That's why it's understandably frustrating if you have tried your hardest with a particular fruit tree and it shows no signs ...

A version of this story appears in the February 2017 issue of National Geographic magazine. Citrus, in many ways, stands alone. So many cultivated species have come from so few primary ancestors.

Most citrus trees that come from the nursery are grafted. That means that they are made by splicing two different trees together: a rootstock and a scion (the portion of the tree that bears fruit).

We’re on the edge of something special. Florida citrus is making a comeback, one tree at a time. I am running to the fight to save Florida citrus, and I ask you to join me in that fight.

Today, nearly every citrus grove in Florida is infected with the disease. If an orange tree were to remain untreated, the disease would block its ability to get nutrients and kill it within a few ...