Rectangular leaf spot disease is a major fungal disease of sorghum, a cereal crop grown in many areas of the world. The disease infects the leaves, stems, and panicles of sorghum plants. The disease is most severe in warm, humid climates and is typically seen in the United States’ southern states. The disease can spread rapidly within a field and lead to significant sorghum production losses.
To prevent and manage this disease, sorghum producers must understand the disease cycle, its environmental interaction, and risk factors. Cultural practices such as crop rotation, resistant cultivars, and fungicide applications can all be used to manage and reduce the incidence of the disease. This article will provide an overview of sorghum rectangular leaf spot disease, including its symptoms, biology, and control.
Rectangular Leaf Spot Management in Sorghum
The Causal Organism of Sorghum Rectangular Leaf Spot Disease
- Cercospora sorghi, a member of the Ascomycota, an obligate parasite, is a saprophyte living on decaying organic matter.
- The fungus is most commonly found in warm and humid climates, and sorghum grown in these conditions is most susceptible to infection.
- The Mycelium of the fungus is transparent and septate or compartmentalized.
- Conidiophores arise in groups via stomata that are brown-colored and simple in structure, occasionally branched.
- Conidia are transparent, thin-walled, ranging between bi-cellular to multi-cellular, long, and thickened at the distal end.
The Disease Cycle of Sorghum Rectangular Leaf Spot Disease
When the fungus infects sorghum, small, circular, yellow spots at first develop on the leaves. The spots enlarge and multiply as the disease worsens, ultimately fusing to form irregularly shaped, rectangular spots. These spots can be found on both sides of the leaf and range in hue from dark brown to black. A yellow halo may form around the spots as the disease progresses. The fungus can also harm sorghum plant stalks and seeds.
Mode of Spread and Survival of the Pathogen in Sorghum Crop
- The conidia stay viable for up to 5 months. The disease is dispersed through air-borne and seed-borne conidia.
- It is spread by wind, rain, and contact with infected plants, and can survive in the soil for several years. Once the fungus is established in a field, eradicating it cannot be easy.
Causes / Conditions Favorable for Sorghum Rectangular Leaf Spot Disease Spread in the Field.
- High Humidity & Rainfall – The rainy weather and humidity of up to 90% facilitate the disease incidence.
- Temperature – Cooler and more moist weather cond