If the scientist creates a plant with trait X from the use of licensed CAMBIA materials and the university wishes to commercialise it, are we are obliged to provide CAMBIA with these materials...?

No.  A plant created for commercialisation that doesn't meet the definition of an enabling technology also wouldn't meet the definition of Improvement in the license, and the Tech Support Agreement provides for distribution of materials only in  relation to Improvements that are not  Products.  The rather complex definition of "Improvement" in the License versions 1-1.5 was purposely designed to maintain wide capabilities of sharing the use of technical improvements to the technology while still being as supportive as possible to entities that are involved in delivering products to the marketplace, whether via for-profit or public good mode.