Cotton anthracnose

Classified as a hemibiotrophic pathogen, it initially colonizes living plant tissues before shifting to necrotrophic behavior, which leads to tissue collapse and the formation of characteristic lesions.

The fungus produces large quantities of conidia in acervuli, which serve as the primary inoculum for spreading the disease within the field during favorable weather conditions.

It is capable of overwintering as mycelium or dormant spores within contaminated cotton seeds, as well as in crop debris left in the soil after harvest.

The pathogen demonstrates a high level of specialization, with distinct strains varying in their aggressiveness towards different cotton varieties and environmental adaptations.

Early symptoms appear on seedlings as small, water-soaked, reddish-brown spots on the cotyledons. As the infection progresses, these lesions extend to the hypocotyl, causing stem girdling and seedling damping-off.

On older plants, the foliage may exhibit irregular, necrotic lesions that gradually expand. Severe infection leads to premature leaf senescence and defoliation, significantly reducing the photosynthetic capacity of the plant.

The most distinctive signs occur on the bolls, where sunken, dark brown to black spots develop. In humid conditions, these spots are covered with a characteristic pinkish or salmon-colored spore mass.

Internal boll damage results in stained, brittle fiber. If the infection reaches the seed inside, it becomes shriveled and carries the pathogen into the next season.

• Stunting of terminal buds.
• Stem necrosis and cankers.
• Discolored and low-quality lint fibers.
• Premature boll opening or failure to open.
• Massive premature shedding of squares and bolls.

The development of cotton anthracnose is highly dependent on high relative humidity and frequent rainfall. Prolonged dew periods or irrigation patterns that keep foliage wet significantly promote spore germination.

The optimal temperature range for the pathogen's growth and infection processes is between +20°C and +28°C. Deviations from these temperatures may slow down the disease cycle but do not eliminate the risk.

Dense crop canopy and poor air circulation create a localized microclimate that fosters the rapid spread of conidia from infected plants to neighboring healthy ones.

Excessive nitrogen fertilization can lead to lush, succulent growth that is more susceptible to penetration by the fungal mycelium.

Wounds caused by insects such as the cotton bollworm or mechanical damage from field equipment act as entry points for the pathogen, accelerating the infection process significantly.

The primary economic impact of this disease is the reduction in plant stand density due to seedling blight, which often necessitates costly replanting operations.

Infection of the bolls leads to significant quantitative and qualitative losses in lint production. The damaged fibers lose their physical strength and aesthetic quality, making them difficult to process.

Yield reduction also occurs due to the premature shedding of fruiting structures, which prevents the plant from reaching its full potential in terms of boll count per plant.

Seed transmission poses a major long-term risk, as infected seeds effectively distribute the pathogen to previously clean fields, complicating disease management efforts.

Farmers face increased production costs due to the need for fungicide applications and intensified monitoring of the crop throughout the entire growing season.

The use of high-quality, certified, and fungicide-treated seeds is the most effective preventative measure against the primary introduction of the disease.

Implementing a robust crop rotation strategy is essential. Rotating cotton with non-host crops for at least 3 years helps deplete the pathogen population within the soil.

Post-harvest management involves the immediate incorporation or destruction of cotton residues. This practice minimizes the survival of the fungus in the soil and reduces the initial inoculum for the following year.

Foliar application of systemic fungicides during the early boll development stage can suppress secondary infection cycles, especially in regions with frequent summer rainfall.

Integrated pest management (IPM) to control insects that wound cotton bolls is critical for preventing the entry of Colletotrichum indicum and limiting the spread of the disease.