Why is bananas not considered as a hybrid fruit? And no isur of klaiem?
Bananas are permitted for us to eat. On one hand our bananas are a hybrid of two different type of bananas, and it is possible that the prohibition of kilayim won’t apply to the mixture of the two of them, but this point I don’t know. The main reason it is permitted though, is that even though they do originally come from grafting, however the fruits that we are eating are not from the actual grafted trees, but from replanted produce of these trees. The replanted produce of branches of these trees that were replated are not forbidden to eat. Additionally they most probably were planted by a non Jew, and therefore not an issue, therefore they are permitted to eat without a problem..
Rambam HIlchos KIlayim 1-3, 7, Y:D 295-7.