The University of Florida came out with a list of recommended varieties for Florida door yard citrus that are supposed to be more tollerent of greening. Sugarbelle was at the top of the list, but Persian Limes, Lemons, a California Manderin (Gold Nugget if my memory serves me), the "Jackson Hybrid" (a grapefruit type citrus), and Sundragon an orange hybrid with a "spicy" flavor that includes some poncirus genetics in its heritage also made the cut. They claim that with adequate fertilization and care, theses varieties can still be productive for the home owner in the face of greening. However, I have yet to see some of these offered for sale anywhere in Florida. Frequent compost applications and regular watering are also helpful from what I have seen. I can spot the groves using compost up here just by how the trees look most of the time.