Tropical rust of maize

The causal agent of tropical rust of maize is the fungal pathogen Physopella zeae (also known as Angiopsora zeae). This fungus is an obligate parasite that specifically affects maize crops, primarily in tropical and subtropical agro-climatic zones. The disease is known for its ability to cause rapid damage during the active growing season of the host plant.

Maize (Zea mays) is the main host for this pathogen. While it primarily targets corn, the pathogen's ability to produce massive amounts of urediniospores allows it to spread rapidly across large landscapes. These spores can be carried by wind over long distances, making it a challenging disease to contain once it is introduced into a new region.

The visual symptoms appear as small, circular or elliptical pustules located on both surfaces of the leaves. Initially, these pustules are light or yellowish in color, reflecting the early stages of spore production. As the infection progresses, they turn brown or dark reddish-brown, often causing the leaves to dry out prematurely and potentially affecting the overall plant vitality.

Environmental conditions play a crucial role in the disease cycle of Physopella zeae. High relative humidity (frequently above 80%) and warm temperatures ranging from 20°C to 28°C are optimal for spore germination and colonization. Frequent rainfall, dew, and foggy weather significantly increase the probability of an epidemic, as they facilitate the spread and infection processes.

The economic impact of tropical rust is significant, as it leads to reduced leaf area index, impaired photosynthesis, and consequently lower yields. Effective management requires a multifaceted approach:

• Deployment of disease-resistant corn hybrids.
• Crop rotation to reduce the inoculum levels in the soil.
• Fungicide applications to control outbreaks in high-risk areas.
• Field sanitation, including the destruction of crop residues where the fungus can survive.