Lasiodiplodiosis

The primary symptom is the development of necroses on trunks and branches. Affected bark tissue darkens, becomes depressed, and often cracks, exposing the underlying woody tissue.

Gummosis, or the oozing of sap from infected bark, is a common reaction to the pathogen's invasion. The exudate usually appears as a thick, dark-colored substance on the surface of the trunk or branches.

Vascular colonization leads to canopy dieback, leaf chlorosis, and wilting. Symptoms typically progress from the outer branches toward the main scaffold limbs of the tree.

When cutting into infected wood, internal staining or browning with distinct margins is often visible. Small, black pimple-like structures, known as pycnidia, may appear on the surface of the dead bark.

Severe infections eventually lead to the complete death of limbs and, in many cases, the entire tree if the pathogen encircles the main trunk.

The disease is caused by the fungus Lasiodiplodia pseudotheobromae, a member of the Botryosphaeriaceae family. It is a cosmopolitan polyphagous pathogen affecting a wide range of woody hosts in tropical and subtropical climates.

The fungus acts as an opportunistic pathogen that colonizes the bark and woody tissues of plants. Its life cycle involves both an asexual (anamorph) and a sexual (teleomorph) stage, which enhances its survival capacity.

The mycelium colonizes the plant's xylem and phloem, causing structural damage and interrupting nutrient transport. Spores are primarily disseminated by wind, rain splashes, and bark-boring insects.

This pathogen secretes specific enzymes and metabolites that induce systemic decay. The fungus is known to survive in a latent form within plant tissues, becoming active when the host plant is stressed or weakened.

Genomic plasticity of L. pseudotheobromae allows it to adapt quickly to different environmental stressors, making it an increasingly significant threat in changing climatic conditions.

The development of lasiodiplodiosis is favored by high temperatures and high humidity, with optimal growth occurring in ranges between +25°C and +30°C.

Environmental stress, such as drought, waterlogging, or mechanical injury, significantly increases host susceptibility. Open wounds serve as primary entry points for fungal spores.

Poor agricultural practices, such as excessive nitrogen fertilization, result in lush, soft growth that is more easily penetrated by the fungal mycelium.

High planting density restricts airflow and increases humidity within the canopy, creating an ideal microclimate for the pathogen to thrive and spread.

Bark-boring insects, such as beetles and weevils, are crucial vectors for the disease, carrying spores from infected to healthy trees and accelerating the spread of the infection.

The economic impact involves significant yield losses and the decline of orchard productivity. Infested trees require costly maintenance and frequent pruning of diseased limbs.

The disease disrupts normal physiological processes, leading to tree exhaustion. In commercial plantations, severe outbreaks often necessitate the removal of entire blocks of trees.

The pathogen remains viable in crop debris and woody residue, which creates a long-term reservoir of infection that is difficult to eradicate from the orchard environment.

Financial losses stem from reduced harvest quality and the ongoing expenses associated with fungicide applications and labor-intensive sanitation programs.

Infected trees are more susceptible to secondary invaders, further compromising the structural integrity and health of the plant until death becomes inevitable.

Sanitation is the most effective management strategy; this includes pruning and burning all symptomatic branches and infected wood to reduce the local inoculum.

Tools used for pruning must be disinfected with alcohol or other effective sanitizers between every cut to prevent the cross-contamination of healthy branches.

Optimizing irrigation and fertilization supports plant vigor and helps improve the tree's natural defenses against colonization by the fungus.

Preventive applications of copper-based fungicides can help protect wounds and reduce spore germination, especially during periods of high humidity or after physical damage.

Integrated pest management (IPM) focusing on the control of wood-boring insects is critical to prevent the dissemination of the fungus throughout the orchard.