environment less conducive to fungal development.

Preventive fungicide applications, particularly during high-risk seasons with heavy rain, can help protect healthy trees from initial infection by the pathogen.

• Use certified disease-free nursery stock.
• Ensure adequate fertilization to boost plant immunity.
• Manage bark-boring pests that create entry wounds.
• Maintain weed-free zones around the base of trees.