Step 4: Leaf Scale

The pattern of the yellowing is definitely interveinal chlorosis.  The most severe symptoms are in the newest emerging leaves.  There are no necrotic leaves.

When examined more closely, the roots still are generally white on all affected plants, with some showing a slight tan discoloration.

 

Calibrachoa showing interveinal chlorosis.

The most severe symptoms are in the new growth of Nemesia.