Bioprospecting endophytic Bacillus spp. from tomato for antagonistic potential against tomato leaf curl virus (ToLCV)

Tomato leaf curl virus (ToLCV) is one of the most destructive viral pathogens of tomato, causing severe yield losses and posing significant management challenges because of its persistent transmission by Bemisia tabaci and the rapid emergence of viral variants. In search of sustainable alternatives to chemical control, the present study investigated the antiviral potential of endophytic Bacillus spp. isolated from wild and cultivated tomato germplasm. A total of twenty-four bacterial endophytes were isolated from surface-sterilized root, stem and leaf tissues, of which six representative isolates were identified as Bacillus subtilis, B. safensis, B. pumilus and B. cereus through morphological traits and 16S rRNA gene sequencing. Greenhouse-based evaluation of antiviral activity was conducted using seed priming and foliar application of bacterial culture filtrates. Seed priming with Bacillus isolates showed limited protection, with high percent disease incidence (PDI) values (90-100 %), indicating poor suppression of ToLCV. In contrast, culture filtrates demonstrated strong isolate-specific antiviral effects. Notably, B. subtilis isolates GSB1 and HLB1 recorded the lowest PDI (46.67 %), significantly delaying symptom onset and reducing disease severity, followed by moderate activity from B. safensis (HSB2). The remaining isolates showed minimal efficacy. The superior performance of culture filtrates suggests that bioactive metabolites produced by certain Bacillus strains may induce systemic resistance and/or interfere with viral infection processes. Overall, the study highlights the potential of tomato-associated endophytic Bacillus spp. particularly B. subtilis as promising candidates for developing environmentally safe biocontrol strategies against ToLCV.