Certain aspects of resistance of plum trees to bacterial canker: Part III. The action of cell‐free filtrates of Pseudomonas mors‐prunorum Wormald and related phyto‐pathogenic bacteria on plum trees

Abstract

A technique for introducing 2‐3 c.c. liquid into the bark of plum trees is described. Parallel injections with dyestuff throughout the spring failed to afford a reliable index of the invasive powers of the various test fluids introduced in this manner.A susceptible variety of plum (Giant Prune) showed greater injury by cell‐free filtrates of Ps. morsprunorum than did a resistant variety (Warwickshire Drooper), which showed negligible injury. The greatest injuries were caused by filtrates of cultures 5 weeks old, and over, especially when concentrated.Of other bacteria tested Ps. prunicola, Ps. syringae strains, Syringa 3, Ap. No. 1, Ap. No. 2, and Bact. pruni, yielded damaging filtrates, whereas Ps. syringae, strains pear 6 and 7, Ps. tabaci, Ps. fluorescens, Ps. marginalis, Ps. phaseolicola, Ps. tumefaciens, Ps. pisi and Ps. cerasi failed to do so.Some evidence is advanced for the view that the deleterious activity of Ps. mors‐prunorum may be due in part to an endotoxin of protein nature obtainable from the dried bacterial cells by acetic acid extraction.