After talking to a friend about all the lovely variegated plants up for sale in Asia and Europe he seems to think that growers are some how creating these variegated plants presumably by means of introduction of chemicals of a certain kind. After hours of searching the net for any information regarding this it seems we have hit a brick wall.
I would love to hear anyone's thoughts or experiences with variegated plants. I have had normal plants throw the occasional variegated offset also i have propagated haworthias from leaves and got a variegated offset these are very rare in my experience though.
Another interesting thing i have found that old seed if it germinates i seem to get on the odd occasional variegated seedling. There is a answer out there in regards to creating variegated plants just have to find it.

I strongly suspect that for commercial production of variegates a lot of cloning takes place. I suspect for the more unusual plants, tissue culture is the preferred method.

I have seen variegates appear naturally in large sowings of seed, however this would usually occur at rates of a fraction of a percent.

I used to think they just sow an enormous amount of seed and bin 99.99% of the seedlings and select the variegates, same as for monstrose cultivars etc, and breed/tc from there.

But I wonder how much intentionally produced via chemical eg colchicine application and radiation exposure

Lots of variegated agaves, yuccas and broms are tissue cultured, a quick google search reveals

http://www.bennyskaktus.dk/Yucca_variegated_forms.htm
http://www.smgrowers.com/products/plants/plantdisplay.asp?plant_id=3158
http://www.bcss.org.uk/foruma/viewtopic.php?f=1&t=70315

Here you go:
http://www.succulent-tissue-culture.com/EN/news


Though I thought that a lot of variegated plants were more difficult to grow reliably from TC as if you get the achlorophyllous tissue and culture that you will yield unviable albino plants?

Some variegated plants are also virus-infected, such as the vulgar Aucuba japonica variegata.

Seems radiation exposure is common in history and made many modern foodplants... might make you think twice about your food... pretty unnerving stuff:

"Though poorly known, radiation breeding has produced thousands of useful mutants and a sizable fraction of the world’s crops...including varieties of rice, wheat, barley, pears, peas, cotton, peppermint, sunflowers, peanuts, grapefruit, sesame, bananas, cassava and sorghum."

http://en.wikipedia.org/wiki/Mutation_breeding

Thanks for that Lewis. Some great info.

Actually CC re-reading that I think I may have overstated the induced mutations and i admit I have not researched how these particular production nurseries to which you refer actually operate, but it seems seed produced by variegated x parent plants esp of hybrid origin, may produce a high % variegated offspring (which can presumably be crossed further to enhance the prevalence) so no need for nasty chems/radiation treatment.
see here:

http://forum.auscactiforum.net/t1343-variegated-cactus-question
http://forum.auscactiforum.net/t1356p15-how-do-i-identify-variegated-seedlings

Also re: the t/c, perhaps they just use regular plants as stock tissue, then use certain techs to induce mutation (variegation) afterwards (easier than say using variegated stock tissue to begin with and producing many albino/solid green propagules). If you look at the succulent tissue culture and the bcss forum link they say that they can "make" anything go variegated. However, whether you'd want an entire collection consisting of plants that look virus-infected or with nitrogen-deficiency is I suppose a matter of personal preference..

talking about astrophytum asterias i can tell that if you use a variegated/albino motherplant a good part of the ofsprings are variegated and some are albino,the opposite cross give poor result but this is something that the japanese master cultivators of astrophytm thinks differentlly .....probably japanese cultivars act different from the cinese one that i have...

I have 2 variegated Astrophytum asterias. When I used them as mother plants and crossed another asterias, around 50% of seedlings were variegated.

I tried to make ruri kabuto nishiki (variegated ruri kabuto) and gave a question to a Japanese expart. He suggested ruri kabuto x variegated kabuto would give a better result, used variegated kabuto as a father plant.
I collected seeds made by crossing both ways in this year.

When you crossed Astrophytum which have different flower colors, you will get variegated seedlings also. This variegation is called "akebono-han" meaning twilight variegation made by the hybridization issue. Seedlings are very weak and slow growing or short life if you kept them as own-rooted plants.
It is possible to keep them if you grafted.

eg
asterias: yellow petals and orange throat (father)
capricorne: yellow petals (mother)
I normally dislodge these seedlings.
The photo is capricorne v niveum x super kabuto, grafted akebono-han.