In nature there are species containing homologs of T-DNA genes of agrobacteria (сT-DNA) in their genomes. Such plants are called naturally transgenic ones. Interaction with the microbiota is one of the possible functions of cT-DNA, discussed in the literature. Linaria plants are the most suitable for the investigation of the probable ecological role of T-DNA, since they widely spread. The first stage in the evaluation of plant-microbial interactions involving these plants is the description of isolates with contrasting virulence for toadflax. The search and DNA-barcoding of such isolates of Phoma-like fungi was the goal of this work. 14 strains isolated from the plants of the families Plantaginaceae and Scrophullariaceae were analyzed. The of multilocus analysis included amplification and sequencing of internal transcribed spacers, a large subunit of RNA, a tubulin gene. Based on molecular data, 9 strains were assigned to the species Boeremia exigua, which has a wide range of habitats and a wide specialization. Strains of this species were virulent against L. vulgaris, but differed in aggressiveness with respect to this plant. Thus, a collection of strains was characterized, which can later be used for a more detailed study of the immune response of the naturally-transgenic L. vulgaris plant in response to inoculation with the B. exigua phytopathogen. As a result of the work, we identified the narrow host range fungi Heterophoma novae-verbascicola, and broad host range pathogens Plectosphaerella cucumerina, Phoma herbarum and trichothecium roseum. Among them, only P. cucumerina was a weak pathogen of L. vulgaris. These results confirm the early data on the depleted mycobiota of L. vulgaris.