Passalora leaf spot of astragalus

Passalora astragali is a fungal pathogen responsible for leaf spot disease in various species of Astragalus. This disease is a significant concern in agricultural settings, particularly where astragalus is cultivated for pharmaceutical use or forage purposes, as it directly impacts plant health and biomass quality.

The fungus primarily targets the foliage of the host plants. While the leaves are the most commonly affected tissues, severe infections may extend to petioles and stems. The premature loss of leaf tissue significantly reduces the photosynthetic capacity of the plant, leading to stunted growth and reduced vigor.

Typical symptoms include the appearance of distinct lesions on the leaves. These spots are usually brown to dark brown and may vary in size and shape. A key diagnostic feature is the presence of an olive-brown, velvety-looking fungal growth on the underside of the leaves, which consists of conidiophores and conidia produced by the pathogen.

Environmental conditions play a crucial role in the development and spread of Passalora astragali. The fungus thrives in warm, humid weather. Spores are primarily disseminated by wind currents and water splashes from rain or overhead irrigation. Overwintering occurs in crop residues or the soil, making field sanitation a critical factor in disease management.

Effective management requires an integrated approach to disease prevention. Key practices include:

• rotation of crops to break the disease cycle;
• sanitation measures such as removing and destroying infected plant debris;
• application of appropriate fungicides if the infection pressure is high.