Passalora leaf spot of pepper

Passalora leaf spot, caused by the fungus Passalora capsicicola, is a significant plant disease affecting pepper crops worldwide. As a specialized pathogen belonging to the kingdom Fungi, it primarily targets the foliage of Capsicum species, leading to severe defoliation if left unchecked in favourable environmental conditions.

The symptoms of the disease typically appear on the leaves as small, circular or irregular necrotic spots. These spots initially appear brown, but as they expand, they develop a lighter greyish-white center often surrounded by a darker margin. Under conditions of high humidity, the undersides of the leaves show a characteristic velvety growth, which consists of the fungus's conidiophores and conidia.

The biology of Passalora capsicicola is heavily reliant on survival through the off-season. The pathogen overwintering occurs primarily on infected plant debris left in the soil or on contaminated seeds. When warm, moist conditions return in the following season, the spores (conidia) are dispersed by wind, splashing rain, or overhead irrigation, landing on healthy plant tissue to initiate the infection cycle.

Disease development is highly favored by moderate to warm temperatures ranging from 20 °C to 28 °C, combined with prolonged leaf wetness or high relative humidity. Greenhouse environments with poor ventilation or densely planted fields provide an optimal microclimate for the fungus to multiply rapidly, causing secondary infections throughout the growing season.

The economic impact of this pathogen is reflected in the loss of photosynthetic leaf area, which severely impairs fruit development and reduces the overall yield. Controlling Passalora capsicicola requires an integrated pest management (IPM) approach. Essential strategies include implementing strict crop rotation, removing and destroying infested plant material, optimizing plant spacing to improve airflow, and applying protective fungicides during the early stages of disease pressure.