Murahilin, curious as to why it's so important to you where Julie mango originated? Ok, let us know when you find conclusive evidence.
From the little research i've done i think it's hard to find such conclusive evidence, as plant material was carried freely between places and back again. Because mangos in Reunion have some DNA similarity doesn't necessarily mean they originated there. May just mean some of its parentage may have come from there. I don't think DNA alone can conclusively prove parentage, only relationship. You still need historical records + DNA thumbprints.
I suppose it's possible that mango seeds traveled from Africa during times of slave trade to Jamaica. But Reunion is off the wrong coast. So Julie would have to have been dispersed through Africa towards west coast to have been carried to Jamaica.
Oscar
Oscar,
My only reason is because I hate the idea of not knowing. There has to be an answer, and I am sure there is record of it somewhere. I don't know if I will ever find conclusive evidence, but I will continue to search.
I agree that it may not have originated in Reunion, but that one source from the 1960's saying that it did is interesting. I am going to try and get in contact with the author of that article (I was told he is still alive) and see if he remembers why he thinks that Julie originated in Reunion.
I doubt it came through Africa though for the same reasons you mentioned. I think it is more likely that the Julie or its ancestor mangos went directly from Reunion to one of the French Caribbean Islands and then either the Julie grew there or the Julie's ancestors further spread into the Caribbean and finally created the Julie in Trinidad. I haven't found any evidence supporting Jamaica as the origin yet though. Everything seems to point to either Trinidad or Reunion.
Another interesting side note, Trinidad had a fruiting mangosteen in 1875.