AN INSIGHT IN SOME POPULATION FEATURES OF XANTHOMONAS ARBORICOLA pv. JUGLANDIS

Xanthomonas arboricola pv. juglandis (Xaj) is the causal agent
of bacterial blight of walnut, an emerging disease, which has the
potential to severely affect walnut orchards. An Italian strain collection
of Xaj, obtained during the past 3 years from affected orchards
in Romagna, was first assayed with conventional PCR with
XajF/XajR primer pair developed to confirm strain identity. The
population structure of the collection of Xaj isolates, confirms the
presence of different genetic groups identified by rep-PCR (using Italian collection are currently being analysed by MLSA (multi
locus sequence analysis), using 7 primers for 7 different housekeeping
genes, with the purpose to better characterise the Italian
isolates for phylotyping. The study of copper resistance on a wide
collection of over 150 Xaj strains frequently showed high resistance
(up to 500 ppm Cu++): two strains have been further studied
confirming the presence of chromosomal genes copA and copB involved
in the general copABCD copper resistance structure, as
described for Pseudomonas syringae. Sequencing and comparing
with other Xanthomonads were done. The elucidation of Xaj
population structure may help to deeper investigate some additional
aspects of the molecular epidemiology of the disease, thus
allowing a better control strategy in the field.
the REP, BOX and ERIC primers) and by multilocus sequence
typing (MLST) and multilocus variable number analysis of tandem
repeat (MLVA). Xaj and Xaj-like bacterial isolates from the