Cotton leaf spot

The fungus Mycosphaerella gossypina (anamorph: Cercospora gossypina) is the causative agent of a widespread fungal disease known as cotton leaf spot. It is a major pathogen of the cotton plant, affecting crop vitality and yield potential in various tropical and subtropical regions where humidity is consistently high.

The primary host for this pathogen is the cotton plant (Gossypium hirsutum and other species). The infection can manifest on various parts of the plant, including leaves, stems, and bolls. When conditions are favourable for the pathogen, it can cause severe defoliation, particularly in the lower canopy of the plant, before moving upward during the later stages of the growing season.

Symptoms typically begin as small, irregular or circular spots on the leaf blades. As the lesion matures, the center turns grey or light brown, often surrounded by a dark brown or purple halo. Under high humidity, the fungal growth (conidiophores and conidia) becomes visible on the underside of the leaves. Severe infection causes leaves to turn chlorotic, curl, and wither prematurely.

The development of the disease is heavily dependent on moisture. High relative humidity and warm temperatures (ranging from 25°C to 30°C) are critical for spore germination and infection. The pathogen overwinters as mycelia or perithecia in infested cotton debris remaining in the soil from the previous season. Rain splashes and wind are the primary vectors for dispersing spores to healthy plants.

The economic impact of this disease is significant, as it leads to premature leaf drop, which reduces the plant's photosynthetic capacity. This negatively affects the accumulation of biomass and the development of cotton bolls, ultimately decreasing both yield and fiber quality. Effective control strategies include:

• Deep plowing to bury crop residues and reduce primary inoculum.
• Implementation of crop rotation to break the pathogen's life cycle.
• Use of certified, pathogen-free seeds.
• Timely application of appropriate fungicides during the onset of the disease.