Benyviridae

The Benyviridae family consists of plant-infecting viruses characterized by a multipartite, single-stranded RNA genome and rod-shaped virions. The most significant member of this family is the Beet necrotic yellow vein virus (BNYVV), which is responsible for the devastating rhizomania disease in sugar beet crops worldwide.

These viruses are uniquely transmitted by the soil-borne plasmodiophorid Polymyxa betae. The virus persists within the resting spores of this protist, which are exceptionally hardy and can survive in the soil for over a decade. Consequently, once a field is contaminated with these viral particles, it remains a long-term threat to subsequent susceptible crops.

Infected plants display distinct symptoms, including yellowing and necrosis of the leaves, accompanied by stunted growth. A hallmark diagnostic sign is the proliferation of fine lateral rootlets, commonly referred to as "root beard" or rhizomania. This destruction of the vascular system prevents the plant from absorbing nutrients, drastically reducing sugar content and root size.

The spread of the disease is highly dependent on environmental factors, particularly soil moisture. Optimal conditions for virus transmission occur when soil is saturated, allowing the zoospores of Polymyxa betae to swim and infect the root hairs of host plants. Additionally, the movement of infested soil by farm machinery, irrigation water, or flooding events significantly accelerates the dissemination of the disease.

The economic impact of Benyviridae infection is profound, often leading to total crop failure or severe yield losses. The reduced sucrose content in infected sugar beets makes the harvest economically unviable for sugar processing factories, forcing farmers to abandon infested fields for many years.

Management of Benyviridae is challenging due to the persistence of the vector in the soil. Effective control strategies involve an integrated approach:

• Planting resistant or tolerant sugar beet varieties.
• Improving field drainage to discourage vector activity.
• Sanitizing farm machinery to prevent cross-contamination between fields.
• Implementing long-term crop rotation to manage the population density of the soil-borne vector.