Scientists and historians estimate that more than 14,000 varieties of apple have been cultivated in the United States, but over the past 100 years, much of that diversity has been lost as agriculture shifted its focus to large-scale production of just a few types. Today a mere 11 varieties account for more than 90 percent of all domestic apple sales. The good news is that researchers at the University of Arizona and the U.S. Department of Agriculture have recently identified 110 genetically unique types of apple on abandoned homesteads in the Southwest. The newly rediscovered heirloom varieties have survived for decades in the arid Southwest, indicating that they may contain genes that confer resistance to dry weather -- an important trait that could come in handy for apple breeders if climate change increases the frequency or severity of droughts.