Glomerella tucumanensis

Glomerella tucumanensis (anamorph: Colletotrichum falcatum) is an Ascomycete fungus and a significant pathogen affecting sugarcane crops globally. It belongs to the genus Colletotrichum, well-known for causing anthracnose-type diseases.

The life cycle involves both sexual and asexual phases. The asexual stage, characterized by conidia formation, is primarily responsible for the rapid spread of the disease within agricultural fields during the growing season.

The fungus is highly adaptable and can survive in crop debris and soil for extended periods. It primarily enters the host plant through wounds, insect-damaged areas, or the root system, where it establishes its mycelium.

Once inside, the fungus colonizes the vascular bundles of the sugarcane stalk. It spreads systemically, disrupting the transport of water and nutrients, which ultimately leads to the collapse of the plant's health.

Effective identification in the field requires close monitoring of crop health, especially in areas with high humidity and warm temperatures, which favor the proliferation and dissemination of fungal spores.

The primary damage caused by Glomerella tucumanensis is known as 'red rot of sugarcane'. This disease is economically devastating as it directly affects both the biomass and the sugar quality of the crop.

The fungus produces enzymes that invert sucrose, converting it into glucose and fructose, which are then consumed by the fungus. This process drastically reduces the yield of extractable sugar in processed stalks.

Infected stalks become brittle and susceptible to lodging (breaking). Lodged crops are extremely difficult to harvest mechanically, resulting in further yield losses and higher production costs for farmers.

The disease can also cause stalk rot in stored seeds, severely affecting the germination rates in subsequent seasons. Using infected planting material is a primary driver of disease spread in new fields.

Widespread infections can lead to the total loss of a plantation if environmental conditions remain conducive to the fungus, leading to a massive decrease in overall sugarcane production.

The most diagnostic sign is found by splitting a sugarcane stalk longitudinally. Affected internal tissues show reddish discoloration intermingled with white horizontal spots, characteristic of red rot.

External symptoms often manifest as the yellowing and wilting of leaves starting from the apex. As the disease progresses, the entire plant turns brown and eventually dries out as the internal vascular tissue is destroyed.

In humid conditions, small, dark fruiting bodies (acervuli) may emerge on the stalk's surface. These structures release masses of conidia that can be spread by rain splashes and wind to surrounding plants.

Fields affected by red rot often show irregular patches of stunted plants. These patches stand out against the healthy portion of the crop due to the visibly weakened and necrotic state of the foliage.

A sour, alcoholic odor is often emitted from the inside of infected stalks. This smell is a byproduct of the fungal metabolism acting on the sugars within the sugarcane tissues.

The most sustainable strategy for managing Glomerella tucumanensis is the cultivation of resistant sugarcane varieties. Breeding programs focused on resistance are the primary line of defense.

Strict phytosanitary practices are essential, including the use of pathogen-free seed canes. Heat treatment (hot water soak) of setts before planting is a common practice to eliminate dormant fungal structures.

Integrated pest management (IPM) to control stem-boring insects is crucial. By preventing insect damage, growers limit the number of entry points available for the fungus to penetrate the stalks.

Crop rotation and effective field sanitation, such as removing and burning infected crop residues, are necessary to reduce the inoculum level of the pathogen in the soil for future plantings.

Managing soil moisture and avoiding excessive irrigation can create a less favorable environment for the pathogen, helping to inhibit the spread of spores during critical growth stages.