Target and non-target effects of dual inoculation of biocontrol agents against Fusarium wilt in Solanum lycopersicum

Bacillus subtilis and Trichoderma harzianum are known for their antagonistic potential against several fungal phytopathogens. However, limited studies have assessed the non-target effects of these biocontrol agents. The present study aimed to investigate the antagonistic efficacy of B. subtilis (MTCC 2274) and T. harzianum (MTCC 3928) in mitigation of Fusarium wilt, and to study their non-target effects on the rhizospheric bacterial community in tomato. In planta assay revealed that the consortium of B. subtilis and T. harzianum exhibited the highest disease reduction (56%), whereas with chemical control it was 48.7% as compared to untreated control. Also, the impact of the dual inoculation on the bacterial community was qualitatively and quantitatively monitored by PCR-denaturing gradient gel electrophoresis (DGGE) and qPCR, respectively by employing 16S rRNA as a marker. DGGE profiles generated from rhizospheric samples from treatment (90 DAS) with T. harzianum and B. subtilis, and chemical treatment formed a cluster with 72% similarity. The phylogenetic analysis of excised bands showed the presence of ecologically important species (Desulfotomaculum thermoacetoxidans, Microcoleus sp., Thermoactinomyces sp. and Nocardioides sp.) in soil treated with dual inoculation. Furthermore, qPCR of rhizospheric soil (90 DAS) treated with both inoculants showed a 16S rRNA gene copy number/g dry soil of 2.9 x 10(4) in comparison to untreated control (8.8 x 10(3)) that confirmed the positive change in bacterial abundance. These results demonstrated the integrated role of biocontrol agents towards soil health improvement along with mitigation of Fusarium wilt.