Common rust of corn

Puccinia sorghi is an obligate biotrophic fungus within the kingdom Fungi, phylum Basidiomycota, and order Pucciniales. It is the primary causal agent of common rust in maize (corn), a disease that significantly impacts crop productivity worldwide by targeting the foliage of the plants.

The pathogen is identified by the formation of small, oval, powdery pustules known as uredinia. These pustules typically appear on both the upper and lower surfaces of corn leaves, releasing reddish-brown spores that can be easily transported by wind to infect other plants within the same field or neighboring areas.

The biological cycle of this pathogen involves an alternation of hosts, with species of Oxalis (wood sorrel) acting as the alternate host for the sexual stage of the fungus. However, the asexual urediniospores are the primary cause of rapid disease spread during the growing season, especially in regions with favorable climatic conditions.

Environmental conditions play a crucial role in the development of Puccinia sorghi. High humidity, heavy dews, and moderate temperatures (ranging from 16°C to 25°C) are optimal for the germination of spores and the progression of the disease. Prolonged periods of overcast weather often lead to severe infection outbreaks.

The economic impact of common rust is manifested in reduced grain filling, lower overall yield, and compromised nutritional quality of the maize. To effectively control the disease, agronomists recommend implementing integrated management strategies, such as planting resistant hybrids, practicing good crop rotation, and applying systemic fungicides if the disease threshold is exceeded.