Anthracnose caused by Colletotrichum queenslandicum

Initial signs appear as small, sunken, circular or oval spots on leaves, stems, and fruits. Over time, the color of the affected areas changes from light brown to dark brown, sometimes with a distinct dark margin.

Under high humidity, characteristic pads form on the surface of the spots, consisting of accumulations of fungal conidia. These may have a pink, orange, or cream tint, which is a diagnostic feature of the Colletotrichum genus.

Stem infections cause ulcers that can encircle the plant, leading to wilting and death of parts located above the infection site. Tissues often crack in these areas, disrupting normal sap flow.

Fruits affected by this type of anthracnose develop water-soaked spots that rapidly increase in size. Deep infection results in tissue rotting, making the harvest completely unsuitable for sale or storage.

The overall health of the plant deteriorates significantly: premature leaf drop, shoot deformation, and substantial growth retardation are observed, which negatively impacts crop productivity.

The disease is caused by an imperfect fungus of the genus Colletotrichum, known as Colletotrichum queenslandicum. This pathogen belongs to the Ascomycota phylum and specializes in infecting a wide range of agricultural crops, primarily in tropical and subtropical regions.

The fungus persists in plant debris, soil, and seed material as mycelium or conidia. A crucial aspect of the pathogen's life cycle is its ability to engage in saprotrophic nutrition, which allows it to survive in the environment for extended periods until a susceptible host appears.

Conidia are spread mainly through rain splashes, irrigation water, wind, and by moving contaminated planting material. The infection penetrates through the plant epidermis, often utilizing natural openings or mechanical tissue injuries.

The microscopic structure of the fungus is characterized by the formation of acervuli, within which numerous single-celled, colorless conidia mature. These structures ensure massive infection of new areas throughout a single growing season.

A biological feature of C. queenslandicum is its aggressiveness under high temperature and humidity conditions. The pathogen adapts rapidly to changing environmental factors, creating hidden infection hotspots within crops.

Optimal conditions for infection development involve a combination of temperatures from +22 to +28 degrees Celsius and relative air humidity above 85 percent. Such indicators are critical for spore germination.

Frequent precipitation, fog, and heavy dew in the morning create a favorable environment for intense sporulation. Moisture droplets on leaf surfaces are essential for conidia to germinate and penetrate the host plant tissues.

Poor aeration in crops, caused by dense planting, significantly increases the risk of epiphytotics. Stagnant air in the lower part of the plants contributes to prolonged moisture retention, which provokes accelerated pathogen development.

Breaches of agrotechnical rules, particularly excessive nitrogen fertilization, reduce the plant's natural resistance. Excessively tender, overfed tissues are more easily attacked by fungal hyphae.

The presence of weeds in the field often serves as an additional risk factor, as many weeds can act as reservoirs for Colletotrichum queenslandicum during periods when the main crop is not present.

The harm caused by the disease manifests in direct crop losses, which can reach 50–70 percent without protective measures. The pathogen infects both vegetative and reproductive organs, preventing the plant from forming healthy fruits.

Damaged fruits lose their commercial quality and flavor, and are prone to secondary bacterial rot during storage. This leads to significant economic losses during both the cultivation and logistics stages.

Contaminated seeds and seedlings become a source of disease spread to new territories. Using poor-quality planting material leads to reduced germination and weak plant development from the earliest stages of ontogenesis.

The disease weakens the plant, making it vulnerable to adverse environmental factors. Due to the massive death of photosynthetic surfaces, the plant's metabolic processes are suppressed, leading to nutrient deficiencies.

Long-term survival of the fungus in soil and debris complicates crop rotation. This necessitates the implementation of expensive field cleaning measures and long gaps in cultivating susceptible crops on specific land.

The foundation of control is the use of healthy, certified seed material. Before sowing, seeds should be treated with fungicides or subjected to thermal disinfection to eliminate spores.

Adherence to crop rotation rules is a key preventive stage. It is not recommended to return susceptible crops to the same location for at least 3–4 years. Grain crops make the best preceding plants.

Agrotechnical measures should be aimed at creating conditions unfavorable for the pathogen: regular weeding, timely removal and destruction of infected plant debris, and proper root-zone watering.

The use of chemical crop protection products is justified during periods of high threat. Effective products include those based on copper, strobilurins, and systemic triazole fungicides that block mycelial development.

• Timely diagnosis of the disease at early stages.
• Organizing crop ventilation to reduce humidity.
• Use of varieties showing resistance to anthracnose.
• Regular monitoring of plant health status.
• Implementation of preventive sprays before the flowering period.