Alphanecrovirus

The primary signs of infection are localized necrotic spots appearing on the leaves, stems, and roots of affected plants.

At the beginning of the infection process, the spots may be small, brown or tan in color, and are often surrounded by a chlorotic halo.

As the disease progresses, the necrosis merges, leading to premature drying of the leaves and a serious reduction in photosynthetic activity.

On the roots, the infection manifests as tissue browning and suppression of the root system, rendering the plant vulnerable to other rots.

Visually, symptoms can mimic fungal leaf spots, which is why laboratory PCR testing or ELISA is often required for accurate diagnosis.

Alphanecrovirus is a genus of viruses within the Tombusviridae family, belonging to the group of phytopathogens with a single-stranded RNA genome.

The most studied member of this genus is the Tobacco necrosis virus (TNV), which serves as the type species for this taxonomic group.

These viruses possess small icosahedral virions lacking a supercapsid, which contributes to their high survival rate within the soil environment.

The pathogens are characterized by a broad host range, infecting both ornamental and agricultural crops in many regions of the world.

Transmission occurs non-specifically through the soil, most frequently involving the zoospores of the soil-borne fungus Olpidium brassicae, which acts as a vector.

Virus development is favored by high soil moisture, which facilitates the active reproduction of the fungal vector Olpidium brassicae.

Optimal temperatures for the infection process are generally in the range of 15–22 degrees Celsius, corresponding to periods of cool weather.

The infection easily persists in plant debris within the soil, where virions can remain viable for many months.

Frequent irrigation and water stagnation in fields significantly increase the risk of mass infestation by alphanecroviruses in both greenhouse and open-field conditions.

The use of contaminated substrate or seedlings grown under non-sterile conditions is the primary factor in spreading the disease to new areas.

Alphanecrovirus causes significant economic damage by triggering stunted growth and poor development in agricultural crops.

Damage to the root system leads to a reduced ability of the plant to absorb nutrients and water from the soil, negatively impacting crop quality.

In cases of early infection in young plants, complete crop loss or critical yield reduction is possible, making commercial cultivation unprofitable.

The disease is often accompanied by secondary bacterial infections that develop in necrotized tissues, worsening the overall plant condition.

On ornamental plants, the virus causes a loss of market value due to the appearance of necrotic spots, preventing their sale in the flower market.

The primary control method involves using healthy planting material and adhering to strict crop rotation with non-host species.

Soil and substrate disinfection, as well as the sterilization of greenhouse equipment, play a vital role in preventing virion transmission.

Managing the fungal vector Olpidium brassicae with specific fungicides can slow the rate of infection spread within greenhouse environments.

It is necessary to timely remove plant debris from the plot, as it serves as a reservoir for the pathogen to overwinter in the soil.

• Compliance with phytosanitary regulations
• Thermal treatment or fumigation of soil mixtures
• Utilization of virus-resistant varieties and hybrids
• Soil moisture control to limit the vector