INVESTIGATION OF FIRE-BLIGHT OF PEAR IN ENGLAND

Outbreaks of fire-blight, caused by Erwinia amylovora, in Kentish orchards during 1957 constitute the first authenticated record of the disease in Europe. The origin of the disease is unknown, but evidence suggests that it was not present in the orchards prior to 1957. The seasonal development and symptoms of the disease are described in detail. Fire-blight attacked trees only during the growing season; infection began in the blossoms, particularly summer blossoms, and spread into the branches forming cankers, in many of which the pathogen remained viable during the winter 1957-8. In the orchards examined there was a higher incidence of new infections by July 1958 on trees attacked the previous year than on those which were then healthy, and this is discussed in relation to overwintering sources of inoculum. The distribution of the disease in orchards during 1957 and 1958 was consistent with spread by pollinating insects rather than rain. The outstanding susceptibility of the variety Laxton's Superb in all localities was attributed partly to its tendency to produce abundant secondary blossom. Inoculations of blossoms, fruits, shoots and branches showed it also to have less inherent resistance than the varieties Williams's Bon Chretien and Conference, neither of which has been seriously affected in the field. The progress of symptoms following inoculation of pear and infection experiments with apple, Cotoneaster sp., Pyracantha sp., and other hosts, are described. A comparison of climatic conditions favouring the disease in the U.S.A., i.e. high temperatures and high humidity, with meteorological records at East Mailing, suggests that epidemic infection of spring blossom would be exceptional in this country.