Beet necrotic yellow vein virus

Beet Necrotic Yellow Vein Virus (BNYVV) is a plant pathogen that primarily affects sugar beet (Beta vulgaris) crops, causing the disease known as rhizomania. This disease is characterized by a severe reduction in sugar yield and root quality due to the proliferation of rootlets, giving the root a "bearded" appearance, and is often accompanied by yellowing and necrosis of the vein tissues in the leaves. BNYVV belongs to the genus Benyvirus and is transmitted by the soil-borne fungus Polymyxa betae.

Discovery and Distribution

BNYVV was first identified in the 1950s in Italy and has since been reported in most sugar beet growing regions worldwide, including Europe, North America, Asia, and the Middle East. The virus's widespread distribution and the persistence of its vector, Polymyxa betae, in soil for many years, make rhizomania one of the most economically significant diseases of sugar beet.

Symptoms

The symptoms of rhizomania caused by BNYVV can vary depending on the stage of the plant's development, environmental conditions, and the virus strain. Common symptoms include:

• Stunted growth and reduced root size
• Excessive proliferation of rootlets, leading to a "hairy" root appearance
• Yellowing of leaves, starting from the vein tissue
• Necrosis of leaf veins in severe cases

Transmission

BNYVV is transmitted by Polymyxa betae, a plasmodiophorid that infects the roots of the sugar beet. The virus is taken up by the fungus from infected plant debris in the soil and then transferred to healthy plants during the fungal infection process. The virus can persist in the soil for many years, as it remains viable within the resting spores of Polymyxa betae.

Management

Management of rhizomania focuses on preventing the spread of BNYVV and reducing its impact on sugar beet crops. Strategies include:

• Use of resistant sugar beet varieties
• Crop rotation with non-host plants to reduce Polymyxa betae populations in the soil
• Sanitation measures to prevent the movement of contaminated soil and plant material
• Chemical control of Polymyxa betae has been explored but is not widely used due to environmental concerns and the risk of resistance development

Genetic Structure

BNYVV is a multipartite virus with a genome divided among four to five RNA segments, depending on the strain. The RNA segments encode for several proteins, including the coat protein and the RNA-dependent RNA polymerase, which are essential for the virus's replication and assembly.

Economic Impact

The economic impact of BNYVV on the sugar beet industry is significant, with losses due to reduced yield and sugar content. In areas heavily affected by rhizomania, the use of resistant varieties has been an effective strategy in mitigating losses, but the emergence of resistance-breaking strains poses ongoing challenges.

Research and Future Directions

Research on BNYVV continues to focus on understanding the virus's molecular biology, the interaction between the virus and its vector, and the mechanisms of resistance in sugar beet. Advances in genetic engineering and breeding techniques offer promising avenues for developing new resistant varieties and potentially more sustainable management strategies for rhizomania.