The character is living in a world where grass is extinct. He works on a particular species of grass, researching and trying to reproduce it in the lab (but it is difficult because the cultures he is using are very very old).

Does the above sound semi-correct? For this particular story, I don't need to go into details of his research - so it's ok that I know next to nothing about grass I just want an ok sounding thesis statement.
 

In vitro regeneration of Lolium perenne

Your original thesis title would be fine if there were other people working on other types of grass and other people using different methodologies/source materials but working on the same grass.

If you mean more than a title, by the term "statement", then in a thesis, an abstract or proposal would be more appropriate, which is more the size of a paragraph.

However, it is your world, so you don't have to be kept to current expectations.

One final point, if you do go for your current statement, the term "ancient" is perhaps not precise enough for the rest of the statement, and a period statement (e.g. nineteenth century) may be better.
 

The effects of Streptozotocin-induced diabetes on latency to seizure in rats.

Its very easy to get an idea of what a thesis title should look like though. Just go here:

http://www.ncbi.nlm.nih.gov/pubmed

and type in anything you want. You could use lolium perenne, for example. These are trade journal publications, but because graduate students often publish an abridged version of their thesis in trade journals, they will title them like a journal pub.