# Inactivation of the Plant Pathogen _Pythium ultimum_ by Plasma-Processed Air (PPA)
## 3 Results  
Non-treated _P. ultimum_ on PDA agar blocks (positive control, no PPA) displayed a logistic radial growth of mycelia within the course of 14 days (Figures 1 and 2). Exponentialgrowth occurred from day one to day five with an increase in mean mycelia diameter of 16 mm (Figures 1 and 2). Slower growth reaching stationary phase was detected from day six to day fourteen, which resulted in an increase to a final maximum mean diameter of 28.2 mm.  
Gas controls were applied to exclude any dry-out effects of Pythium on agar blocks. However, similar growth patterns were recorded for the gas controls without PPA (Figures 1 and 2) compared to untreated controls; no statistically significant differences were detected for growth of untreated and gas controls (Table 1). Using the gas flow of 63 slm, exponential growth in the gas control was detected from day one to day five with an increase in mean mycelium diameter of 15.9 mm (Figures 1 and 2). Similar to the untreated controls, slower growth was observed from day six reaching a maximum mean diameter of 28.6 mm at day fourteen. For 73 slm gas flow control, the exponential growth phase extended till day six reaching a mean diameter of 16.3 mm. Logistic growth occurred from day seven till day fourteen resulting in a maximum mean diameter of 28.5 mm.  
Figure 1: Radial growth of _Pythium_ mycelia on PDA agar plates over 14 days of incubation. One representative replicate of seven replicates per run is displayed. All seven replicates per treatment showed similar results. PC: positive control, inoculated no PPA, two controls using gas flow of air only without microwave torch ignition (i.e., gas) and three different PPA treatment modes. For scaling classification note that petri dishes are 85 mm in diameter.  
All PPA treatments, irrespective of applied gas flow rate or exposure time, resulted in 100% inactivation of _P. ultimum_ on PDA agar. No detectable mycelial growth was observed over the entire 14 days of incubation (Figures 1 and 2). This resulted in significantly lower radial growth for PPA treatments relative to both the control groups (Table 1).  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Source** & **DF** & \multicolumn{2}{c}{**Type III Sum of Squares**} & **Mean Square** & **F** & \(p\) \\ \hline Treatment & 3 & 1461.292 & 1782.411 & 78.987 & \textless{}0.001 \\ \hline
**Comparison** & **Diff. of means** & **t** & \(p\)** & & \\ \hline PC vs. 63 slm, 25 min/PPA & 20.533 & 11.436 & \textless{}0.001 & & \\ PC vs. 73 slm, 15 min/PPA & 20.533 & 11.436 & \textless{}0.001 & & \\ PC vs. 73 slm, 10 min/PPA & 20.533 & 11.436 & \textless{}0.001 & & \\ PC vs. 63 slm, gas only & 0.136 & 0.0756 & 1 & \\ PC vs. 73 slm gas only & 0.0702 & 0.0391 & 1 & \\
63 slm gas only vs. 63 slm, 25 min/PPA & 20.669 & 11.511 & \textless{}0.001 & \\
63 slm gas only vs. PPA 73 slm, 15 min/PPA & 20.669 & 11.511 & \textless{}0.001 & \\
63 slm gas only vs. PPA 73 slm, 10 min/PPA & 20.669 & 11.511 & \textless{}0.001 & \\
73 slm gas only vs. 63 slm, 25 min/PPA & 20.599 & 11.472 & \textless{}0.001 & \\
73 slm gas only vs. 73 slm, 10 min/PPA & 20.599 & 11.472 & \textless{}0.001 & \\
73 slm gas only vs. 63 slm gas only & 0.0702 & 0.0391 & 1 & \\
63 slm, 25 min/PPA vs. 73 slm, 15 min/PPA & 0 & 0 & 1 & \\
63 slm, 25 min/PPA vs. 73 slm, 10 min/PPA & 0 & 0 & 1 & \\
73 slm, 15 min/PPA vs. 73 slm, 10 min/PPA & 0 & 0 & 1 & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Results of repeated-measure one-way ANOVA (RM-ANOVA), followed by Holm–Sidak comparison.  
Figure 2: Growth of _Pythium_ mycelia (mm + SE) over a 14-day period for the six different treatments. Four independent runs with seven replicates per treatment were applied (\(n=28\)). PC: positive control, inoculated no PPA, two controls using gas flow of air only without microwave torch ignition (gas only) and three different PPA treatment modes. (PPA): Note that data points for PPA treatments (blue, red, green dots) are overlaying.