Rebutia are some of the few cacti I've played with, love those little critters! I've just been thinking about working with them again when they bloom here.

>>"In order to get a hybrid true to form (meaning that 100% of the seeds will produce the same traits as the hybrid) I have to continue to only pollinate the hybrids that are true to the hybrid traits until eventually the seeds will become "true to form"."

This is true- but "true to the hybrid traits" can mean just about anything. Here's how that works:

If both of your plants are natural species, then your first cross hybrids will all come out about the same- something like both parents. But, once you cross or self-pollinate a hybrid, the "F2", next generation, can show all kinds of traits and every one of them might be different. Then, you choose the one you want most, and self-pollinate that one. You'll probably still get a lot of variation. Do it again with the one that looks most like what you want. It usually takes several generations to stabilize a seed strain so they start coming up all similar (but may take a very long time before they are identical!)

That's called inbreeding. If you like, you can inbreed two separate ones that look just like you want, and after those are stabilized, cross those two. That's called line breeding, and can (possibly) give stronger more vigorous plants. Really though, as long as you are careful to only choose vigorous and floriferous plants to continue with, inbreeding is fine- and faster.

If either one or both of your parent plants is a hybrid, then you're starting at the second step- the seedlings will have random assortments of genes and be a mix of different colors and forms. You never know what you're gonna get.

Because of all that effort and time involved, most hybrids are reproduced by cloning (cuttings/division) only. Even after you've gone through years of stabilizing a strain, seedlings can result in genetic drift, and possible outcrossings, so future generations with your chosen name on them might not end up being very different anyway.

>>"Will the flowers on my hybrid become sterile from this?"

If both parents are closely related Rebutias, then you will probably have no problems there. Rebutia hybrids can be fertile.

>>"If so, how is it possible to keep the hybrid producing seeds so that I may one day get the seed true to form?"

If you end up with a sterile hybrid, you're pretty much stuck there. It MIGHT be possible to continue by embryo rescue, or converting the pollen or plant to tetraploid, but those are mostly laboratory type procedures.

>>"Will the flowers being self fertile counter act the sterility?"

No- they'll be the same level of fertility to both crossing and selfing.

>>"Or are there only a small percentage that will/wont be sterile?"

Again that depends on the genetic compatibility between the parents. A hybrid is either sterile, fertile, or weakly fertile (produces fewer seeds with more effort). The whole plant will have the same fertility level.

Even "sterile" hybrids of many plants can be rarely and weakly fertile though, I've seen it in wide crosses from other plant families. I don't know how common in cacti though. Once you manage to get seed growing from a difficult cross, the later generations tend to be more fertile again.

Strongly self-fertile plants can be difficult to cross. You'll want to look up how to emasculate flowers- removing the anthers before the flower is open, and then covering the stigma to keep insects away until after you've put on the pollen from the other parent. You do not need to have self-pollination in Rebutia to make your crosses, it just gives you mostly redundant plants.

If down the line you get plants that are very different from what you're working on, and you have any other related flowers (or stored pollen) around, don't label them as the same cross. It's possible that they accidentally got something different in there. It's better to call them unknown crosses than to have the wrong information attached.

Please be sure to discard any plants that look much like the original species- keeping them can result in polluted gene pools despite best intentions!

Good luck and have fun!

Vincent