Ok, I have dealt with a lot of stuff like this (and have now owned 5 Defender cabinets).
Several options.
#1. Replace the entire peice of wood. (Harder then you might think).
#2. Wood putty. Not tood hard, although it is never going to look perfect unless you are VERY experienced with that sort of thing.
#3. What I do with lower cabinet damage. I make kick plates, I make them on all 3 sides if needed. Just go to a big hardware place and find an appropriately sized piece of aluminum trim of any kind (I have also used wood trim). Use a hacksaw to cut it to size and then paint it black and install it on the cabinet.
Lately I have also been putting corner protectors from Bob Roberts on ALL my new projects. Lets face it, the bottom of these cabinets get JACKED up. The 3 in one combination of corner protectors, a kick plate in front, and corner trim at the bottom of both sides will prevent damage and hide current damage.
Well done trim always looks better than damage. I have had plenty of game EXPERTS over at my place, and have never had so much as a mention of any of my "non-original" trim.