Anthracnose

The primary sign of anthracnose caused by Colletotrichum paxtonii is the appearance of small, sunken spots of brown or black color on leaves and stems. Over time, these spots may merge, forming large necrotic patches.

Under conditions of high humidity, characteristic pink or orange pustules appear on the infected areas, representing the fungus's sporulation. This is a key diagnostic feature during visual inspection.

On stems, the disease often manifests as deep ulcers, which can lead to constrictions and subsequent plant lodging. The affected organs lose turgor and gradually wilt due to the disruption of the transport system.

Fruits or berries infected by this pathogen develop wet, dark spots that spread rapidly. In the center of such spots, a sporulation zone is often observed, which leads to the degradation of the produce's commercial value.

When the root collar of seedlings is affected, rot develops, often leading to the complete death of young plants in nurseries or greenhouses. The root system in such cases turns brown and dies off.

The causative agent of the disease is the microscopic fungus Colletotrichum paxtonii, which belongs to the class Ascomycetes. This pathogen is a specialized parasite that primarily attacks plant tissues during the growing season.

The fungus spreads actively through conidia, which are asexual spores formed in specialized structures called acervuli. These structures often rupture the plant epidermis, facilitating the release of spores into the external environment.

The infectious material survives in plant debris, soil, and on seeds in the form of mycelium or sclerotia. This makes the pathogen extremely resistant to adverse environmental conditions.

The life cycle includes the germination of conidia upon contact with a moist leaf surface, followed by the formation of an appressorium for penetration into host tissues. The penetration process is accompanied by the secretion of specific enzymes that break down cell walls.

The fungus is capable of rapid colonization of the intercellular space, leading to the formation of necrotic areas. Under conditions of high humidity, the development of the mycelium inside the infected organs accelerates significantly.

Optimal conditions for infection include high air humidity (above 85-90%) and moderately warm temperatures. Regular rainfall and dew promote active spore germination and their movement onto healthy tissues.

Dense plantings that impede normal air circulation and promote the accumulation of moisture droplets create an ideal microclimate for disease outbreaks. Proper field ventilation is a critical factor in reducing infection risks.

Improper irrigation, especially overhead sprinkling in the evening, significantly increases the risk of anthracnose infection. Prolonged moisture on plant surfaces allows spores to successfully anchor and begin the penetration process.

The presence of damaged plant tissues caused by pests or mechanical injury during maintenance significantly facilitates infection. The fungus primarily utilizes micro-cracks to colonize the plant.

The temperature optimum for the development of Colletotrichum paxtonii varies between 20-25 degrees Celsius. However, the pathogen can remain active across a wide temperature range, extending its harmful potential.

The primary harm lies in the sharp reduction of photosynthetic activity due to the death of leaf surfaces. Plants lag in growth, and the intensity of generative organ formation and development decreases.

Infection of fruits makes them unsuitable for storage and transportation, leading to direct economic losses. Infected produce rots quickly and can serve as a source of infection for neighboring healthy fruits.

Massive spread of the disease in fields leads to a total yield reduction of 30-50% or more. In cases of epiphytotic outbreaks, losses can reach critical levels, making harvesting economically unfeasible.

The infection negatively affects the seed quality of the harvested produce, reducing germination rates and vigor. Using such seeds in the next season leads to the infection of new areas.

Severe infection of stems and roots provokes premature plant death, which is particularly dangerous for perennial crops. This leads to reduced stand density and the need for additional remedial work.

Prevention begins with crop rotation, ensuring the same crop is not returned to the field for at least 3-4 years. Thorough incorporation of plant debris into the soil promotes rapid decomposition and the destruction of the fungus.

The use of resistant varieties and hybrids is the most effective biological method of control. It is recommended to purchase only high-quality, certified, and treated seed material.

During the growing season, it is necessary to conduct regular spraying with contact and systemic fungicides. The choice of products should be based on the current plant growth stage and weather conditions.

An important technique is timely control of insect pests, which transport fungal spores and damage the epidermis. Optimization of mineral nutrition, especially avoiding excessive nitrogen doses, increases plant immunity.

In greenhouses, disinfection of premises and tools, along with maintaining an optimal humidity regime, is mandatory. Upon detection of the first signs of the disease, immediate isolation and removal of infected plants from the greenhouse are required.