Plants release a variety of defensive volatiles in response to biotic stress. The present study examined interactions between and the defense volatiles induced by this fungal species in the tea cultivar "Qiancha No. 1". Analysis of the volatiles emitted from -infected leaves of "Qiancha No. 1" revealed that four volatiles showed a relative content increase of more than 2%. Fungicidal activity assays demonstrated that decanal exhibited the strongest antifungal activity among the four volatiles. Further physiological experiments demonstrated that the antifungal mechanism of decanal was associated with disruption of the cell wall and the membrane. Transcriptome analysis revealed that the genes encoding Chitinase 1, chitin synthase 1, and endochitinase42 were identified as potential targets that may be involved in cell wall degradation by decanal. Additionally, genes encoding cytochrome P450-DIT2 and multidrug resistance protein fer6 were identified as potential targets that may be associated with membrane damage. This study is the first to demonstrate that decanal acts as a direct defense volatile in the interaction between and "Qiancha No. 1," highlighting its potential as an effective antifungal agent.