ERWINIA ALNI, A NEW SPECIES CAUSING BARK CANKERS OF ALDER (ALNUS MILLER) SPECIES

The causal agent of an undetermined disease of black alder (Alnus glut inosa) and Italian alder (Alnus cordata) was identified as an Erwinia species, This alder bacterium induces dark brown necrotic cankers on a lder plants; these cankers are often longitudinally elongated and occu r in the bark of the trunks and also in the bark of branches, twigs, a nd suckers, A dark watery liquid often exudes from small cracks in the cankers and stains the bark surface, Disease symptoms were produced o n the trunks of 2-year-old black and Italian alder trees after artific ial inoculation of selected strains of bacteria obtained from typical bark cankers (G, Surico and L, Mugnai, Tnf, tore Fitopatol. 12:41-43, 1992), Morphological examination of the pathogen by electron microscop y showed that it is a motile rod-shaped organism, All of the strains e xamined were gram negative, oxidase negative, and facultatively anaero bic with fermentative metabolism and had the general characteristics a nd fatty acids of members of the family Enterobacteriaceae. Strains PV Fi 20(T) (T = type strain), PVFi 23 PVFi 25, and PVFi 27 were chosen f or further characterization. These four strains exhibited 96 to 100% D NA homology in hybridization experiments performed at 40 and 50 degree s C, They were most closely related to Erwinia nigrifluens (levels of homology 40 degrees C, 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 st rains for acetoin (Voges-Proskauer reaction), endoglucanase activity, and acid production from maltose and negative reactions for esculin hy drolysis and acid production from raffinose, melibiose, sorbitol, and inositol, The fatty acid profiles of the alder strains were quantitati vely different from those of all previously validly named plant-pathog enic species belonging to the Enterobacteriaceae, On the basis of data described above, the name Erwinia alni is proposed for the new organi sm.