Implementation of IPM strategies to control bacterial diseases of stone fruits and nuts caused by copper resistant/ tolerant pseudomonads and xanthomonads

Bacterial canker of stone fruits caused by Pseudomonas syringae pv. syringae and Pseudomonas syringae pv. morsprunorum, and bacterial blight of walnut caused by Xanthomonas arboricola pv. juglandis, have been studied for over a century and have resulted in significant advances in our understanding of the epidemiology of foliar bacterial diseases and epiphytic life cycle of these pathogens. Recent studies on the ecology, characterization, and identification of pathogens have been prompted by the economic importance of the diseases and the lack of effective control measures. A collection of 54 P. syringae spp. on apricot and 47 X. a.pv. juglandis strains on walnut were studied using repetitive polymerase chain reaction (PCR) genomic fingerprinting using ERIC, BOX, and REP primer sets, and Multi-Locus Sequence Analysis (MLSA). Copper tolerance of all strains were assessed by observing bacterial growth on copper sulphate-added media, and the results were compared to those of a five-year-old study in the same area. This thesis showed that the frequency of copper resistant bacteria increased after repeated treatments with copper-based compounds. These findings suggest that the selection of copper-resistant strains may be a major cause of control failures after copper bactericide treatment. Bacteriophages, as realistic and environmentally friendly microorganisms, could be a viable option for controlling these bacterial diseases. In this thesis, ten novel phages that lyse P. s. pv. syringae and ten novel phages that lyse X. a. pv. juglandis were isolated from apricot and walnut fruits, leaves, soil, and irrigation water in Northern Italy. The restriction endonuclease digestion of phages revealed that there are three distinct phage groups, designated as groups 1, 2, and 3. In laboratory tests, all phages had a promising lytic effect on P. s. pv. syringae and X. a. pv. juglandis. P. s. pv. syringae and X. a. pv. juglandis showed promising lytic effect in laboratory trials.