CTV-SP is only caused by some isolates of CTV.
CTV is a member of the closterovirus group of plant
viruses with long flexuous rod-shaped particles. CTV
is the largest plant RNA virus that has been
characterized. There is extensive genetic diversity
among various isolates of CTV and many genetic
groups of the virus have been found. Variability also
exists within each group. The specific regions of the
virus genome that are associated with the induction
of stem pitting have not yet been identified.