Genetic Diversity of Xanthomonas arboricola pv. juglandis (synonyms: X. campestris pv. juglandis;X. juglandis pv. juglandis) Strains from Different Geographical Areas shown by Repetitive Polymerase Chain Reaction Genomic Fingerprinting

Abstract

A world‐wide collection of 61 Xanthomonas arboricola pv. juglandis strains, isolated from Persian walnut (Juglans regia L.) or obtained from international culture collections and bacterial plant diseases laboratories, were studied by means of repetitive polymerase chain reaction (PCR) genomic fingerprinting using ERIC, BOX and REP primer sets and polyacrylamide gel electrophoresis. Cluster analyses were performed by UPGMA. Copper resistance, ability to hydrolize starch and quinate metabolism of the strains was also assessed. Pathogenicity was tested by inoculating leaves and nuts of Persian walnut seedlings. Polyacrylamide gel electrophoresis allowed very clear and reproducible differentiation of the PCR products. Cluster analysis showed the existence of three major groups of strains. The first two groups were 85% genetically similar, whereas the third clustered at 78% similarity with the other two. Each group could be divided into two subgroups which clustered according to the geographical origin of the isolates. In some cases, different genomic profiles were shown by strains from one country. This is possibly due to Persian walnut cultivation being mainly based on ecotypes and/or local seedlings that have become adapted to particular environments and so have allowed selection of different X.a. pv. juglandis populations. All strains were pathogenic and positive in starch hydrolysis and quinate metabolism tests. This is the first record of copper‐resistant strains occurring outside California, USA.