Pears ( Pyrus ) represent an important part of consumer diets, and have the fourth highest production of non-citrus fruits, measured by fresh weight, in the U.S. They are maintained clonally and grown as composite plants, consisting of a scion (fruit bearing) cultivar grafted onto a rootstock cultivar. Up to 98% of existing production relies on only a few scion and rootstock cultivars, leaving the standing crop vulnerable to t...