Their vigorous roots resist nematodes, and thrive in a wide range of soils. As grafting bases, they tend to dwarf the desired variety, and increase yield per acre. But now, for the last 20 years at least, we've had other ways to get around citrange muleism, techniques falling under the broad category of genetic engineering. But nobody is doing anything about engineering hardy citrus varieties. Take Florida, for instance, in the United States.
Citrus is the second largest industry in that almost tropical state.
The federal government and tax paying Floridians spend hundreds of millions each year breeding and testing new citrus varieties, inventing fresh ways of augmenting the Florida Citrus market image, and creating innovative processes to get citrus from the fruit tree to the gullet in novel, catchy ways. A Poncirus hedgerow planted along a chain link fence. There is a contorted, grossly convoluted dwarf form called 'Flying Dragon'. They seem almost a genetic gift from a Higher Being to a world fast reaching human saturation. The philosophy of sustainable agriculture demands that we use this gift to bring rich citrus nutrition to a hungry, minimally assetted world.