Cacao pod rot

Phytophthora botryosa is a pathogenic oomycete responsible for a serious disease affecting cacao pods (Theobroma cacao). While often overshadowed by other Phytophthora species, this pathogen is recognized for its significant impact on cocoa production in specific tropical regions, particularly in Southeast Asia, where it thrives under high-moisture environmental conditions.

The primary host for this pathogen is the cacao tree. The infection manifests as black pod rot, a devastating condition that can affect the pods at any stage of development. From young cherelles to mature pods, the pathogen can infiltrate the fruit, causing tissue necrosis and drastically reducing both the quality and quantity of the harvestable cocoa beans.

Initial symptoms include the appearance of small brown spots on the pod surface. These spots enlarge rapidly, turn dark brown or black, and eventually spread over the entire pod. Under high humidity, a characteristic white or grayish fungal-like mat of sporangia may appear on the surface. Internally, the infected tissues become soft and necrotic, quickly decomposing into a mass of decayed material.

The disease spreads primarily through zoospores, which are dispersed by rain splash, wind-blown water droplets, and potential insect vectors. Epidemics are favored by heavy rainfall, high relative humidity, and warm temperatures. In dense canopy environments where air circulation is poor and humidity remains trapped, the conditions for the rapid multiplication and spread of P. botryosa are optimal.

Management of the disease requires an integrated approach to maintain plantation health. Key preventative measures include the following:

• Regular pruning of cacao trees to improve airflow and reduce canopy humidity.
• Frequent and thorough harvesting to remove and destroy infected pods from the trees and ground.
• Selecting and breeding for resistant cacao genotypes.
• Application of copper-based fungicides during the rainy season to provide a protective barrier against spore germination and infection.