Bacterial canker of stone‐fruits

SUMMARY On two different plots of cherry trees, the bacterial canker organism (Pseudomonas mors‐prunorum) outnumbered all other gram‐negative bacteria on the leaf surfaces in the approximate proportions of 4:1 and 3:1, respectively. The saprophytic flora was dominated by an organism having affinities with Erwinia spp. In mixed‐infection experiments this was shown to be capable of reducing the incidence and/or severity of leaf‐scar infection. The inhibitory activity of the saprophyte in different experiments was related to the amount of disease, and its general effect was similar to that which would have been expected from reducing the concentration of the pathogen in the inocula. Spraying bacterial suspensions on to trees substantially increased populations of the saprophyte, but these rapidly decayed and the natural equilibrium on the leaf surfaces was re‐established within a few days.