Biological control of tomato leaf curl New Delhi virus using cucurbitaceous endophytes in bitter gourd (Momordica charantia)

Momordica charantia L., known as bitter gourd, is a vine species classified under the Cucurbitaceae family and is extensively cultivated across Southeast Asia. The tomato leaf curl New Delhi virus (ToLCNDV), a member of the Begomovirus genus and Geminiviridae family, significantly affects bitter gourd. In this study, endophytes were isolated from different cucurbitaceous crops. The germination potential of the bacterial and actinobacterial isolates was evaluated via the roll towel method. Notably, isolate B-BGR1 demonstrated a 100 percent germination rate with vigor index of 5636.00 compared with the sterile water control, which presented a vigor index of 1013.00. Subsequent pot culture experiments indicated that a 2 percent application of B-BGR1 resulted in the lowest disease incidence, with a 78.57 percent reduction over the control, followed by B-BGL1, which showed a 71.43 percent reduction over the control. The isolate B-BGR1 was molecularly confirmed as Bacillus licheniformis through sequencing. The presence of secondary metabolites in B. licheniformis was identified via gas chromatography-mass spectrometry (GC-MS). To further explore the mechanism of action, the ToLCNDV coat protein was designed via MODELLER software, yielding a model with the highest DOPE score of -22439.755859. Molecular docking experiments revealed strong binding affinities for compounds 7,9-di-tert-butyl-1-oxaspiro(4,5)deca-6,9-dien and Mandelic acid, with values of -5.0 and -4.9 kcal/mol, respectively. This study represents the first investigation to confirm the antiviral potential of B. licheniformis through molecular docking against the ToLCNDV coat protein. These results indicate that B. licheniformis is a potential biological control agent for managing ToLCNDV in bitter gourd.