Characterization of Pseudomonas syringae Strains Associated with Shoot Blight of Raspberry and Blackberry in Serbia.

During May 2016, severe blight symptoms were observed in several raspberry and blackberry fields in Serbia. In total, 22 strains were isolated: 16 from symptomatic raspberry shoots, 2 from asymptomatic raspberry leaves, and 4 from symptomatic blackberry shoots. Additionally, eight raspberry strains, isolated earlier from two similar outbreaks, were included in the study. Pathogenicity of the strains was confirmed on detached raspberry and blackberry shoots by reproducing the symptoms of natural infection. The strains were Gram-negative, fluorescent on King's medium B, ice nucleation positive, and utilized glucose oxidatively. All strains were levan positive, oxidase negative, nonpectolytic, arginine dihydrolase negative, and induced hypersensitivity in tobacco leaves (LOPAT + - - - +, Pseudomonas group Ia). Furthermore, all strains liquefied gelatin and hydrolyzed aesculin but did not show tyrosinase activity or utilize tartrate (GATTa + + - -). Tentative identification using morphology, LOPAT, GATTa, and ice-nucleating ability tests suggested that isolated strains belong to Pseudomonas syringae. The syrB gene associated with syringomycin production was detected in all strains. DNA fingerprints with REP, ERIC, and BOX primers generated identical profiles for 29 strains, except for strain KBI 222, which showed a unique genomic fingerprint. In all, 9 of 10 selected strains exhibited identical sequences of four housekeeping genes: gyrB, rpoD, gapA, and gltA. Five nucleotide polymorphisms were found in strain KBI 222 at the rpoD gene locus only. In the phylogenetic tree based on a concatenated sequence of all four housekeeping genes, strains clustered within phylogroup 2 (i.e., genomospecies 1) of the P. syringae species complex, with pathotype strains of P. syringae pv. aceris and P. syringae pv. solidagae as their closest relatives. There was no correlation between genotype and geographic origin, particular outbreak, host, or cultivar.

Complete Genome Sequence of Xanthomonas campestris pv. campestris SB80, a Race 4 Strain Isolated from White Head Cabbage in Turkey.

Here, we report the complete genome sequence of the race 4 strain Xanthomonas campestris pv. campestris SB80, which was isolated from a symptomatic white head cabbage leaf in Samsun Province, Turkey, in 2019. The genome consists of a circular chromosome (5,129,762 bp) with a G+C content of 64.98%, for which 4,159 putative protein-coding genes, 2 rRNA operons, 54 tRNAs, and 86 noncoding RNAs (ncRNAs) were predicted.

First Report of Xanthomonas arboricola pv. pruni Causing Leaf and Fruit Spot on Apricot (Prunus armeniaca L.) in Montenegro.

In July 2020, symptoms of leaf and fruit spot were observed on two-year old apricot plants (Prunus armeniaca L.), cultivar Rubista in plantation covering approximately 0,5 ha near Podgorica, central Montenegro. The intensity of infection on leaves was more than 70%. Initially, leaf spots were mainly circular, 2 to 5 mm in diameter, water-soaked, surrounded by a weak chlorotic halo, but later became light to dark brown and necrotic. Eventually, the spots merged and necrotic tissue dropped out, leaving a "shot-hole" leaf appearance. On apricot fruits small, dark brown, mainly circular superficial lesions were observed. The lesions merged and formed large necrotic areas reducing the quality of fruits. Symptoms were not observed on woody parts, such as twigs or stem. A total of 10 bacterial strains, forming yellow, convex, and mucoid colonies on yeast extract-dextrose-CaCO3 (YDC) medium, were isolated from symptomatic leaf and fruit tissue. All strains induced hypersensitive reaction in tobacco leaves. They were Gram-negative, strictly aerobic, oxidase negative, catalase positive, hydrolyzed gelatine and esculin but not starch, and did not grow at 37°C, showing similar biochemical properties as a reference strain Xanthomonas arboricola pv. pruni (Xap) (NCPPB 416) used in all tests as a positive control. Strains were further identified by PCR analysis, using primer pair XapY17-F/XapY17-R (Pagani 2004; Pothier et al. 2011), resulting in a single band of 943 bp, characteristic for Xap. Additionally, BOX-PCR with the BOX A1R primer (Schaad et al. 2001) showed 100% homology in genetic profiles of all tested strains and control strain. Amplification and partial sequencing of the gyrB gene of four representative strains was performed using set of primers described by Parkinson et al. (2007). Obtained DNA sequences showed that analysed strains (GenBank nos. MW473770, MW473771, MW473772, and MW473773) share 99.44 to 99.57% of gyrB sequence identity with Xap pathotype strain ICMP51. Pathogenicity of all strains was confirmed by spraying young apricot shoots using a hand-held sprayer, and by infiltration of apricot leaves (cv. Roksana) from the abaxial surface using a syringe without needle, with the bacterial suspension (107 CFU/ml in sterile distilled water), in three replicates. Sterile distilled water and reference Xap strain (NCPPB 416), were used as negative and positive controls, respectively. The inoculated shoots and leaves were maintained at approx. 25°C and high humidity conditions. Tissue necrosis appeared on all inoculated shoots 5 to 11 days and leaves 5 to 9 days after inoculation. Koch's postulates were completed by re-isolation of the pathogen from inoculated tissue and identification by PCR using XapY17-F/XapY17-R primers. Based on pathogenic, biochemical and molecular characteristics, the strains isolated from apricot leaves and fruits in Montenegro were identified as Xap - causal agent of bacterial leaf spot and canker of stone fruits. This quarantine pathogen was previously reported on almond (Panic et al. 1998) and on peach (Popovic et al. 2020) in Montenegro. This is the first report of Xap affecting apricot in this country. Therefore, strict phytosanitary measures have to be implemented to prevent spread of the pathogen in other areas and other susceptible hosts.