Identification And Effect of Two Bacterial Contaminants on Apple Organogenesis

Shoots of the apple cultivar Golden Delicious clone B were maintained actively proliferating for several years and routinely used as source of leaves to regenerate adventitious shoots. Contamination appearing during proliferation did not affect the performances of axillary branching or shoot growth but was further related to a dramatic decrease of regenerative ability of the leaves. Two bacterial strains, C1 and C2, were isolated and identified on the basis of the 16S rRNA gene partial sequence analysis. C1 strain showed significant homology with Luteibacter, a gamma-proteobacterium isolated from the rhizosphere of Hordeum vulgare, while C2 showed the highest similarity with Staphylococcus pasteuri. Leaves artificially infected with either single C1 and C2 cells or both strains together recorded a significant drop in shoot regeneration ability and concealed the leaf morphogenic gradient. On the other hand, contaminated leaves produced more abundant callus that could result from the production of growth regulators by the bacterial strains.