EVALUATION OF THE EFFICIENCY OF A CONVENTIONAL PCR PROTOCOL FOR THE DIAGNOSIS OF BACTERIAL SPOT DISEASE CAUSED BY XANTHOMONAS ARBORICOLA pv. PRUNI IN STONE FRUITS AND ALMOND

Xanthomonas arboricola pv. pruni (Xap), the causal agent of bacterial spot disease of stone fruits and almond, has a quarantine status for the European Union and the European and Mediterranean Plant Protection Organization. The symptoms in the diverse hosts show some differences and, although being quite typical, could be confused with those of some fungal diseases or other biotic or abiotic causes. Consequently, an accurate molecular diagnosis method is required for a rapid identification of the pathogen in samples of imported plants, from nurseries, orchards, etc. A protocol for conventional PCR designed by Pagani (2004) has been the only molecular analytic tool available for several years. It has been optimised for improving its specificity and sensitivity, and the results of its evaluation in 316 bacterial spot-like symptomatic samples of almond, apricot, cherry, Japanese plum and peach, compared with those of isolation and real-time PCR, are reported. The optimised PCR protocol showed specificity for a collection of Xap strains tested. Few non-desired reactions were obtained with some other xanthomonads which have not been reported from Prunus species. Sensitivity thresholds ranged from 102 to 105 CFU ml-1, depending on the hosts and type of plant material. This conventional PCR assay proved to be an excellent candidate for a rapid screening and presumptive diagnosis in cases where real-time PCR equipment is not available.