Endophytic Colletotrichum causes apoptosis-mediated cell death in Spodoptera frugiperda cells: implications for biocontrol and pest management

Endophytic fungi symbiotically reside within plant tissues without eliciting apparent pathological responses. Positive interactions between endophytic fungi and plants help the host overcome biotic and abiotic stressors. Spodoptera frugiperda is a fall armyworm that devastates the revenue of farmers worldwide and is a major threat to food security. Here, we investigated the cytotoxicity of extracts of endophytic fungi isolated from brinjal (Solanum melongena L.) var. Mattu Gulla on the insect cell line Sf21 (Spodoptera frugiperda ovarian cells). Among the 13 endophytic fungi tested, Colletotrichum sp. presented the greatest cytotoxic ability, with an IC₅₀ of 103.6 µg mL⁻¹. LC‒MS analysis revealed the presence of several fungal metabolites (232), and 12 metabolites were identified, among which regiolone is known to have potent insecticidal activity. The fungal extract disrupted oxidative homeostasis in Sf21 cells by increasing the total reactive oxygen species (ROS) content according to the treatment concentration and duration. The mitochondrial membrane potential analysis by flow cytometry indicated the presence of depolarized mitochondria in cells treated with the fungal extract. Furthermore, fragmented mitochondria and clear signs of apoptosis, including nuclear condensation, the presence of necklace, ring-like structures and collapsed nuclei, were observed. Our data revealed that the Colletotrichum sp. extract had cytotoxic effects by inducing apoptosis in vitro, which could be explored with respect to the Colletotrichum sp. extract in further investigations.