What is the hottest breed of horseradish?

I used to think that they used the hottest horseradish they could find for the American wasabi condiments that are super hot. That (and because I like the hot wasabi) inspired me to ask the initial question. However, after some research today, it looks like they might use hot mustard (perhaps black-seeded mustard) to make it hot. I know that real wasabi isn't supposed to be that hot, though.

I also have a suspicion that horseradish grown in full sun might be hotter than regular horseradish. My friend who gave me roots said this was a mild kind (he did grow it in a shaded area, though, and watered it a lot, by the sound of it; so, I wonder if it's the way you grow it as much as the breed that makes the difference). They say horseradish likes full sun, but tolerates partial shade. We're planning to give it some shade as recommended by my friend, this year (he gave me some horseradish to grow), but we may transplant some to full sun another year.

[HASH]wasabi [HASH]mustard