VIEW ARTICLE

Physiology and Biochemistry

Diversity of the Fire Blight Pathogen in Production of Dihydrophenylalanine, a Virulence Factor of Some Erwinia amylovora Strains. Thomas Schwartz, Max-Planck-Institut für medizinische Forschung, Jahnstr. 29, D-6900 Heidelberg, Federal Republic of Germany; Frank Bernhard, Richard Theiler, and Klaus Geider. Max-Planck-Institut für medizinische Forschung, Jahnstr. 29, D-6900 Heidelberg, Federal Republic of Germany. Phytopathology 81:873-878. Accepted for publication 13 February 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-873.

Various Erwinia amylovora strains from different origins were assayed for phytotoxin production. When cultivated pear cells were embedded in solidified plant medium and inoculated with bacteria, a zone of growth inhibition was observed for some of the strains. A membrane-diffusible toxic compound was identified as l-2,5-dihydrophenylalanine (DHP), an inhibitor of the shikimic acid pathway. In plants DHP caused a reduction of elicitor-induced synthesis of phytoalexins and killed cultivated pear cells within 1 day. Bacterial synthesis of DHP was prevented by aromatic amino acids in the growth medium and was increased when pear juice or malate was present. Pear cells also were killed by strains that did not produce DHP, indicating a second plant cell-damaging pathway.