Diseased Clematis
 

We got a few clematis seeds, free with a magazine and one of them grew &
flowered with some marvelous large purple flowers. However, it began
showing signs of disease from the base and slowly worked it's way up until
eventually it was engulfed. This whole process took around 6-8 weeks.

http://www.flickr.com/photos/16402628@N00/25165269/

Any ideas what this is and how to avoid it in the future? Also, can the
plant be cut down to grow again cleanly or is it lost?!!

TIA