Anthracnose (Colletotrichum hsienjenchang)

The first symptoms of the infestation appear as small yellowish or brown spots, which over time take on an angular or rounded shape. A characteristic light halo is often noticeable around the spots, indicating the secretion of toxins by the fungus.

In high humidity conditions, pink or salmon-colored pads form on the surface of the spots — the fungal sporulation. In dry weather, these spots may dry out and crack, forming holes in the leaf blade, resembling a "shot-hole" effect.

On stems and petioles, the disease manifests as elongated, sunken dark brown lesions. With severe development of the infection, the lesions girdle the stem, leading to wilting and the subsequent death of the entire vegetative part of the plant above the site of infection.

Fruits are affected most aggressively: deep, weeping lesions covered with a pink coating appear on them. Such damage makes the commercial produce completely unsuitable for sale and storage, as they become entry points for secondary bacterial infections.

The root system is affected less frequently by this species, but the pathogen is capable of causing systemic plant suppression, which manifests as chlorosis and a slowdown in the general growth of the crop.

The causative agent of the disease is the microscopic phytopathogenic fungus Colletotrichum hsienjenchang, which belongs to the class of ascomycetes. This species is highly specialized, primarily affecting members of the Cucurbitaceae family, such as cucumbers, melons, and zucchini.

The fungus survives in infected plant debris in the soil, as well as on seed material in the form of mycelium, sclerotia, or conidia. The infection can overwinter in protected ground on greenhouse structures, making it extremely dangerous for greenhouse operations.

Reproduction of the pathogen occurs via conidia formed in special structures called acervuli. These often have characteristic setae, which are an important diagnostic feature during microscopic examination of samples.

Conidia are dispersed within crops by water droplets during irrigation or rainfall, as well as by insects and agricultural tools. The high adhesion of the spores allows them to effectively anchor onto the surface of leaves and stems even after brief contact.

The biology of the pathogen allows it to quickly shift from vegetative organs to generative ones, which often leads to total crop loss in the absence of timely intervention by an agronomist.

A key factor in the development of Colletotrichum hsienjenchang is high air humidity exceeding 80–90 percent. It is under these conditions that the pathogen's spores germinate as quickly as possible, forming appressoria to penetrate the plant's epidermis.

The optimal temperature range for the development of the fungus is between +22 and +28 degrees Celsius. Sharp temperature fluctuations and heavy dew contribute to disease outbreaks even in the absence of direct precipitation.

Poor ventilation in greenhouses creates "stagnant zones" of humid air, where colonization by the pathogen occurs in a geometric progression. Dense plantings that hinder the evaporation of moisture from leaves provide an ideal environment for epiphytotics.

The presence of free moisture on the surface of plants for several hours is critically necessary for the infection process. Without water, fungal spores are unable to germinate and penetrate the host plant's tissues.

Agronomic errors, such as excessive application of nitrogen fertilizers, lead to the growth of loose tissues that are more easily penetrated by fungal hyphae, making crops more vulnerable to the pathogen.

Anthracnose causes colossal economic damage, reducing crop yields by 30–70 percent in years with weather conditions favorable for the disease. Affected fruits are not suitable for transport and rot quickly during storage.

The infection leads to premature leaf drop, which sharply reduces the plant's photosynthetic surface. As a result, carbohydrate metabolism is disrupted, and fruits do not achieve the necessary flavor and commercial qualities.

The loss of commercial appearance of vegetable produce entails direct financial losses. Retailers and processing companies refuse to purchase products that have even minimal signs of ulcerous damage.

The pathogen can completely destroy seedlings in greenhouses, leading to planting delays and the need for additional costs for replanting. Restoring soil balance after infection requires a long time.

The long-term survival of the fungus in the soil makes it impossible to grow susceptible crops on the same field for several years without expensive disinfection measures.

The basis of protection is compliance with crop rotation, excluding cucurbit crops from the field for at least 3 years. This allows the pathogen to lose its main food source and reduces the soil's infection background.

Using only certified, treated seed material is a crucial step. If seeds are collected independently, it is necessary to heat-treat them or apply fungicides recommended for controlling Colletotrichum.

Regular ventilation of greenhouses and maintaining optimal humidity levels suppress the fungus. Irrigation is recommended to be carried out exclusively at the root, avoiding moisture on the above-ground parts of plants.

Upon the appearance of the first symptoms, it is necessary to apply systemic and contact fungicides based on copper, strobilurins, or triazoles. It is important to follow the application regulations to avoid the development of resistance in the pathogen.

• Removal and destruction of plant debris immediately after harvest.
• Use of varieties with genetic resistance to anthracnose.
• Timely removal of infected leaves and fruits from the site.
• Disinfection of greenhouse structures and gardening tools.