## 1 Introduction  
The muskmelon (_Cucumnis melo_) is a species of melon that has been bred into several cultivated varieties worldwide. In Thailand, the cultivation of muskmelons has increased due to market demand, as observed by the Department of Agricultural Extension, Ministry of Agriculture and Cooperative, Thailand. However, Thailand is located in tropical and subtropical zones, in which the weather is favorable for pathogen germination and disease dispersal. The cultivation of muskmelons is complicated by several diseases that reduce both the quality and quantity of pre-harvest and postharvest production. Postharvest fruit rot is considered one of the most destructive diseases that negatively impact saleable stock. This disease has recently been reported to be caused by _Fusarium incarnatum_[1] in Thailand.  
The application of high doses of chemical fungicide has effectively controlled plant fungal diseases. However, they cause a negative effect in terms of the pesticide resistance of pathogens [2], and can have harmful side effects for humans [3]. Biological control is considered an alternative way to control postharvest fruit rot disease. It is well known that _Trichoderma_ species have many helpful qualities, including antibiosis [4; 5; 6; 7], competition for nutrients and space [8], mycoparasitism [9], and induction of systemic resistance [10; 11; 12] to control disease pathogens, as well as to promote plant growth ability [13].  
Endophytes are well known as a source of novel biologically active secondary metabolites that confer major ecological benefits on their host plants [14]. Antibiosis is one of the strongest mechanisms of the _Trichoderma_ species, and its endophytic relationship in nature provides a better combination of defense responses against several plant pathogenic fungi [11; 15]. The compounds released by endophytic fungi may benefit the host plant by contributing antifungal activity [16], and offer a defense against plant pathogens [17]. Endophytes are a successful biological control agent (BCA) also capable of secreting volatile organic compounds (VOCs) and cell-wall-degrading enzymes to inhibit the fungal growth involved in antibiosis. Some _Trichoderma_ species produce nonvolatile and volatile compounds responsible for inhibiting pathogens [4; 5; 6; 18; 19; 20; 21], and may directly trigger the defense system in host plants [6; 11; 22].  
_Trichoderma_ species play an important role as a BCA controlling diseases in a wide variety of plants, but the mode of action for this antagonism remains unclear. It is known that several _Trichoderma_ species produce volatile organic compounds (VOCs) responsible for inhibiting pathogens, activating a defense response as well as increased plant growth. Therefore, the present study focuses on the potential of VOCs emitted by endophytic _Trichoderma_ as a biofumigant against postharvest fruit rot disease in muskmelons caused by _F. incarnatum_. Endophytic fungi _Trichoderma_ spp. were screened for their antifungal activities, and attempts were made to determine the antagonistic mechanisms that may be responsible for suppressing _F. incarnatum_ and controlling postharvest fruit rot.