## 1 Introduction  
Plant fungal pathogens cause diverse crop diseases resulting in drastic economic losses worldwide [1]. Improving the control of plant fungal diseases is an effective method for solving food shortage issues around the world [2; 3]. Traditionally, chemical fungicides have been used to control fungal pathogens. However, intensive use of synthetic fungicides can cause problems such as pathogen resistance, fungicide residues, and environmental pollution [4; 5; 6]. There is an urgent need for environmentally friendly and effective agents to satisfy stricter agricultural product safety standards and increasing public concern.  
The use of biocontrol microorganisms has attracted attention as a potential alternative to chemical measures in the control of plant pathogenic fungi [7]. Many antagonistic microorganisms,e.g., _Bacillus_[8], _Pseudomonas_[9], and _Burkholderia_[10], exhibit biocontrol activity that can control the growth of plant fungal pathogens. The antagonism of fungal pathogens by microorganisms mainly depends on their secretion of antimicrobial active compounds [11], competition for nutrients and living space [12], hyperparasitism and induction of systemic resistance responses in the host [13], and secretion of cell wall degrading enzymes (CWDEs) [14]. Additionally, volatile organic compounds (VOCs) released by microorganisms receive attention due to their antimicrobial effects [15; 16]. Recently, VOCs produced by microorganisms were proposed as an alternative control method for fungal plant diseases because they can influence pathogenic fungal growth, deforming fungal hyphae and spores [17]. For instance, several VOCs (e.g., Pyrazine (2,5-dimethyl), benzothiazole, 4-chloro-3-methyl, and phenol-2,4-bis (1,1-dimethylethyl)) produced by _Bacillus velezensis_ ZSY-1 exhibit significant antifungal activity against _Alternaria solani_ and _Botrytis cinerea_[18]. On the other hand, VOCs can promote growth and induce systemic resistance in plants [19; 20]. Therefore, it is suggested that VOCs from microorganisms are an important source for screening antimicrobial compounds and developing biological control agents (BCAs).  
Endophytes, which colonize and survive in plants without damaging hosts or causing disease symptoms, are a better potential BCA resource [21]. Investigations show that endophytes also have different kinds of ecological functions, such as biocontrol activity [22], promotion of plant growth [23], and modulation of plant systemic resistance [24]. However, the VOCs emitted by endophytes have been overlooked due to the unique endophyte habitat. Therefore, increasing research effort in antimicrobial VOCs produced by endophytes seems particularly relevant.  
_Sophora tonkinensis_ Gagnep. is widely used as a traditional medicine and plant botanical fungicide source [25; 26]. In a previous study, our laboratory screened and named the endophytic bacterium strain ETR-B22 isolated from the root of _S. tonkinensis_, which exhibited significant antifungal activity. However, its mechanism of antifungal action has not been fully elucidated. Therefore, the objective of this study was (1) to evaluate the antagonistic effects of stain ETR-B22; (2) to assess broad-spectrum antifungal effects of VOCs produced by strainETR-B22; (3) to identify and characterize the composition of the VOCs; and (4) to determine the chemical factors in pathogen inhibition.