## 3 Results  
### Thermodynamic Background for Control of Rhizoctonia solani AG 2-2 IIIB  
To develop the approach of effective control of the phytopathogenic fungus _Rhizoctonia solani_ AG 2-2 IIIB, a method of thermodynamic prediction was applied to consider the key conditions of the environment that affect its growth. The field of water stability in the coordinates of pH and Eh was studied to highlight the optimal conditions as well as those causing inhibition and death of the fungus. We applied classical Pourbaix diagrams adapted for biological systems [26; 30]. In biology, microbiology, and biochemistry, standard potentials (E\({}_{0}\)\({}^{\prime}\)) are calculated for pH = 7.0 at a one-molar concentration of reacting components and a temperature of 25 \({}^{\circ}\)C [31] (Figure 1). Under these conditions, the zone of water stability is in the range of standard redox potentials from E\({}_{0}\)\({}^{\prime}\) = \(-\)414 mV (lower limit) to E\({}_{0}\)\({}^{\prime}\) = \(+\)814 mV (upper limit). Water has the properties of a binary redox buffer. At the values of redox potential E\({}_{0}\)\({}^{\prime}\) \(>\)\(+\)814 mV, water oxygen (O\({}^{2-}\)) acts as a reducing agent and is oxidized to molecular oxygen O\({}_{2}\):  
\[2\mathrm{H}_{2}\mathrm{O}=\mathrm{O}_{2}+4\mathrm{H}^{+}\ \mathrm{(reaction\ No.\ 1).}\]  
Clearly, the redox potential of water returns to its original value, i.e., to E\({}_{0}\)\({}^{\prime}\) = \(+\)814 mV. At the values of redox potential E\({}_{0}\)\({}^{\prime}\)\(<\)\(-\)414 mV proton (H\({}^{+}\)) serves as the oxidizer. If the redox potential of the solution is less than \(-\)414 mV, two protons (2H\({}^{+}\)) will be reduced to H\({}_{2}\) and the potential will return to initial value E\({}_{0}\)\({}^{\prime}\) = \(-\)414 mV:  
\[2\mathrm{H}^{+}+2\mathrm{e}=\mathrm{H}_{2}\ \mathrm{(reaction\ No.\ 2).}\]  
That is why the whole diversity of bioenergetic reactions are possible only within the zone of the thermodynamic stability of water, i.e., in the E\({}_{0}\)\({}^{\prime}\) range from \(-\)414 to \(+\)814 mV. Microorganisms efficiently use redox reactions in a wide range of water stability potentials to obtain energy. Thus, microorganisms use reaction No. 1 for both aerobic metabolism (C\({}_{\mathrm{organic}}\) + 2O\({}_{2}\) + 4H\({}^{+}\) = CO\({}_{2}\) + 2H\({}_{2}\)O) and photosynthesis (CO\({}_{2}\) + 2H\({}_{2}\)O + \(h\eta\) = C\({}_{\mathrm{organic}}\) + 2O\({}_{2}\) + 4H\({}^{+}\)). Reaction No. 2 is used by microorganisms, for example, for hydrogen fermentation (C\({}_{6}\)H\({}_{2}\)O\({}_{6}\) + 4H\({}^{+}\) = 2H\({}_{2}\) + CO\({}_{2}\) + CH\({}_{3}\)COOH) and methanogenesis (4H\({}_{2}\) + CO\({}_{2}\) = CH\({}_{4}\) + 2H\({}_{2}\)O). Figure 1: Thermodynamic calculations of zones compatible and incompatible with the life of _Rhizoctonia solani_ AG 2-2 IIIB: upper (a) and lower (b) limits of water stability in the E\({}_{0}\)\({}^{\prime}\) range from \(+\)814 mV to \(-\)414 mV; c—separation of aerobic and anoxygenic zones. Upper limit of water stability is described by reaction 2H\({}_{2}\)O = O\({}_{2}\) + 4H\({}^{+}\) and equation E\({}_{0}\)= 1.228–0.0591 \(\times\) pH—0.0295 \(\times\) lgPH\({}_{2}\), where PH\({}_{2}\) is partial pressure of hydrogen. Lower limit is described by reaction 2H\({}^{+}\) = 2e = H\({}_{2}\) and equation E\({}_{0}\)= 0.000–0.0591 \(\times\) pH \(\times\) lgPH\({}_{2}\). The application of thermodynamic prediction to suppress the growth of microorganisms, in fact, is the calculation of zones that are incompatible with the life of this organism depending on pH and Eh. To achieve the suppression or death of the investigated strain, it is necessary to create corresponding conditions using physicochemical factors, biological factors (microbiome, etc.) or combination of them. Therefore, we calculated the thermodynamic conditions taking into account the physiological characteristics of _Rhizoctonia solani_ AG 2-2 IIIB (Figure 1). _R.