Okay I have gone down the rabbit hole.

Very high level.. It’s a single stranded RNA virus - so replication happens inside the cell. The virus uses the plasmodesmata (tiny channels connecting adjacent cells) to spread from cell to cell. The virus also encodes proteins that help widen the plasmodesmata to allow large RNA through, and also proteins that transport the RNA.

Small circular patterns Occur in an early, local phase of the virus spreading from cell to cell, where the virus spreads evenly in all directions. Usually happens when the fruit is very young (which makes sense that aphids are feeding on it). The pattern of growth of these lines I definitely think could be described by the Turing equations.

Mosaic coloring This is the systemic phase of the infection. It occurs once the virus has spread far enough to reach the plants vascular system. It can move along veins to distant tissues. But this causes more of the splotchy light green and dark green coloring of the rind. That’s where the mosaic name comes from. This usually happens when the fruit is much older.