SURVIVAL OF ERWINIA AMYLOVORA IN ASSOCIATION WITH MATURE APPLE FRUIT

Abstract

Mature fruit from naturally infected apple (Malus sylvestris Mill. ’Wealthy’) trees was free from a detectable population of Erwinia amylovora in the calyx, stem, peel and cortex. The pathogen failed to survive for 24 h on the surface of artificially inoculated fruit of Red and Golden Delicious apple in the orchard. In the laboratory, survival of the bacterium was excellent on the surface of apples when applied as natural ooze, or in a water suspension. Bacteria injected into the cortex of fruit of several cultivars survived as long as the apples were physiologically sound. Apples even from resistant cultivars developed symptoms of fireblight in storage. However, the absence of E. amylovora from symptomless fruit of naturally infected trees suggests that mature fruit presents a negligible risk for dissemination of fireblight bacteria.