## 4 Discussion  
In the present study, _T. asperellum_ T16-14 exhibited antifungal activity against the mycelial growth of _F. incarnatum_, the causal microorganism of postharvest fruit rot in muskmelons. _T. asperellum_ T16-14 effectively inhibited mycelial growth of _F. incarnatum_ in vitro by a dual-culture assay, which suggested a competition mechanism (Figure 2). The sealed plate method also revealed the antibiosis mechanism of _T. asperellum_ T16-14 against _F. incarnatum_ (Figure 3). The dominant volatile compound released by _T. asperellum_ T16-14, tentatively identified as PEA based on SPME GC/MS, was involved in antifungal activity against _F. incarnatum_ (Figures 4 and 5). VOCs released by _T. asperellum_ T16-14 caused abnormal changes in the _F. incarnatum_ mycelia (Figure 6), reducing the postharvest fruit rot in muskmelons (Figures 7 and 8). In a primary screening by dual-culture assay, _T. asperellum_ T76-14 grew faster than _F. incarnatum_ on PDA (Figure 3), suggesting a competition mechanism. This mechanism is common in several species of _Trichoderma_ against plant pathogens [4; 5; 28]. In the study above, _T. asperellum_ T76-14 was found to produce VOCs (Figure 3 and Table 1) that slow the fungal growth of _F. incarnatum_. This production involved an antibiosis mechanism within the _Trichoderma_ species. It has been established that several _Trichoderma_ species emit volatile antifungal compounds that inhibit pathogen growth [4; 5; 6; 25]. In this study, volatiles emitted from _T. asperellum_ T76-14 inhibited the fungal growth of _F. incarnatum_ by 62.5% (Figure 2), as determined through the sealed plate method. The VOCs emitted by _T. asperellum_ T76-14 slow the fungal growth of _F. incarnatum_, similar to PEA. Both VOCs and PEA caused abnormal changes in the fungal mycelia (Figure 6), which may result in inhibiting the fungal growth of _F. incarnatum_. As shown in Figure 4 and Table 1, GC/MS revealed some minor peaks, which may have contributed to antifungal activity due to a low percent peak area. This revealed that the VOCs emitted by _T. asperellum_ T76-14 were responsible for the antifungal activity against _F. incarnatum_. The GC/MS results presented 17 compounds; however, according to the literature, the only antifungal compound found in this study was PEA (Figures 4 and 5). Figure 8: Lesion diameter on muskmelons in the control versus muskmelons exposed to _Trichoderma_ _asperellum_ T76-14 (T76-14) and phenylethyl alcohol (PEA). Different letters indicate statistically significant differences among treatments (_p_ < 0.05) using Tukey’s test. PEA, also known as an aromatic alcohol, is an organic compound found as a colorless liquid with a rose-like odor. This compound occurs widely in nature as an essential oil from several plant species such as roses, jasmine, carnations, and hyacinths [29]. PEA has been used to modify certain flavor compositions of foods with low toxicity [30; 31]. It has been shown that PEA has antimicrobial properties [29; 30; 32; 33; 34]. An in vitro study revealed that PEA inhibits fungal growth and the synthesis of RNA, DNA, and the protein of _Neurospora crassa_[32]. PEA has been reported to show strong antifungal activity against _Ganoderma boninense_[35], significantly reducing fungal growth to prolong the postharvest life of strawberries [34], and controlling the blue mold decay caused by _Penicillium digitatum_ and _P. italicum_ in citrus fruits [36]. Our result is in agreement with previous reports that PEA inhibited the fungal growth of _F. incarnatum_ in vitro (Table 2) and reduced lesions on muskmelon fruits (Figures 7 and 8). This also proved that PEA in VOCs released from _T. asperellum_ T76-14 had antifungal activity against _F. incarnatum_. PEA has been reported to be produced by several _Trichoderma_ species. For instance, PEA emitted by _Trichoderma_ sp. [29], _T. atroviride_[37], _T. harzianum_[38], _T. spirale_[5], and _T. virens_[36] displayed antifungal ability against several plant pathogens. In this study, PEA emitted by _T.