Yellow spot of sugarcane

Yellow spot of sugarcane is caused by the fungus Mycovellosiella koepkei, formerly classified as Cercospora koepkei. This pathogen belongs to the Deuteromycota division.

The fungus is characterized by the production of slender conidiophores that emerge in clusters through the stomata of the host plant leaves.

The pathogen is highly host-specific, primarily affecting sugarcane (Saccharum officinarum) and closely related species within the Saccharum genus.

Microscopic identification reveals pale olive-colored conidia that are adapted for wind and water-splash dispersal in humid tropical environments.

The fungus survives between cropping seasons on infected crop residues, which serves as the primary inoculum for subsequent sugarcane plantings.

The disease primarily attacks the leaf blades of sugarcane, which are essential for photosynthesis and sugar synthesis during the plant's development.

By reducing the functional leaf area, the fungus significantly restricts the plant's ability to store sucrose, leading to lower yields at harvest time.

Severe outbreaks in susceptible cultivars can result in substantial losses, as the premature death of leaves limits the plant's overall vigor and growth rate.

In addition to yield loss, the disease can impact the quality of the cane juice by altering the metabolic processes within the plant tissues.

Younger, actively growing cane is particularly vulnerable, and persistent infections can lead to stunted growth and reduced biomass production.

The development of yellow spot is heavily dependent on warm, humid conditions with frequent rainfall, typical of the tropical sugarcane production belt.

Optimal temperatures for the germination and spread of M. koepkei range between 22°C and 28°C, often coinciding with the wet season.

Dew and high atmospheric humidity on leaf surfaces are critical for the initial infection process, as they facilitate the germination of fungal spores.

Disease incidence usually increases gradually throughout the growing season, reaching its peak when the canopy is dense and airflow is restricted.

In drier periods, the disease progression slows down, but the pathogen persists in a latent or dormant state until favorable humidity levels return.

The initial symptoms are small, yellow, chlorotic spots that appear on the leaves, often arranged in a somewhat linear fashion along the veins.

As the infection advances, these spots expand, turn brown or reddish-brown, and may develop a distinct yellow halo around the necrotic center.

• Development of diffuse yellow spots on the leaf blade.
• Enlargement and transition of spots into brown necrotic areas.
• Visible greyish-olive mold growth on the underside of leaves.
• Curling and wilting of leaf tips in heavily infected plants.
• Premature yellowing and senescence of the lower foliage.

Under humid conditions, the underside of the leaves may be covered with a dense mat of spores, which provides a tell-tale sign of the pathogen's presence.

The most effective strategy for managing yellow spot is the cultivation of resistant or tolerant sugarcane varieties, which minimizes the need for intervention.

Field sanitation, including the removal or burning of infected sugarcane trash after harvest, significantly reduces the amount of initial inoculum.

Promoting good agricultural practices, such as appropriate planting density, helps to improve airflow within the canopy and reduces leaf surface moisture.

Fungicide applications, while not always economically viable for commercial sugar production, can be used in nurseries or high-value seed multiplication areas.

Balanced crop nutrition, specifically avoiding nitrogen excess and ensuring adequate potassium, can help enhance the plant's natural resistance to fungal pathogens.