Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Erwinia alni, a new species causing bark cankers of alder (Alnus Miller) species.

Abstract

The causal agent of an undetermined disease of black alder (A. glutinosa) and Italian alder (A. cordata) was identified as an Erwinia species. The bacterium induced dark brown necrotic cankers on alder plants; these were often longitudinally elongated and occurred in the bark of the trunks and also in the bark of branches, twigs and suckers. A dark watery liquid exuded from small cracks in the cankers and stained the bark surface. Disease symptoms were produced on the trunks of 2-year-old black and Italian alder trees after artificial inoculation of selected strains of bacteria obtained from typical bark cankers. Morphological examination of the pathogen by EM showed that it was a motile rod-shaped organism. All of the strains examined were Gram negative, oxidase negative and facultatively anaerobic with fermentative metabolism and had the general characteristics and fatty acids of members of the family Enterobacteriaceae. Strains PVFi 20T (T=type strain), PVFi 23, PVFi 25 and PVFi 27 were chosen for further characterization. These 4 strains exhibited 96 to 100% DNA homology in hybridization experiments performed at 40 and 50°C. They were most closely related to E. nigrifluens (levels of homology 40°, 49 to 65%). Phenotypic differentiation from E. nigrifluens, which induces a similar disease on Persian walnut but is nonpathogenic on alder, is based on positive reactions by the alder strains for acetoin (Voges-Proskauer reaction), endoglucanase activity and acid production from maltose and negative reactions for esculin hydrolysis and acid production from raffinose, melibiose, sorbitol and inositol. The fatty acid profiles of the alder strains were quantitatively different from those of all previously validly named plant-pathogenic species belonging to the Enterobacteriaceae. On the basis of data described above, the name E. alni is proposed for the new organism.