## 4 Discussion  
The management of plant pathogens in the process of crop production is crucial, no matter whether organic, integrated, or conventional farming practices are applied. Figure 4: The influence of \(\beta\)-caryophyllene and \(\beta\)-caryophyllene oxide on the growth of plant growth-promoting bacteria. Final concentrations of 62.5 \(\mathrm{\SIUnitSymbolMicro mL^{-1}}\), 125 \(\mathrm{\SIUnitSymbolMicro mL^{-1}}\) and 250 \(\mathrm{\SIUnitSymbolMicro mL^{-1}}\) of \(\beta\)-caryophyllene (grey bars) and \(\beta\)-caryophyllene oxide (blue bars) were added to cultures of _R. rhizgenes_ (**A**), _R. capsulatus_ (**B**), _B. subtilis_ (**C**), _P. Polymyx_ (**D**), _P. fluorescens_ (**E**) and _P. putida_ (**F**) in 100 \(\mathrm{\SIUnitSymbolMicro m}\) medium (_R. capsulatus_ in RCV medium) in MTPs. The final solvent concentration was 1% (\(\
icefrac{{v}}{{v}}\)) Tween 20 and 0.5% (\(\
icefrac{{v}}{{v}}\)) DMSO. To determine the influence of the terpen on the growth of the bacteria, the cells were incubated stationary for 20 h at 37 \({}^{\circ}\)C (_R. capsulatus_ at 30 \({}^{\circ}\)C) and the cell density was measured at 625 \(\mathrm{\SIUnitSymbolMicro m}\) using a plate photometer. The solvent control (control, black bars) was MH or RCV medium containing 1% (\(\
icefrac{{v}}{{v}}\)) Tween 20 and 0.5% (\(\
icefrac{{v}}{{v}}\)) DMSO. Values are means of three independent biological replicates (\(n=3\)) and error bars indicate the respective standard deviations. For many decades, synthetic pesticides were considered the fastest and most effective pest and pathogen control method. Recently, due to the rise of public health concerns about pesticide toxicity and harm to the environment, many of these effective chemicals were banned, thereby markedly limiting the options for plant protection. Therefore, it is important to find environmentally safe and sustainable natural products to control pathogens and thus ensure yield and food quality. In this context, plant metabolites are a rich source of bioactive compounds explorable for the use of preventing and controlling plant pathogenic microbes. In the last decade, several studies investigated terpenoids as potential antihypotopathogenic compounds [67; 71; 76; 77; 108; 109]. \(\beta\)-caryophyllene is a natural bicyclic sesquiterpene that is a constituent of many essential oils. Many studies showed that these essential oils, which are containing \(\beta\)-caryophyllene as one of the main ingredients, are active against plant pathogens [109; 110; 111]. For example, methanol extracts from _Artemisia annua_ leaves, one of the common \(\beta\)-caryophyllene producers, strongly inhibit the growth of the plant pathogenic fungi _F. oxysporum_ and _Fusarium solani_[79]. In another study, the essential oil from _Murraya paniculata_ leaves showed inhibitory activities on the mycelial growth of _S. scleroorum_, a fungus that poses a high risk to several crops. The gas chromatography analysis of the essential oil composition introduced \(\beta\)-caryophyllene as one of the main constituents (23.8%) [109]. Furthermore, essential oils from _Piper aduncum_, which also has \(\beta\)-caryophyllene as one of its main constituents (7.2%), inhibited the mycelial growth of the fungus _S. scleroorum_[110]. As a second alternative or complementary means for plant protection, there is also a multitude of important and useful microorganisms that support plant growth, which are called plant growth-promoting bacteria and plant growth-promoting fungi (PGPF). To offset the negative effects of chemical substances or make their use superfluous, more and more PGPB are now being used in agriculture [112]. Microorganisms can fulfill different functions in this process. _Bacillus subtilis_, for example, accumulates at the root system during the germination of various plants and prevents competing harmful fungi from spreading [103]. Diazotrophic organisms can supply plants with biologically available nitrogen by fixing atmospheric dinitrogen, thus making it available to the plants [113].