Stigmatomycosis

Stigmatomycosis is a plant disease caused by the yeast-like fungus Nematospora coryli. This pathogen is a major concern in orchards, particularly due to its unique transmission mechanism. Unlike many other fungal infections that spread through air or water, this disease is primarily vectored by sucking insects, such as true bugs (pentatomids), which introduce the fungus into the fruits during their feeding process.

The disease primarily affects pistachio trees, significantly impacting both yield and quality. Besides pistachios, the pathogen has a wide host range, including various nut, fruit, and legume crops. The presence of the fungus in an orchard is often linked to the presence of its insect vectors, which act as the primary means of long-distance dispersal and successful inoculation of the fruit tissue.

The symptoms of stigmatomycosis are distinct, especially inside the fruit. Infected kernels often exhibit necrotic spots, discoloration, and a bitter, unpleasant taste. In the case of pistachios, the kernel may appear shriveled or display a powdery appearance inside the shell. Since the damage occurs internally, the fruit may look healthy from the outside until it is opened, making it a challenging disease to detect early.

Environmental conditions that favor both the insect vectors and the fungus play a critical role in disease propagation. High humidity and moderate temperatures often correlate with increased insect activity, which in turn leads to a higher incidence of stigmatomycosis. The fungus thrives in the nutrient-rich environment of the developing kernel, rapidly colonizing the tissue once introduced by the insect's piercing-sucking mouthparts.

• Rigorous insect control programs, specifically targeting true bugs during the fruit-set stage.
• Implementation of integrated pest management (IPM) to reduce vector populations.
• Sanitation practices, including the removal of infested fruits and debris.
• Monitoring of orchard health to detect and treat early signs of infestation.

The economic impact of stigmatomycosis is significant, as it leads to high post-harvest losses and reduced marketability of the crop. Because the infection ruins the quality of the kernels, affected batches often fail to meet quality standards. Effective control requires a combination of chemical management of insect vectors and cultural practices designed to maintain orchard hygiene throughout the growing season.