I'll take a stab at this....First of all, is this something that you specifically bred? You took two parents and crossed them, and you feel that you have something unique? Were the parents patented varieties? Was this a random cross that just appeared? Can you duplicate it? What is special about it? Is it a unique color or habit? You have to realize that there are dozens of plant breeding companies that are developing new lines of petunias for commercial production from both seed and cuttings every day. I don't want to discourage you, but it is probably more involved than you are prepared for.

This was a cross that appeared after having 2 different petunia varieties in the same pot on my back deck. The parents were both form the "Suppertunia" breed. I am attempting to duplicate it again, and am planning to collect seeds. The color is beautiful and spectacular, an I think that it must be my favorite petunia I've ever seen. (Although I probably unfairly favoring it because it happened to appear in my flower pot and also it is the offspring of my two favorite patunias, and therefor in my exact favorite colors. LOL) What I'm thinking of doing is collecting seeds and seeing if I can grow it for several years, and then, if I'm up for it, trying to register it. Is this an appropriate course of action?

Supertunias are propagated vegetatively, and are patented hybrids. If your plant produces stable progeny from seed (unfortunately, pretty unlikely), and you can produce several generations of it, it may be worth pursuing. What I would recommend is taking cutting of your plant and rooting them to produce more of your plant, and just enjoy them that way. Getting it patented commercially is pretty involved. I guess the question to you is, what do you hope to achieve by "registering" it?