## 3 Results and Discussion  
Plant growth-promoting rhizobacteria (PGPR) have been applied to a wide range of agricultural crops for the purpose of growth enhancement, including increased seed germination, plant weight, and yield [12, 13]. A number of mechanisms have been suggested for rhizobacteria-mediated plant growth promotion: (i) increased phosphate solubilization [14]; (ii) secretion of plant growth-promoting substances such as auxins and cytokins [15, 16] and (iii) production of antibiotics and hydrogen cyanide, which indirectly promote plant growth by inhibiting the growth of deleterious microorganisms in the rhizosphere [17]. Our results showed that the fungal plant growth promoting agent CL-1 significantly improved the growth of tobacco seedlings and their root development through the production of VOCs (Figures 1 and 2). Volatiles could be an effective tool for rhizosphere microorganisms to influence neighboring organisms because they are small molecules that can easily diffuse through porous soils and travel over a long distance via the atmosphere. [PERSON] _et al_. [10] showed that certain bacterial VOCs function as signaling molecules for mediating plant-microbe interactions. They identified 2,3-butanediol and acetoin as VOCs that promoted the growth of _Arabidopsis thaliana_. [PERSON] _et al_. [18], using SPME-GC-MS, identified an array of volatile compounds emitted from rhizobacteria that are involved in plant growth promotion. The capability of _Trichoderma_ spp. to produce a great number of volatile secondary metabolites (e.g., pyrones, sesquiterpenes) has been reviewed [19]. Volatile secondary metabolites have been demonstrated to play a key role in mycoparasitism of _Trichoderma_ as well as its interaction with plants [4]. Our analysis of CL-1 volatiles using SPME/Quadrupole GC/MS/MS revealed that CL-1 emits the volatiles \(\alpha\)-pinene, (-)-_trans_-caryophyllene, tetrahydro-2,2,5,5-tetramethylfuran, dehydro- aromadendrene, and (+)-sativene (Figures 3 and 4), which might have contributed to the enhanced seedling growth of tobacco. Monoterpenes including \(\alpha\)-pinene are known to play important chemo-ecological roles in the interactions between plants and their environments, often playing a protective role against herbivores and pathogens [20]. [PERSON] _et al_. [21] reported that \(\alpha\)-pinene at concentrations of 0.05-1.0 mM stimulated germination, primary root growth, and mitochondrial respiration of maize. Although at very high concentrations \(\alpha\)-pinene has been reported to adversely affect plant growth and development [22]. The mechanisms by which monoterenes affect seed germination are not known. The volatile sesquiterpene _trans_-caryophyllene is a major component in the essential oils of various medicinal plants, but its plant growth promoting effect has not yet been described. [PERSON] _et al_. [11] reported the plant-growth-promoting fungus (PGPF), _Talaromyces_ sp. emitted \(\beta\)-caryophyllene that significantly enhanced the growth of _Brassica campestris_ seedlings and their resistance to _Colletotrichum higginsianum_. [PERSON] _et al_. [23] showed that the VOC 2-pentylfuran, emitted by the PGPR _Bacillus megaterium_ strain XTBG34, caused growth promotion in _A. thaliana_. Furan compounds have been reported to exhibit plant growth regulatory properties and are therefore recommended for commercial use in agriculture to improve and control plant health. [PERSON] _et al_. [18] also showed the PGPRs _B. subtilis_ GB03 and _B. amyloliquefaciens_ IN937a emit the volatile 2-pentylfuran at very low levels. There are also reports of fungal (_Aspergillus fumigatus_, _Fusarium_ spp., _Aspergillus terreus_, _Aspergillus flavus_, _Aspergillus niger_) emission of furans [24]. Furans and their derivates are a potentially important, but poorly studied, class of VOCs and their mechanism of plant growth promotion is not well understood. Figure 2: Tobacco seedling growth promotion by volatiles of CL-1.