Xanthomonas euvesicatoria phage KΦ1, a member of Myoviridae family, was isolated from the rhizosphere of pepper plants showing symptoms of bacterial spot. The phage strain expressed antibacterial activity to all X. euvesicatoria strains tested and did not lyse other Xanthomonas spp., nor other less related bacterial species. The genome of KΦ1 is double-stranded DNA of 46.077 bp including 66 open reading frames and an average GC content of 62.9%, representing the first complete genome sequence published for a phage infecting xanthomonads associated with pepper or tomato. The highest genome similarity was observed between phage KΦ1 and the Xanthomonas oryzae pv. oryzae specific phage OP2. On the other hand, when compared with other members of the genus Bcep78virus, the genome similarity was lower. Forty-four (67%) predicted KΦ1 proteins shared homology with Xanthomonas phage OP2, while 20 genes (30%) were unique to KΦ1. Phage KΦ1, which is chloroform resistant and stable in different media and in the pH range 5-11, showed a high titer storage ability for at least 2 years at +4°C. Copper-hydroxide and copper-oxychloride reduced phage activity proportionally to the used concentrations and the exposure time. UV light was detrimental to the phage strain, but skim milk plus sucrose formulation extended its survival in vitro. The phages survived for at least 7 days on the surface of pepper leaves in the greenhouse, showing the ability to persist on the plant tissue without the presence of the host bacterium. Results of three repeated experiments showed that foliar applications of the unformulated KΦ1 phage suspension effectively controlled pepper bacterial spot compared to the standard treatment and the untreated control. The integration of the phage KΦ1 and copper-hydroxide treatments resulted in an increased efficacy compared to the copper-hydroxide alone.

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Xanthomonads, members of the family Xanthomonadaceae, are economically important plant pathogenic bacteria responsible for infections of over 400 plant species. Bacteriophage-based biopesticides can provide an environmentally friendly, effective solution to control these bacteria. Bacteriophage-based biocontrol has important advantages over chemical pesticides, and treatment with these biopesticides is a minor intervention into the microflora. However, bacteriophages’ agricultural application has limitations rooted in these viruses’ biological properties as active substances. These disadvantageous features, together with the complicated registration process of bacteriophage-based biopesticides, means that there are few products available on the market. This review summarizes our knowledge of the Xanthomonas-host plant and bacteriophage-host bacterium interaction’s possible influence on bacteriophage-based biocontrol strategies and provides examples of greenhouse and field trials and products readily available in the EU and the USA. It also details the most important advantages and limitations of the agricultural application of bacteriophages. This paper also investigates the legal background and industrial property right issues of bacteriophage-based biopesticides. When appropriately applied, bacteriophages can provide a promising tool against xanthomonads, a possibility that is untapped. Information presented in this review aims to explore the potential of bacteriophage-based biopesticides in the control of xanthomonads in the future.

SuMMARyDue to an overlapping host range, similar symptomatology and many common characteristics, Pseudomonas syringae pathovars originating from stone fruits can easily be misidentified. In order to select tests for rapid and efficient differentiation of P. s. pvs. syringae, morsprunorum and persicae, we studied the suitability and differentiating potential of some standard bacteriological and molecular methods. Differentiation of the strains was performed using LOPAT, GATTa and ice nucleation tests, nutrient sucrose broth growth and utilization of various carbon sources. PCR method enabled the detection of toxin-producing genes: syrB and syrD in P. s. pv. syringae, and cfl gene in P. s. pv. morsprunorum race 1. Syringomycin production by pv. syringae was confirmed in bioassay using Geotrichum candidum, Saccharomyces cerevisiae and Rhodotorula pilimanae as indicator organisms. Pathogenicity test on lemon and immature nectarine fruits, as well as on string bean pods, showed different intensity of reaction of the inoculated material which could separate pv. syringae from the other two pathovars. PCR-based repetitive sequences, Rep-PCR with REP, ERIC and BOX primers revealed different genetic profiles within P. syringae pathovars.

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