Marasmiellus sheath and shoot rot

Initial symptoms are characterized by browning and decay of the leaf sheaths that tightly wrap the lower parts of the sugarcane stalk. These tissues lose their firmness and begin to rot.

A diagnostic feature of the disease is the presence of white, felt-like mycelium growing on the surface of the infected leaf sheaths. In humid weather, this fungal growth becomes particularly prominent.

As the disease progresses, the infection penetrates the stalk tissues. The stalk becomes discolored, softened, and structurally weakened, which often leads to the lodging of the plants.

Cross-sections of infected stalks reveal necrotic internal tissues. Occasionally, tiny, white, mushroom-like fruiting bodies of the fungus may appear on the surface of the decayed plant parts.

Visually, affected sugarcane stands show signs of stunted growth, premature yellowing of the leaves, and an overall lack of vigor compared to healthy fields.

The causative agent of this disease is the fungus Marasmiellus stenophyllus (formerly classified as Marasmiellus sacchari). It is a basidiomycete fungus that specifically targets the leaf sheaths and stalks of sugarcane plants.

The pathogen is known for its ability to persist in crop debris and soil for extended periods. It spreads through the release of basidiospores that are dispersed by wind or splashing water during heavy rainfall.

Fungal hyphae enter the plant host through natural openings or mechanical wounds. Once inside, the fungus spreads rapidly through the tissue, utilizing specialized enzymes to degrade plant cells.

Marasmiellus stenophyllus is a facultative parasite, meaning it can survive on organic matter while waiting for suitable conditions to attack a living host plant.

The biology of this fungus is highly adapted to humid tropical environments, where moisture levels remain consistently high enough to support its development throughout the growing season.

The development of the disease is heavily dependent on high atmospheric humidity. Prolonged rainy seasons or areas with excessive dew provide the perfect moisture levels for fungal proliferation.

Dense planting patterns are a major risk factor, as they restrict airflow within the canopy and maintain high humidity, creating a microclimate that is ideal for the fungus.

Temperature plays a crucial role, with the range of 25°C to 30°C being optimal for the rapid growth of the fungal colony and subsequent spread of the disease.

Mechanical damage caused by farm equipment or insect pests creates infection courts that allow the fungus to enter the plant tissues more easily.

Poor soil drainage can lead to waterlogging, which weakens the root system and plant health, making the crop significantly more susceptible to Marasmiellus infection.

The primary damage caused by sheath and shoot rot is a significant reduction in overall biomass and harvest yield, as infected plants may die prematurely or collapse.

The fungus negatively impacts the quality of the cane juice by triggering sugar inversion and decreasing sucrose content, which complicates industrial processing and reduces profitability.

Lodging and the weakening of stalks make mechanized harvesting difficult and inefficient, often leading to large quantities of cane being left in the field.

Long-term harm includes reduced stool regeneration in ratoon crops. Plants weakened by the rot show poor regrowth, requiring farmers to replant fields sooner than expected.

In cases of severe infestation, the disease can spread across large plantation areas, leading to significant economic losses and increased expenditure on disease management programs.

Selecting and planting resistant sugarcane varieties is considered the most sustainable and effective method for managing Marasmiellus rot in commercial agriculture.

Implementing proper spacing between rows helps improve air circulation and sunlight penetration, which helps lower the humidity around the stalks and limits fungal growth.

Sanitation practices, such as the removal and destruction of crop residues after harvesting, are essential to reduce the inoculum level and break the disease cycle.

Improving field drainage is critical to prevent water stagnation, which directly helps in controlling the moisture-dependent conditions required by the fungus.

Providing adequate nutrient management, especially balanced potassium levels, helps strengthen plant cell walls, providing a natural defense against fungal invasion.