Sorghum anthracnose

Symptoms typically begin as small, water-soaked lesions on the leaves, which gradually expand and develop characteristic reddish, purple, or tan necrotic centers.

Leaf lesions are often elliptical or spindle-shaped, surrounded by a distinct lighter-colored halo, and eventually become covered in black, hair-like setae.

Stalk infection manifests as internal rot, which weakens the plant stem, compromises nutrient transport, and leads to premature lodging and head death.

Head infection can cause grain abortion or shriveling, significantly reducing both the quality and quantity of the harvestable yield.

Under humid conditions, a pinkish or grey fungal mass of spores may be visible on the lesion surfaces, which is a diagnostic indicator of active anthracnose.

The causal agent of sorghum anthracnose is the pathogenic fungus Colletotrichum lineola (formerly known as Colletotrichum graminicola). It is a destructive fungus affecting all parts of the sorghum plant throughout its growth cycle.

The fungus survives on infected crop residues in the soil and can also be seed-borne, making sanitation and quality seed selection critical for initial disease management.

Disease transmission occurs via conidia, which are easily disseminated by wind, rain splashes, and farm equipment during field operations.

The pathogen infects plants by penetrating epidermal cells or natural openings, subsequently colonizing the intercellular space to absorb nutrients from the host.

As the infection matures, the fungus develops acervuli, which are specialized structures producing large amounts of spores, ensuring the rapid spread of the disease during the season.

Anthracnose thrives in warm and humid environments, with optimal infection occurring at temperatures between 22°C and 28°C and high relative humidity.

Frequent rainfall and persistent morning dew create the necessary surface moisture for conidial germination and host tissue invasion.

Dense crop stands reduce air movement, leading to a microclimate within the canopy that favors rapid fungal proliferation and secondary infections.

Continuous cropping of sorghum on the same land allows for the accumulation of the pathogen's inoculum in the soil, significantly increasing infection pressure.

Stressed plants, whether due to nutrient imbalances or other pest damage, are markedly more susceptible to successful colonization by the fungus.

Sorghum anthracnose is recognized as one of the most significant yield-limiting diseases, capable of causing devastating crop losses in conducive seasons.

Severe defoliation drastically reduces the plant's photosynthetic capacity, which directly results in poor seed filling and lower overall biomass production.

Stalk rot often leads to plant collapse (lodging), making mechanical harvesting extremely difficult and resulting in significant grain loss in the field.

Infected seeds often exhibit reduced germination rates and weakened seedling vigor, which can lead to poor stand establishment in the following season.

The overall economic impact includes not only direct yield loss but also increased production costs associated with intensive chemical control measures.

The most reliable and cost-effective method of managing sorghum anthracnose is the deployment of genetic resistance through resistant hybrids and varieties.

Implementing a diverse crop rotation is essential to break the survival cycle of the pathogen by depriving it of its specific host for several years.

Proper field sanitation, including the deep burial or destruction of infested crop debris, significantly lowers the primary inoculum level for the next season.

Seed treatment with broad-spectrum systemic fungicides is a crucial proactive measure to protect the crop during the vulnerable seedling emergence stage.

• Application of foliar fungicides at the onset of symptoms during the growing season.
• Managing plant density to promote better air circulation and leaf drying.
• Implementing integrated weed management to remove potential alternative hosts.
• Ensuring balanced fertilization to promote plant health and cell wall integrity.