Symptoms and Economic Impact

Symptoms

In Foliage

RZM in foliage

Rhizomania symptoms appear in patches in the fields and are visible with the naked eye. Rarely do infections cover the entire canopy. Symptoms include:

  • Wilting of the foliage, usually during the hottest part of the day in June
  • A pale, greenish-yellow color in the foliage (called Blinkers) during the later summer months
  • Newly produced, narrow leaf blades with long, upright stalks
  • A yellowing and necrosis of leaf veins. While this symptom is the reason for the name Beet Necrotic Yellow Vein Virus, it’s very rare to witness actual vein decay. The virus traditionally affects and remains in the roots hence the name Rhizomania, or “crazy root.”

In Roots

RZM infected root

Rhizomania inhibits the plant’s ability to absorb water and nutrients such as nitrogen or potassium. Root symptoms generally become visible only at the end of the growth cycle. Symptoms include:

  • Girdling of the lower part of the root
  • Random development of dense, dark root hair. These rootlets eventually dry up and turn from white to brown. As a result, new roots are continuously forming. This simultaneous growth and discoloration has been called a “salt and pepper beard” in some parts of the country.
  • Browning and death of vascular rings inside the root
  • The formation of perpendicular lateral roots

Diagnosis

Rhizomania symptoms are fairly easy to detect. Symptoms generally appear in the leaves. Inspection of the roots will confirm or rule out the diagnosis. The following list highlights some other afflictions that share similar symptoms to Rhizomania.

  • Wilting Leaves – This is the result of poor water intake. Deficient water intake can be caused by a variety of things such as other diseases, pests, water stress, etc.
  • Yellowed Foliage – Often times, the yellowing of leaves translates to a lack of nitrogen. However, sometimes yellowing can occur through viruses transmitted by aphids. If this is the case, leaves will become hard and brittle.
  • Irregular Root Hairs – The proliferation of root hairs can also be caused by a severe outbreak of nematodes. The outbreak is characterized by white cysts. The absence of cysts most likely means the plant is infected with Rhizomania.
  • Perpendicular Lateral Roots – The appearance of these roots is due to poor soil structure or an attack by the soil fungus, Aphanomyces cochliodes.

Economic Impact

The severity of the economic impact depends on a combination of things such as the variety of sugarbeet, the amount of Polymyxa betae in the soil, the strain of BNYVV, climactic conditions and the period of infection. The following crop loss and subsequent revenue loss is common for moderate to severe cases.

  • 2-4% loss of sugar content
  • Up to 70% loss in yield
  • Significant increase in soil tare
  • Reduced extractability due to an increase in sodium and inverted sugar contentGreater risk of repeat infection due to Rhizomania build up unless new Rhizomania-resistant varieties are used

Contents

Rhizomania
1. Introduction, Domestic Rhizomania, Geographical Distribution, and Epidemiology
2. Symptoms and Economic Impact
3. Disease Control and Resistant Gene Management
4. Summary

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