If it's not too late, you might try re-framing the question. Instead of "Who was the first..." try one of these:
When did that style of play begin to become popular in jazz? What style did it supplant? In what other styles of music was it already used and might they have influenced the adoption of pizz? Was there any influential alternate style (was bowing ever really popular?) Were there any non-western musical traditions or instruments that may have supported the introduction of the bass used in this way? Were there listener expectations that may have led to it? Did the circumstances of performance favor that style of play? What was the impact of recording, if any, on the rise in popularity of that style?
You can probably answer the 'who' question by coming at it from any one of those.
Ummm, did you say this was you dissertation topic
A fun topic in any case.
John
