Is it possible to make an orange tree produce sweeter oranges?

Answer 1

No, not possible. But maybe you could breed for sweeter oranges by crossing trees that produce sweet oranges. The process would take you quite some time.
And you can't splice an orange and a sugarcane plant. Sugarcane is a grass, oranges are not. Beside, what would that do anyway???!!!

Answer 2

Commercial growers try all kinds of mixes of orange properties (man-made evolution to reach an optimum). However sweetness is only one trait they try to enhance. Given a choice between making an orange tree that has a heavy crop with a hard-to-bruise-skin, resistance to frost, and that all ripens at the same time to make harvesting easier then your sweetness trait gets to be low on the list.

When they find oranges with features they like they take cuttings to clone the trees they are on so lots of mixtures are possible - but are they desirable?

Answer 3

You cannot tamper with the genetic make-up of this plant,it will continue to yield the same type of fruit as it does now,trying to graft on to it a scion of a sweeter orange bearing plant is a dubious procedure,the practical step would be to grown a plant recommended by a reputable nursery,research is breeding into fruit many desirable qualities.

Answer 4

Well you could (seriously) try to make a hybrid orange tree by hybriding it with a sugarcane plant