Cotton virescence

Cotton virescence is a severe plant disease caused by phytoplasmas, which are specialized wall-less bacteria that inhabit the plant's phloem tissue. These pathogens disrupt the movement of essential nutrients and hormones within the plant, leading to systemic physiological collapse. It is considered a significant threat in several cotton-growing regions globally.

The primary host for this disease is the cotton plant (Gossypium spp.), but the phytoplasmas responsible for virescence have a broader host range. Many weed species, particularly those in the Malvaceae family, serve as asymptomatic reservoirs for the pathogen. These weeds allow the phytoplasma to persist throughout the year, even in the absence of the cotton crop.

The characteristic symptoms of the disease include the greening of flower petals (virescence) and the development of abnormal, leafy structures instead of floral organs (phyllody). Affected plants often exhibit stunted growth, excessive proliferation of axillary shoots leading to a bushy appearance, chlorosis of leaves, and small, malformed bolls that result in poor quality lint.

The dissemination of the pathogen is entirely dependent on insect vectors, primarily leafhoppers. These insects acquire the phytoplasma by feeding on infected phloem and subsequently transmit it to healthy plants. Environmental conditions such as warm, dry weather are particularly favorable for the migration and breeding of these vectors, which accelerates the spread of the disease.

Management of cotton virescence is challenging due to the systemic nature of the pathogen and the difficulty in controlling mobile insect vectors. An effective integrated pest management (IPM) strategy should prioritize:

• Elimination of alternative weed hosts in and around cotton fields;
• Monitoring and management of leafhopper populations using targeted insecticides;
• Use of certified, disease-free planting material;
• Implementation of crop rotation and spatial isolation of new cotton fields from heavily infected areas.