Alternaria leaf spot of sweet potato

The causative agent of this disease is the fungus Alternaria bataticola, belonging to the group of deuteromycetes. It is a specialized plant pathogen that primarily affects sweet potato (Ipomoea batatas), causing significant damage in humid tropical and temperate regions. The fungus impacts both the foliage and the tubers, reducing the overall vitality and storage quality of the crop.

The disease primarily targets sweet potato plants. The fungus enters the plant tissue through stomata or mechanical wounds. Spore dispersal is facilitated by wind, rain splashes, and movement of contaminated farm equipment. High plant density and poor air circulation within the canopy provide an optimal environment for the germination of fungal conidia and subsequent infection of healthy plant tissues.

The visual symptoms of the infection include the appearance of small, dark, or black spots on the leaves. These lesions often expand and may develop a yellow chlorotic halo around them. As the disease progresses, the central parts of the spots may show a velvety growth of conidiophores. Severe infections result in extensive leaf necrosis, premature senescence, and defoliation, which hampers the plant's ability to produce large, healthy tubers.

Conditions favorable for the development of Alternaria bataticola include periods of high relative humidity, frequent rainfall, and moderate temperatures. The fungus overwinters in infested crop debris left in the field, in the soil, and on infected storage roots. If environmental conditions remain humid, the cycle of infection can repeat rapidly throughout the growing season.

The economic impact of the disease is substantial due to yield loss and potential tuber decay in storage. Integrated management strategies are essential for effective control:

• Practice strict crop rotation to reduce the pathogen population in the soil.
• Use only healthy, disease-free planting material to prevent initial infection.
• Remove and destroy all infected plant debris after harvest to break the infection cycle.
• Apply preventative fungicide sprays (such as copper-based or systemic fungicides) when weather conditions are favorable for disease development.
• Ensure adequate spacing between plants to improve airflow and reduce leaf wetness duration.