## 3 Discussion
** Compound**
* **Ff** & **H** & **Mf** & **Mo** & **Pz** & **Rs** \\ \hline
1 & Dimethyl trisulfide & \(100\pm 0.00\) & \(100\pm 0.00\) & \(100\pm 0.00\) & \(100\pm 0.00\) & \(100\pm 0.00\) & \(100\pm 0.00\) \\
2 & Allyl benzyl ether & \(53.48\pm 0.79\) & \(25.86\pm 0.41\) & \(61.53\pm 2.21\) & \(36.65\pm 1.18\) & \(78.32\pm 0.51\) & \(56.28\pm 0.94\) \\
3 & Methyl benzoate & \(70.36\pm 0.54\) & \(83.15\pm 1.29\) & \(11.37\pm 0.31\) & \(85.64\pm 2.58\) & \(100\pm 0.00\) & \(67.29\pm 0.68\) \\
4 & Benzyl acetate & \(67.45\pm 0.86\) & \(65.16\pm 4.60\) & \(38.81\pm 1.63\) & \(91.29\pm 1.47\) & \(40.29\pm 0.63\) & \(74.68\pm 1.34\) \\
5 & Methyl salicate & \(82.72\pm 0.22\) & \(87.76\pm 1.38\) & \(100\pm 0.00\) & \(100\pm 0.00\) & \(100\pm 0.00\) & \(65.05\pm 1.41\) \\
6 & Benzyl propionate & \(79.65\pm 1.87\) & \(73.38\pm 0.77\) & \(18.05\pm 0.92\) & \(79.59\pm 0.71\) & \(80.92\pm 1.27\) & \(36.21\pm 0.30\) \\
7 & Nonanoic acid & \(78.85\pm 3.37\) & \(100\pm 0.00\) & \(52.38\pm 0.38\) & \(44.21\pm 1.05\) & \(62.02\pm 0.61\) \\
8 & Indole & \(100\pm 0.00\) & \(100\pm 0.00\) & \(100\pm 0.00\) & \(100\pm 0.00\) & \(100\pm 0.00\) & \(100\pm 0.00\) \\
9 & Methyl anthranilate & \(83.75\pm 0.31\) & \(90.54\pm 0.64\) & \(18.44\pm 0.37\) & \(100\pm 0.00\) & \(58.12\pm 0.74\) & \(84.87\pm 0.97\) \\
10 & 3-5 Di-tert-butylphenol & \(77.08\pm 0.14\) & \(77.65\pm 0.68\) & \(27.69\pm 1.19\) & \(81.35\pm 0.48\) & \(84.36\pm 1.75\) & \(82.31\pm 1.82\) \\
11 & 3-Hexen-1-ol, & & & & & & \\
12 & 2-Pentadecanone & - & - & - & - & - & \(13.74\pm 0.27\) \\
13 & Dodecanamide & - & - & - & - & - & - \\
14 & Benzyl benzoate & - & - & - & - & - & \(10.52\pm 1.17\) \\ \hline \hline \end{tabular}  
* Note: “-” indicates no antifungal activity. Data were presented as means \(\pm\) standard error. Twelve different fungal strains including _A. alternate_ (Aa), _A. Aspergillus niger_ (An), _B. sorokiniana_ (Bs), _B. Cinnera_ (Bc), _F. solani_ (Fs), _F. oxysporum_ (Fo), _F. frijkuru_ (F), _H. torulosum_ (H), _M. fijensis_ (Mf), _M. oryzae_ (Mo), _P. zlonger-distance range of action, and degrade easily [35]. In our study, we found that the VOCs produced by ETR-B22 showed strong antagonistic activity against a variety of fungal pathogens. Although ETR-B22 had a wide-spectrum antifungal activity against all of the tested fungal pathogens, genus-genus or species-species differences were observed. For instance, compared to _Fusarium_ species, some genera were more sensitive. Similarly, within the same genus, some species were more sensitive than others. Comparing the inhibition rate of the VOCs against the three _Fusarium_ species, it was found that the inhibition rate against _F. solani_ was higher than that of _F. fujikuroi_. This result may be explained by antifungal mechanisms or chemical differences among taxa. For _Burkholderia_ spp., similar results have been reported by other authors. For instance, the VOCs produced by a _B. gladioli_ strain exert antifungal activity against plant pathogenic fungi by producing diffusible metabolites [36]. The VOCs produced by _B. tropica_ inhibited the growth of fungal pathogens mycelium and disrupted fungal hyphae [37]. To the best of our knowledge, our study was the first to report that the antifungal and biological control potential of VOCs produced by endophytic _B. encocpacia_ that significant growth inhibition (i.e., 75%+ suppression rate) was found for six fungi, while three were below 50% growth inhibition. Our results suggest that the VOCs produced by ETR-B22 represent an effective biocontrol tool to protect plants against pathogen infection. Solid phase micro-extraction technology was used to extract VOCs. The extraction temperature and time are the main factors that determine the efficiency of extraction. In this study, 40 \({}^{\circ}\)C for 30 min was considered the optimal condition to extract VOCs from ETR-B22 strain (Figure 4). Even though there have been some studies about different extraction temperature and time of VOCs produced by Burkholderiaceae, little is known about the optimal combination.