Is the shortest circuit/cocircuit problem on transversal matroids or gammoids NP-hard?
Is there anything known about this?
It is known that the shortest circuit on binary matroid is NP-hard. But I can not find 
any reference on transversal matroids or gammoids.

This is a followup question of 
https://mathoverflow.net/questions/97517/a-minimum-set-hitting-every-base-of-a-matroid