# Volatile Organic Compound from _Trichoderma asperelloides_ TSUI: Impact on Plant Pathogenic Fungi
## 4 Discussion  
In this study, a soil fungus was isolated and identified on the basis of morphology and molecular techniques, and antifungal activity against plant diseases was examined. The isolated fungus was identified as _T. asperelloides_ TSU1 (Figures 1 and 2). This isolate was documented as being capable of emitting 17 VOCs, and results indicate that its VOCs were responsible for the in vitro inhibition of fungal growth for some airborne, soilborne, and postharvest pathogens (Figures 3 and 4). The antifungal activity of the VOCs from this isolate was comparable to the adverse activity of commercial 2-PE against the same group of tested fungal plant pathogens. Interestingly, the commercial 2-phenylethanol showed antifungal activity against fungal pathogens that was similar to the VOCs of _T. asperelloides_ TSU1 by bioassay.  
Low-molecular-weight volatile phase compounds produced by growing _Trichoderma_ species are chemically diverse and possess antimicrobial properties. The antifungal activity of _T. asperelloides_ TSU1 VOCs that suppress the growth of fungal pathogens is correlated with the presence of 2-PE. The volatile eight-carbon compound 2-PE is an important element that imparts flavor and taste in food with a rose-like aroma. Interestingly, 2-PE showed antifungal ability against plant diseases. For instance, [PERSON] et al. [45] applied 2-phenylylethanol isolated from _Kloeckera apiculata_ to control the _Penicillium_ mold of citrus. Here, _T. asperelloides_ TSU1 produced VOCs that contained 2-PE, and effectively inhibited the growth of fungal pathogens (Figures 6 and 7). Therefore, the ability to produce antifungal compounds of _T. asperelloides_ TSU1 may control several plant diseases.  
The ability to produce VOCs by endophytic fungus _T. asperelloides_ strain PSU-P1 was recently reported to inhibit fungal pathogens, induce a defense response, and promote plant growth in _Arabidopsis thaliana_[16]. Our result agrees with those reporting that _T. asperelloides_ TSU1 produces VOCs to inhibit the growth of plant pathogens (Figure 3). The pattern of the antifungal ability of VOCs and commercial 2-PE is seemed to be differed (Figures 4 and 7). The effects of the volatiles from the fungus were more effective on _C. cassiicola_ than on _S. rolfsii_ (Figure 4), while the results in Figure 7 show a lower effect on _C. cassiicola_ and a higher effect on _S. rolfsii_. This phenomenon may be explained by how volatiles of _Trichoderma_ were produced and released in a complex mixture containing 17 compounds; some compounds might work synergistically to inhibit fungal growth with more effective inhibition than with single compounds [15]. For a commercial volatile, pure 2-PE was used, which may affect the different inhibitions against plant pathogens. Furthermore, fungi produce a wide range of different types of hyphae; therefore, the effect of the volatile mixture and the single compound may also differ, resulting in different inhibitory activities in the bioassay.  
[PERSON] et al. [16] recently revealed that _T. asperelloides_ PSU-P1, an endophytic fungus, released major volatile compounds (namely, 2-methyl-1-butanol and 6-pentyl-2H-pyran-2-one) responsible for antifungal ability. Our results demonstrated that a different strain of the same species, _T. asperelloides_ (TSU1), released 2-PE. This study provides evidence that VOCs emitted from _T. asperelloides_ TSU1 have antifungal effects against some plant pathogens and could be used as a suitable alternative to synthetic fungicides. Biofumigation by microorganisms is an alternative way to control postharvest diseases that is environmentally friendly and less toxic to human health.