# Characteristic of _Pseudomonas syringae_ pv. _atrofaciens_ Isolated from Weeds of Wheat Field
## 4 Discussion  
Considering the significant number of weeds in the Ukrainian wheat fields and the ability of weeds to serve as an ecological niche for bacterial pathogens, weeds in wheat crops were collected from symptomatic samples. As a result of the work, seven isolates of _P. syringae_ from _S. aureus_is and _P. argemone_ grew in wheat crops and were isolated. Further identification of the isolates with the determination of their affiliation to the particular pathway was difficult due to the high affinity of _P. syringae_ patovars for biochemical, physiological, and even genetic features [10; 24; 25; 26]. The pahovar of the species _P. syringae_ is usually determined by the host plant. It should be noted that the status of such a taxonomic unit as pahovar within the species _P. syringae_ is actively discussed in the scientific literature [24; 27; 28]. Some researchers consider the division into pathways unjustified [10; 24; 27; 29] and claim that _P. syringae_ is a universal pathogen. However, other studies have shown the possibility of differentiating pathovar for pathogenic properties and some other biological characteristics [24; 30; 31; 32]. When verifying the virulence properties, these seven isolates' ability to cause disease to both weeds (_S. aureus_is and _P. argemone_) and wheat was confirmed. After artificial infection of wheat, light brown spots with a dark border were formed, which eventually increased in size and covered the stem, leading to a darkening of the stem core. Such symptoms are characteristic of the causative agent of the basal glume rot of wheat [6]. Analyzing the results of serological studies of the causative agent of the basal glume rot of wheat, we concluded that the strains of _P. syringae_ isolated from different crops and weeds were similar in antigenic composition and belonged to serogroups II, IV, V, or VI [19]. The host plant determines the prevalence of specific serogroups and, in our opinion, is possibly associated with the best survival of the strains of these serogroups in various conditions. This hypothesis is supported by the evidence that many strains usually represent these serogroups. The fact that most of the strains isolated from weeds were assigned to the serogroups II and IV according to the results of agar precipitation indicates the predominance of these serogroups among pathogens isolated from wheat also among pathogens isolated from other plant species. Figure 5: Cluster analysis of RAPD patterns obtained with primer OPA-13 of _Pseudomonas syringae_ strains (Jaccard distance, the nearest neighbor clusterization method). All studied bacterial strains, regardless of the source of their isolation, are similar in the qualitative composition of fatty acids, and all strains contain hydroxy fatty acids, which are important for confirming their belonging to _P. syringae_[33]. The presence of differences in the spectrum of fatty acids is a feature of each strain and does not correlate with differentiation into pathways [33]. The results of the fatty acid composition of _P. syringae_ cell lipids are consistent with the literature: most of the hydroxy acids in _P. syringae_ are present in the amount at less than 5% of the total peak area. [PERSON] et al. [33] established the possibility of using fatty acid composition analysis to identify phytopathogenic bacteria at the species level. The RAPD-PCR method with primer OPA-13 (5\({}^{\prime}\)-CAGCASSACAC-3\({}^{\prime}\)) was successfully used by other researchers for the genetic analysis of _P. syringae_[25; 34] and to analyze the genetic heterogeneity of the wheat pathogen population in Ukraine [23]. RAPD-PCR is a useful technique for studying the genetic relationship between bacterial strains due to specificity and sensitivity. Analysis of literature data [21; 25] and our previous studies have shown that OPA-13 is the most optimal primer for identifying _P. syringae_ pv. _atrofaciens_ strains isolated from wheat crops.