Bipolaris leaf spot of cotton

Bipolaris leaf spot is a fungal disease affecting cotton plants caused by the pathogen Bipolaris gossypina. This fungus belongs to the family Pleosporaceae and is recognized as a significant constraint to cotton production in tropical and subtropical regions where environmental conditions favor its development.

The primary host for this pathogen is the cotton plant (Gossypium species). The disease affects various plant parts including cotyledons, true leaves, stems, and especially the bolls. It can occur throughout the growing season, posing a risk from the seedling stage up to boll maturation.

The characteristic symptoms begin as small, reddish-brown spots on the leaves. As the infection progresses, these lesions enlarge and often develop a darker, necrotic center with a purplish or yellow halo. Under humid conditions, a dark, velvety layer of conidiophores and spores develops over the lesions, facilitating rapid spread to neighboring leaves.

The development of Bipolaris gossypina is highly dependent on environmental factors, particularly moisture. High relative humidity and warm temperatures significantly promote spore germination and fungal mycelial growth. The pathogen survives in crop debris and contaminated seeds, which serve as the primary inoculum for subsequent cropping seasons.

Economic damage is caused by the defoliation of plants, which reduces the photosynthetic area and leads to stunted plant growth. Furthermore, infection of the cotton bolls results in lower fiber quality and reduced seed oil content. Effective management involves the use of certified healthy seeds, deep plowing to bury infected residues, and the application of fungicides during periods of high disease pressure.