Relationship of Erwinia herbicola to Erwinia amylovora

Abstract

A yellow bacterium which had inhibited Erwinia amylovora was identified as Erwinia herbicola. Erwinia herbicola occurred on leaf surfaces in large numbers on apple, cherry, and apricot trees, but in small numbers on pear leaves. It was not pathogenic, but was a secondary invader of diseased tissues. Fire blight branch cankers were examined for occurrence and location of E. amylovora and E. herbicola. Erwinia herbicola occurred mixed with E. amylovora. Both bacteria were isolated at maximum frequency about 7.6 cm above the edge of downward advancing cankers.Partial control of fire blight was obtained in the greenhouse and field plots by inoculation of pear blossoms with E. herbicola 24 h before inoculation with a virulent suspension of E. amylovora. The inhibitory effect could occur in pear blossom nectar. On media containing sugar concentrations comparable to pear nectar, E. herbicola consumed all organic nitrogen in the medium and reduced the pH to a level inhibitory to E. amylovora.