I think it is just scabbing over from broken sprouts. The smaller ones will grow. It sure doesnt look like any type of rot that I have seen.

Tubers quite often sprout while in storage. Most vendors cut off the sprout before shipping. They do this because the sprout will often fall off during shipping. When this happens, customers get worried that the tuber is now dead and contact the vendor for new one. Dahlias almost always sprout again from the same eye or another eye and this is a good picture of that process.

Thanks for your helpful answers.
I guess I am slightly paranoid because I kind of started a collection this season (picked about 20 new cultivars which is a big leap for me) and I was just worried that this wasn`t an early stage of crown gall or something nasty.

And yes, it did sprout, I marked the pott and it sent up two nice shoots.

So a great Dahlia season to you, bye, Lin