Ramulispora sorghicola

Ramulispora sorghicola is a fungal pathogen responsible for the disease known as zonate leaf spot of sorghum. Taxonomically, it is classified within the Ascomycota phylum. This pathogen specifically targets plants of the Sorghum genus, causing significant damage to grain sorghum, forage sorghum, and sudangrass worldwide, particularly in warm and humid climates.

The disease is characterized by the formation of distinct, circular to elliptical spots on the leaves. These lesions often display a zonate appearance, with alternating bands of light and dark necrotic tissue. In advanced stages, the centers of these spots may contain minute, black fungal fruiting bodies known as acervuli. Under severe infection pressure, premature leaf senescence occurs, which significantly reduces the photosynthetic capacity of the sorghum plant.

The life cycle of the pathogen is driven by its ability to overwinter on infected crop residues left on the soil surface. Ramulispora sorghicola survives the dormant season as mycelium or micro-sclerotia within decaying plant tissues. With the onset of favorable conditions in the spring, primary inoculum is produced, which is then disseminated to healthy leaves via water splashes and air currents during rainfall.

Environmental conditions are the primary drivers of disease outbreaks. The fungus thrives in warm temperatures ranging from 20°C to 28°C accompanied by high humidity. Frequent rainfall and prolonged periods of leaf wetness facilitate the germination of conidia and the subsequent penetration of the host tissue. Such conditions are conducive to rapid secondary cycles of infection, allowing the disease to spread across the field quickly.

The economic impact of this pathogen is reflected in reduced grain yields and poor quality of forage. Management practices focus on reducing the primary inoculum source and protecting the crop during vulnerable growth stages. Key control strategies include:

• Planting resistant or tolerant sorghum hybrids.
• Implementing crop rotation with non-host species to interrupt the life cycle.
• Deep tillage to bury crop debris and accelerate decomposition.
• Timely application of systemic fungicides if conditions for disease development persist.