Fire Blight in the Geneva Apple Collection

Abstract

Ratings of the severity of fire blight (caused by Erwinia amylovora) were made on trees in the apple collection at the Geneva Experiment Station after severe epiphytotics in 1972 and 1974. The most severe rating for each cultivar, sport or numbered selection is reported on a total of 1224 clones on many of which fire blight has not been reported previously.

Based on natural infections, several authors (3, 4, 5, 6) have reported ratings of the susceptibility of many apple cultivars to Erwinia amylovora(Burrill) Winslow et al., the incitant of fire blight. Often the data were from 1-3 trees in one location (3,4,5). Aldwinckle (2) derived ratings based on a transcontinental survey of research and extension workers using many man-years of observations. However, only cultivars in substantial commercial production in the United States and Canada were listed (1). Shaw (5) reported the susceptibility of vegetative shoots of 25 apple cultivars to artificial inoculation in the greenhouse. These studies did not include cultivars and sports which were locally unavailable or were only recently produced.

This report summarizes observations of infections on 1224 cultivars, sports, numbered selections and Malusspecies. It does not, however, purport to unequivocally rate fire blight susceptibility. Fire blight has not prevously been reported on some of the clones observed. Many of the apples listed are presently unimportant commercially; some are unknown in North America but are important in other apple-growing regions.