## 2 Materials and Methods
### Isolating and Identifying the Fungi from the Roots Infected Internally  
The main roots of horseradish with visible internal discoloration of the vascular bundles were included in the mycological analysis. The material for isolation was collected immediately after health assessment. In accordance with the adopted phytopathological procedure, 30 roots with the strongest symptoms of Verticillium wilt of horseradish roots and with even thickness (diameter approx. 2 cm) were taken from each combination. The root was cut lengthwise, and then one 1-milimeter-thick half-slice (disc) was cut transversely, thus obtaining a total of 60 half-discs. Sections 2 and 3 mm in size were cut from the border of healthy and diseased tissue. From each combination of sections, 200 were prepared, which weighed 5 g. Then, they were disinfected for 30 s in 0.5% sodium hypochlorite (Javal, Warszawa, Poland). The root fragments were rinsed three times for 10 min in sterile distilled water and thoroughly dried on sterile gauze. Then, 10 pieces at a time, they were placed on solidified PDA (potato dextrose agar) medium with 0.05 g:1-chloramphenicol and pH 6.5 in Petri dishes with a diameter of 150 mm. The fungi were grown in an air-conditioned chamber for up to 10 days, at a temperature of 23 \({}^{\circ}\)C and a 12-h light cycle. The number of obtained isolates was counted, which corresponded to the number of colony forming units (CFU) per 5 g of diseased horseradish roots. The fungal cultures were transported onto PDA and water agar (WA) medium. The filamentous fungi were identified using the MALDI-TOF MS technique (matrix assisted laser desorption/ionization time-of-flight mass spectrometry), which uses mass spectroscopy to determine ribosome protein profiles. Reference spectra for these are stored in the library database of Bruker Daltonik GmbH [56].  
The cultivation and sample preparation of the filamentous fungi was performed according to the standard operating procedure developed by BrukerDaltonik GmbH. Tubes of 8 mL Modified Fluid Medium cat. no. 221014 (Becton Dickinson) were inoculated with a small amount of three-day-old fungal hyphae and sealed with a lid. They were then placed in an SB2 rotator (cat. no. Y552, Carl Roth GmbH & Co KG) and incubated in the top mix until sufficient biological material was acquired. A detailed methodology for obtaining supernatants (crude protein extract) from the fungi is presented in the work of [PERSON] et al. [42].  
Then, 1 mL of supernatant was pipetted onto a steel MALDI plate and allowed to dry at room temperature. Subsequently, 1 mL of the alpha-cyano-4-hydroxycinnamic acid solution--HCCA matrix (cat. no. 8255344)--was applied and allowed to dry at room temperature. The plate was inserted into a MALDI Biotyper microflex apparatus, linked via computer to a database of reference spectra for fungi contained in Filamentous Fungi Library 1.0 (BrukerDaltonik GmbH). The spot on the plate where the strains had beenlocated was marked, given a number, and the identification was started via the \"start\" table. Fungi identification was conducted using MBT Compass research use only (RUO) 4.1.60 software. Each isolate was identified twice.