Rhizomania, a serious disease affecting members of the beet family (Amaranthaceae), is caused by the beet necrotic yellow vein virus (BNYVV). This virus, classified as a furovirus, is transmitted by the soil-borne fungus Polymyxa betae, an obligate parasite requiring a suitable host to complete its life cycle. The viral pathogen survives in the fungus’s long-lived survival structures, known as cystosori. These structures release zoospores that infect beet roots and, if viruliferous, transmit the virus into the plant.Â
Disease symptoms:
Foliar symptoms
- Yellowing (chlorosis) of leaves, often confused with nutrient deficiencies or water stress.
- Systemic infections may lead to:
- Veinal necrosis.
- Crinkling, wilting, and stunting of leaves.
Root symptoms
- Affected roots exhibit a constricted taproot and the proliferation of small lateral, fibrous, hairy roots, creating a beard-like appearance (known as “bearding”).
- Key impacts include:
- Reduced nutrient and water uptake, stunted growth, and lower yield.
- Late-season infections can result in slender roots with a high crown, forming a “wineglass” shape.
- Severe cases may lead to dead taproots and lateral roots with light brown vascular tissue.
Favourable conditions for disease development:
The zoosporic nature of Polymyxa betae requires warm, water-saturated soils for effective dispersal and infection.
- Early infection: Leads to significant stunting and yield reduction.
- Late infection: Results in reduced sucrose content but may still allow acceptable root yields.
- The extent of yield losses is closely linked to the timing of infection.
Prevention and control:
Cultural practices:
Implementing cultural practices to disrupt the vector’s life cycle (Polymyxa betae) can reduce disease incidence and severity:
- Avoid soil spread: Prevent the movement of infested soil between fields.
- Optimal planting practices:
- Early sowing in cooler soil temperatures.
- Precise irrigation and proper soil drainage to reduce water-saturated conditions.
- Establish a dense leaf canopy to suppress infection.
- Crop rotation: While helpful as a precaution, rotation is less effective in fields already infested with Polymyxa betae due to the long dormancy of its spores.
 Resistant beetroot varieties: Using Rhizomania/BNYVV-tolerant F1 hybrid varieties is the most effective control method. However, recent evidence suggests some pathogen populations may overcome resistance, and these seeds are expensive.
 By combining the use of resistant cultivars with careful cultural management practices, growers can effectively reduce the impact of Rhizomania on their beet crops, safeguarding yields and quality.
Disclaimer
This information is based on observations and sources believed to be reliable. However, crop performance depends on the interaction of genetic potential, seed characteristics, and environmental factors, including management practices. Sakata Seed Southern Africa (Pty) Ltd provides no express or implied warranty for crop performance based on this information and accepts no liability for losses resulting from its use. Please refer to Sakata Seed Southern Africa’s Conditions of Sale before ordering seed.