Since the summer of 2000, vertical oozing cankers have been observed on trunks and branches of Persian walnut trees (Juglans regia). Cvs. Fernor, Chandler, Mayette, and Hartley were the most frequently affected, but cvs. Lara and Franquette could also be affected. Brenneria nigrifluens (synonym Erwinia nigrifluens) (3) was isolated from diseased trees from 13 orchards and nurseries in southwestern (Aquitaine, Périgord, Charentes, and Quercy), southeastern (Grenoble areas), and western (near Angers) France. Cankers were observed on trunks and branches where brown-to-black exudates staining the bark appeared mainly in the summer. Isolations were performed primarily from exudates but also from infected tissues by using King's medium B. Colonies similar in appearance to Brenneria nigrifluens (1) were purified and characterized. Gram reaction, Kovac's oxidase, oxidative-fermentative metabolism, and urease activity were assayed for all isolates. API Biotype 100 kits (BioMérieux, Marcy l'Etoile, France) were used as recommended, except that incubations were at 28°C for 4 days. When compared with the reference strain (French Collection of Plant Pathogenic Bacteria (CFBP) 4998T = National Collection of Plant Pathogenic Bacteria (NCPPB) 564T = American Type Culture Collection (ATCC) 13028T) from California, 14 isolated strains were identified as B. nigrifluens on the basis of physiological and biochemical characteristics. These 14 strains were deposited in the CFBP under Accession Nos. 6746 to 6759. Pathogenicity of three selected strains (CFBP 6746, 6747, and 6758) was confirmed by inoculating branches of 7-year-old walnut trees with 108 CFU of each isolate introduced in wounds (2). The reference strain (CFBP 4998T) and water were similarly inoculated as controls. Two and five months later, necrotic lesions were observed in the inner bark and dark lines were observed in internal wood, but no external cankers were observed on any trees inoculated with the local and reference strains. B. nigrifluens was reisolated from the dark lines in internal wood up to approximately 10 cm from the inoculation site. To our knowledge, this is the first report of this bacterium in France. References: (1) L. Hauben et al. Syst. Appl. Microbiol. 21:384, 1998. (2) M. Ridé and S. Ridé. Proc. Int. Conf. Plant Pathogenic Bacteria, 4th, 2:957, 1978. (3) E. E. Wilson et al. Phytopathology 47:669, 1957.

Currently, bacterial canker caused by Pseudomonas syringae is a major cause of dieback and tree death in wild cherry (Prunus avium) plantations. The evaluation of breeding collections is needed to produce less susceptible clones or cultivars. Resistance tests were performed using excised shoots (1 and 2 years old) from 79 clones in the laboratory. A subset of 10 clones was also tested in the field. The clones were inoculated with four to seven isolates of a set of 15 isolates of P. s. pv. morsprunorum, P. s. pv. syringae, P. s. pv. persicae, P. syringae pv. avii and P. fluorescens. In the laboratory tests, older and larger shoots were more susceptible. In the field test, size and age of the shoots were not related to girdling by the bacterial canker. Two-year-old shoots were best for clonal discrimination. Correlations between 1 and 2-year-old shoots were significant but not high. The isolates varied a lot between experiments, but as the clone · isolate interactions were always low, breeding could thus be facilitated. The ranking of clones was conserved quite well between two laboratory tests, but not between two others. Good agreement was found for the best clones in the laboratory tests and in the field test. However, the two worst clones in the latter were among the best in one laboratory test. At least two independent tests in the laboratory are needed to evaluate resistance/susceptibility of clones. Broad sense heritability for resistance varied from 0.27 to 0.51. Although moderate, such heritability clearly encourages a breeding approach to reduce the problem of bacterial canker.

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