## 1 Introduction  
_Fusarium graminearum_, a major pathogen causing Fusarium head blight (FHB) in wheat and other cereal crops, is regarded as one of the most devastating and prevalent fungal phytopathogens due to its economic importance and trichothecene toxicity [1, 2]. _F. graminearum_ can also result in seedling blight in major grain cereal crops, which damages seedlings and reduces plant establishment, consequently leading to substantial yield loss and crop quality reduction [3]. Currently, fungal disease management mainly relies on chemical fungicides (e.g., carbendazim and tebuconazole). Though the application of chemical fungicides efficiently inhibits _F. graminearum_ infection, the indiscriminate use of fungicides has been confirmed to pose extensive adverse effects, such as increasing fungicide resistance, threatening human and animal health, and causing serious environmental pollution [4]. Therefore, it is essential to develop environmentally friendly alternative strategies with low toxicity to effectively suppress _F. graminearum_ infection. Among the alternatives, biological agents (BCAs) for preventing phytopathogens are attracting widespread attention. _Streptomyces_ spp. are the most abundant genus of actinobacteria with great potential to secrete multiple secondary metabolites [5; 6; 7]. Recently, _Streptomyces_ spp. have been reported to efficiently inhibit a broad spectrum of fungal disease, e.g., Fusarium cotton wilt [8], wheat stripe rust [9], and tomato gray mold [10]. _Streptomyces_ spp. mitigate pathogen infection in plants by different mechanisms, including the synthesis of antibiotics, mycoparasitism, physical displacement, competition, and the induction of plant systemic resistance [8; 11]. Some _Streptomyces_ species are plant growth-promoting streptomyces (PGPSs) that have established favorable interactions with plants [12; 13; 14]. Generally, PGPSs promote plant growth via a variety of mechanisms, including nitrogen fixation, phytohormone generation, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, and siderophore production, thereby alleviating abiotic or biotic stress to plants [8; 15]. For instance, _S. hygroscopicus_ TP-A0451 generates pteridic acid A and B with auxin-like activity, inducing adventitious root formation and stimulating root elongation in _Phaseolus vulgaris_ hypocotyls [16]. _S. filipinensis_ no. 15 reduces the endogenous level of ACC, consequently improving the resistance of tomato plants to abiotic and biotic stress [17]. Siderophore compounds are potential plant growth promoters and disease suppressors [18]. _Streptomyces_ spp. were reported to promote their colonization in plants by producing siderophores, as well as assist in obtaining iron nutrition and limit and inhibit the growth of plant pathogens through iron competition [19]. Except for plant growth-promoting (PGP) properties, _Streptomyces_ spp. have been demonstrated to induce resistance in plants to counteract pathogen infection [9]. Induced resistance (IR) has been investigated widely in numerous plant-pathogen interactions. Generally, IR is divided into induced systemic resistance (ISR) and systemic acquired resistance (SAR) [20]. ISR is a systemic resistance activated by nonpathogenic microbes that inhibit pathogen invasion [21]. Ethylene (ET) and jasmonate (JA) exert important modulatory roles in ISR [11]. Beneficial microbes activate ISR via triggering the plant for potentiated initiation of different cellular defense responses, such as ROS accumulation, callose deposition, defensed-related enzyme enhancement, and cell wall reinforcement [11; 22]. In contrast, SAR is an induced resistance that occurs throughout the plants in response to a temporally earlier local exposure to a pathogen, which needs the biosynthesis of phenolic signaling compounds, such as salicylic acid (SA) [20]. Nevertheless, it was reported that antagonistic relationships occur between the JA/ET and SA pathways, and synergistic JA/ET and SA pathway interactions have also been detected.