Corruption cannot be the no 1 reason for a country being poor. You can even make a point that corruption is an effect not a cause, i.e. corruption is rampant when a country is poor. Corruption is found everywhere, including the rich developed countries.

I haven't done any research on this subject so cannot tell you what the cause is but there has to be a reason why a society adopts corruption to a scale that it is uncontrollable. It is more than education. I do believe it trickles down from top to bottom. A good legal system (constitution plus bylaws) and a solid enforcement of this is definately the cure for both economical and corruptional issues.