Beet necrotic yellow vein virus genome reassortments in a resistant sugar beet variety showing – in a small area in France – strong rhizomania symptoms

The genome composition of Beet necrotic yellow vein virus (BNYVV) was analysed in rootlets of field-grown sugar beets belonging to a variety which in spite of carrying the Rz1 resistance gene had developed strong rhizomania symptoms in a small area of France. This area was located in a borderline region between the distribution areas of P type BNYVV on one side and of A and B type BNYVV on the other. All five samples contained P type RNA 5. RNAs 1 to 4 were derived either solely from the A, B or P types or from mixtures of B and P types. It remains to be shown whether or not these RNA reassortments are responsible for the observed resistance breaking. By means of immunosorbent electron microscopy other sugarbeet viruses, i.e. Beet soil-borne virus, Beet virus Q, Beet mosaic virus, Turnip mosaic virus or Beet black scorch virus were not detected in these samples.