Sorghum rust is a fungal disease of sorghum and other grass species. This disease is one of the most serious diseases of sorghum and can cause significant yield losses. It is an economically important disease in many parts of the world, especially in subtropical and tropical regions.
Sorghum producers must understand the disease cycle, its environmental interaction, and risk factors to prevent and manage this disease. Control measures for sorghum rust include good crop management practices, using resistant cultivars, and applying fungicides. This article will provide an overview of sorghum rust disease, including its symptoms, biology, and control.
Rust Disease Management in Sorghum
The Causal Organism of Sorghum Rust Disease
- Puccinia purpurea, a member of the family Pucciniaceae, an obligate parasite, has a wide host range, which means it can infect many different sorghum species.
- The uredospores are deep brown, pedicellate, ellipse, or ovoid, with thin walls and spiny edges.
- The teliospores are bi-cellular, spherical at the peak, and range between red to brown. Every cell consists of one germ pore. Teliospores grow into promycelium and basidiospores on germination.
- The alternative host, Oxalis corniculata, is infected by basidiospores, on which pycnial and aecial phases develop.
The Disease Cycle of Sorghum Rust Disease
- Uredinia, small, raised, reddish-brown pustules on plant leaves, start the cycle. Uredinia have haploid urediniospores and diploid teliospores.
- These spores can survive for months or years, enabling the fungus to overwinter and stay dormant until the next growing season.
- Telia, bigger, darker pustules on an infected plant stem, form in the second stage.
- Telia has two teliospores. These spores survive longer than urediniospores.
- Teliospores germinate, and basidia, spore-producing structures on the telia’s upper surface, form in the third stage.
- Haptloid basidiospores from basidia invade healthy plants.
Mode of spread and survival of the pathogen in sorghum crop
- Insects, wind, or rain spread fungal spores, infecting crops anytime.
- Uredospores remain inert in soil and plant residues for longer.
- Oxalis corniculata, an alternate host, helps perpetuate the fungus.
Causes / Conditions Favorable for Sorghum Rust Disease Spread in the field.
- Rainfall – The rainy weather condition facilitates the disease incidence.
- Temperature – Cooler temperatures of 10-12 °C facilitate teliospores’ germination.
Symptoms of Sorghum Rust Disease
- Sorghum Rust Disease causes severe defoliation, reduced grain quality, and yield losses.
- The disease is characterized by yellow-orange pustules or spots on the leaves, stems, and other parts of the plant, which can turn brown and eventually become powdery.
- The presence of small flecks on lower leaves and reddish powdery masses of uredospores. The pustules or spots may also be present on the leaf sheaths and the stalks of inflorescence.
- The leaves may also become distorted, and the grains may be affected. In severe cases, the plant may die completely.
Percentage of yield loss due to Sorghum Rust Disease in Sorghum crop
- The yield losses caused by sorghum rust can be significant. The percentage of yield loss due to the disease can range from 5-30%.
- Yield losses may be higher in areas with more severe diseases, such as in certain parts of Africa and India.