In eight interspecific and intraspecific Malus crosses, segregation of seedlings after greenhouse inoculation with Erwinia amylovora indicated that resistance to fire blight was polygenically controlled. In certain interspecific and intraspecific crosses, high percentages of resistant seedlings were recovered suggesting that sources of fire flight resistance are available in the cultivated apple as well as in other small-fruited Malus species.
This work was supported in part by a grant from the Horticultural Research Institute, Inc., 1250 I street, N.W., Suite 500, Washington, D.C. 20005. Support was also provided by the Illinois Agricultural Research Station, project no. 65-325.