Phoma blight of pigeon pea

The disease known as Phoma blight is caused by the fungus Phoma cajani, which is a significant pathogen of pigeon pea (Cajanus cajan). This fungal infection is classified among the Deuteromycetes and presents a major threat to agricultural productivity in tropical regions where pigeon pea serves as a primary source of protein and soil fertility.

The host range is primarily limited to species within the Cajanus genus. Phoma cajani is highly effective at exploiting these hosts at different growth stages, particularly targeting foliage, stems, and pod tissue. The fungus survives primarily on infected crop debris left in the field, making it a persistent threat that can lead to significant yield losses if not properly managed.

Symptoms of the infection manifest as necrotic lesions that appear on leaves and stems. These lesions are typically brown or black, often circular or irregular in shape, containing visible black pycnidia (fruiting bodies) within the lesion center. As the fungus colonizes the stem, it can cause stem breakage and wilting, which disrupts nutrient transport and compromises the integrity of the plant.

Environmental conditions play a crucial role in the development and spread of Phoma cajani. High humidity, cloud cover, and moderate temperatures create an ideal environment for spore germination. Rainfall is a major vector, as splashing water carries spores from infected plant litter onto healthy tissue, facilitating rapid secondary spread within the canopy during the growing season.

Management strategies focus on reducing the initial inoculum load in the field. Essential practices include the implementation of a strict 3-year crop rotation, deep plowing to bury infested plant remains, and the use of resistant cultivars when available. Fungicidal applications are effective for disease suppression; growers should utilize systemic fungicides as a preventative measure if climatic conditions indicate high risk for infection.