Great ideas everyone. Fruitforme, please keep us updated, you could save some of us a lot of time. If one or two of your grafted varieties takes on your Longan rootstock, that would lead me to believe that the Lychee and Longan are more compatible than we thought.
This also makes me wonder why we haven't heard more about Lychees grafted onto Longan? There must have been others that have tried this, I'm sure I've read it somewhere but perhaps the benefits of the grafted plants aren't as beneficial as believed or the cost and labor are too high for commercial production. I wonder if there is any papers on long term compatibility? If the grafted trees are fully compatible and vigor is conveyed, I would expect many Lychee farmers to be using this technique. Perhaps it would be more beneficial to farmers living in the USA growing in high pH soil? I bet Bill Mee would be interested.
I wonder how a multiple rootstock, one Longan rootstock one Lychee rootstock, Lychee tree would do. Perhaps more is not always better but why wouldn't an extra Lychee rootstock prove beneficial?
Simon