Genetic diversity of Xanthomonas arboricola strains isolated from symptomatic hazelnuts in Chile

The bacterial blight of Corylus avellanae, caused by Xanthomonas arboricola pv. corylina (Xac), induces severe yield losses in all the regions of its intensive cultivation around the world. The aim of this study was to assess the genetic diversity among 60 Xanthomonas-like strains isolated from symptomatic tissues of hazelnut cvs. Barcelona and Tonda di Giffoni in six Chilean regions during the period 2016-2018. These isolates were identified through molecular analyses. The evaluation of genetic diversity was then carried out by Rep-PCR (BOX-, ERIC- and REP-PCR) analysis. The genetic profiles were transformed into a binary matrix in order to perform the phylogenetic analysis and the dendrogram construction (by using UPGMA cluster analysis and Jaccard similarity index). In addition, the same profiles were analyzed by the BioNumerics v.7.6. software using the Xac strain NCPPB935 as reference and the X. axonopodis pv. vitians DISTAL9081 as out-group strain. Selected isolates were then subjected to the pathogenicity test on highly susceptible hazelnut cultivars. Among the 60 isolates, 19 were identified as X. arboricola (Xa) and 20 as Xac strains, whereas 21 isolates resulted Xa- and Xac-negative. The 39 Xac strains were differentiated in 5-6 genetic groups at approx. 50-60% similarity level by the BioNumerics elaboration, whereas the elaboration of the binary matrix of concatenated profiles allowed their separation in 7 genetic groups at approx. 60-70% similarity level. No relationships were found between amplification pattern, the plant organ of isolation, or the geographical origin of the isolates with the similarity groups delineated by the bioinformatics analyses.