## 1 Introduction  
Pears are among the most popular and important fruits in China, which is the global leader in pear production. The rapid expansion of the pear cultivation area, together with suboptimal cultivation practices and climatic factors, however, have threatened the integrity of pear crops owing to widespread outbreaks of pear Valsa canker caused by _Valsa pyri_, which is most common in northern, northwestern, and northeastern China [1, 2]. In some orchards, up to 100% of pear trees are diseased, adversely impacting the sustainable development of the pear industry. Pear Valsa canker primarily impacts the lateral and main branches of pear trees, contributing to bark rot, necrosis, overall tree weakness, and yield losses [3, 4]. A series of integrated control strategies are typically employed in an effort to protect against this disease, with fungicides application remaining the most effective and direct approach to controlling pear Valsa canker. However, the widespread and prolonged use of fungicides can impose greater levels of selective pressure on the causative pathogen, in addition to polluting the surrounding environment and negatively affecting food safety, thus limiting the utility of fungicides. There is thus a pressing need for alternative approaches to the reliable prevention and control of this potentially devastating disease. Endophyte-based biocontrol strategies have emerged as an environmentally friendly alternative to more traditional fungicide use [5]. Several microbes have been shown to effectively facilitate the control of pear Valsa canker to date, such as _Paenibacillus polynyxa_ (strain Nl4), _Bacillus velezensis_ (strain D4), _Lysobacter enzymes_ (strain OH11), and _Penicillium citrimum_ (strain ZZ1) [6; 7; 8; 9]. While these biocontrol agents exhibit promising applications, just one has been registered in China to date. As such, there is value in the further exploration of other stable and effective antagonistic biocontrol strategies that can help mitigate the spread of pear Valsa canker. The biocontrol agent _B. atrophaeus_ has shown great promise with respect to its ability to suppress the growth of a range of plant pathogens, including _Colletotrichum gloeosporoides_, _Alternaria alternata_, _Fusarium oxysporum_, _C. nymphhaea_, _Rhizoctonia solani_, and _Botryosphareia dothidea_[10; 11; 12; 13; 14; 15]. However, few studies to date have focused on the application of _B. atrophaeus_ as a biocontrol agent capable of preventing plant diseases caused by _V. pyri_. Mechanistically, _B. atrophaeus_ can antagonize pathogen growth by competing for space and nutrients, engaging host defense responses, and/or producing antimicrobial compounds [16]. The production and secretion of bioactive compounds that suppress pathogen growth is the primary antagonistic mechanism utilized by this species. A variety of antagonistic compounds have been characterized to date, including lytic enzymes and peptides that are released into the extracellular environment [16]. _B. atrophaeus_ strain CAB-1 has been shown to secrete lipopeptides with robust inhibitory activity against _Botrytis cinerea_[17]. Biocontrol agents are also capable of emitting VOCs that can strongly suppress the growth and survival of plant pathogens [18; 19; 20]. _B. atrophaeus_ strain L193, for example, can produce VOCs that readily suppress mycelial growth for pathogenic species, including _Monilitia fructicola_, _Sclerotinia sclerotorium_, and _M. laxa_, while also reducing the incidence of _M. laxa_-associated disease [19]. These prior reports thus highlight the promise of _B. atrophaeus_-derived VOCs as candidate biocontrol agents. There is thus clear value in research focused on identifying and characterizing a range of VOCs with antimicrobial activity. To date, researchers have reported several _B. atrophaeus_-derived VOCs with antagonistic activity, including O-anisaldehyde, chloroacetic acid tetradecyl ester, hexadecanoic acid methyl1 ester, and octadecane [17; 18]. Here, _B.