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Relative Susceptibility of Succulent and Woody Tissue of Magness Pear to Infection by Erwinia amylovora . T. van der Zwet, Research Plant Pathologist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705; H. L. Keil, Research Plant Pathologist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 60:593-595. Accepted for publication 1 October 1969. DOI: 10.1094/Phyto-60-593.

Severe fire blight developed in the main trunk of eleven 5- to 6-year-old Magness pear trees with no visible symptoms elsewhere in the tree. In most infected trees, fire blight was first observed during fall and early winter. The earliest symptom was usually premature foliage coloration on a branch that originated at or near a trunk infection. The disease spread rapidly upward through the central leader and scaffold limbs, resulting in death of the trees. Artificial inoculation of succulent shoots of other 4-year-old Magness trees resulted in few light infections. However, injection of bacteria under the bark of 2-year-old branches of these trees killed three of four inoculated trees. It appears that the woody tissue of this variety is more susceptible to fire blight than its succulent shoots.