## 3 Materials and Methods
### Analysis of Volatile Compounds (HS-SPME-GC)  
Volatile compounds were analyzed using an Agilent 7890A chromatograph (Agilent Technologies, Santa Clara, CA, USA) coupled to a mass spectrometer Agilent MSD 5975C  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Strains** & **Origin** \\ \hline _Alternaria alternata_ & LOCK 408 & Collection of Pure Cultures of Industrial Microorganisms LOCK at the Lodz University of Technology (Lodz, Poland) \\ \hline _Fusarium oxysporum_ & Z154 & Plant Breeding and acclimatization Institute (IHAR)—National Research Institute (Radzików, Poland) \\ \hline _Pectobacterium carotovorum_ & PCM 2056 \({}^{\star}\) & Polish Collection of Microorganisms of the Hirszfeld Institute of Immunology and Experimental Therapy of the Polish Academy of Sciences (Wroclaw, Poland) \\ \hline _Alternaria tenuissima_ & DSM 63360 & \\ _Fusarium sambucinum_ & DSM 62397 & \\ _Rhizoctonia solani_ & DSM 22843 & German Collection of Microorganisms and Cell Cultures GmbH \\ _Colletotrichum cococodes_ & DSM 62126 & (DSMZ, Braunschweig, Germany) \\ _Phoma exiqua_ & DSM 62040 & \\ _Streptomyces scabiei_ & DSM 4077 \({}^{\star}\) & \\ \hline \hline \end{tabular} \({}^{\star}\)bacteria.  
\end{table}
Table 5: Potato pathogens used in the study.  
(Agilent Technologies, Santa Clara, CA, USA). A capillary column DB-1 ms 60 m \(\times\) 0.25 mm \(\times\) 0.25 \(\upmu\)m (Agilent Technologies Santa Clara, CA, USA) was applied to separate the compounds. For extraction of volatile compounds, the solid-phase microextraction technique was used. Adsorption was carried out by using the fiber covered with 50/30 \(\upmu\)m Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS) phase (length 1 cm).  
The glass vessel with potatoes (i.e., control samples, as well as contaminated samples before and after 14-day storage), was tightly covered with a lid containing a sampling port and then incubated at 20 \({}^{\circ}\)C for 30 min. During this time the vessel was saturated with volatile compounds from potato tubers. Next, the SPME fiber was inserted into the headspace of the vessel via the sampling port, followed by the exposure for 60 min at 20 \({}^{\circ}\)C. After adsorption of volatiles from the headspace, the fiber was retracted into the needle and transferred to the inlet of the GC apparatus for desorption of volatile analytes. Desorption was carried out for 5 min at 250 \({}^{\circ}\)C. For fiber cleaning before each extraction, the fiber was heated for 10 min in the inlet of the GC apparatus, at 260 \({}^{\circ}\)C.  
All injections were performed in a splitless mode. As a carrier gas, helium was used with a flow rate of 1.1 mL/min. The GC oven temperature was programmed to increase from 30 \({}^{\circ}\)C (10 min) to 70 \({}^{\circ}\)C at a rate of 5 \({}^{\circ}\)C/min and kept for 1 min, then to 230 \({}^{\circ}\)C at a rate of 10 \({}^{\circ}\)C/min, and finally kept for 2 min. The temperatures of the MS ion source, transfer line, and quadrupole analyzer were 230, 250, and 150 \({}^{\circ}\)C, respectively. The electron impact energy was set at 70 eV. The mass spectrometer was operating in the full scan mode. Qualification of volatile compounds was performed by comparison of obtained spectra with the reference mass spectra from NIST/EPA/NIH mass spectra library (2012; Version 2.0 g.) and confirmed with the use of the deconvolution procedure. Moreover, retention indices (RI) were calculated according to the formula proposed by [PERSON] and [PERSON] [73] relative to a homologous series of n-alkanes from C5 to C23. Retention indices were compared with reference compounds and literature data [74; 75]. Data processing was conducted with Mass Hunter Workstation Software (Agilent, Santa Clara, CA, USA). The control sample as well as infected samples were prepared in duplicate.