Plum witches broom virus

Plum witches broom virus (Grablovirus pruni) is a serious viral disease affecting stone fruit trees, particularly those within the Prunus genus. The pathogen causes systemic infection, leading to drastic physiological disruptions, severe morphological deformations, and a long-term decline in the health and reproductive performance of the affected plants.

This virus primarily infects plum trees and related species such as cherry plums. Once the virus enters the vascular system of the tree, it systematically spreads to all parts, making the tree a permanent reservoir of infection that can affect surrounding plants over time.

The characteristic symptom, often referred to as a "witches broom" effect, involves an abnormal clustering of thin, weak, and shortened shoots at the ends of branches. The leaves become noticeably deformed, often taking on a lanceolate shape, exhibiting chlorosis, and failing to develop normally, which significantly reduces the tree's ability to undergo photosynthesis.

The transmission of Grablovirus pruni in orchards is primarily facilitated by sap-sucking insect vectors, including aphids and eriophyid mites. In addition to insect transmission, the virus is spread through human activities, specifically the use of infected graft wood during propagation and the mechanical transfer of sap via contaminated pruning tools used on healthy trees after contacting an infected one.

The economic impact of this disease is severe, as infected trees show a drastic reduction in fruit yield and quality. Fruits may be deformed, stunted, and fail to ripen properly. Because there is no chemical cure for established viral infections, the disease eventually renders trees unproductive, necessitating their removal to prevent the further spread of the pathogen within the orchard.

Management and prevention strategies focus on limiting the introduction and spread of the virus through strict adherence to horticultural hygiene:

• Source healthy, virus-indexed plant material only from certified nurseries.
• Implement robust integrated pest management (IPM) to control insect vectors like aphids and mites.
• Sterilize all pruning tools with a disinfectant solution between trees to prevent mechanical transmission.
• Rogue out and destroy symptomatic trees as soon as they are identified to remove the source of infection from the orchard environment.