Diversity and antiviral potential of rhizospheric and endophytic Bacillus species and phyto-antiviral principles against tobacco streak virus in cotton

Plant growth promoting rhizobacteria arewidely exploited for the management of various fungal and bacterial diseases in plants. However, antiviral action of PGPR and their efficiency have been rarely investigated. In the present study, influential diversity of Bacillus species was related with tobacco streak virus (TSV) infection in cotton. The study revealed that, the population of B. subtilis, B. licheniformis and B. velezensis in rhizosphere of apparently healthy cotton plants were comparatively higher than TSV infected plants, indicating that they efficiently colonized the rhizosphere. Similarly, the population of the endophytic B. cereus and B. licheniformis were relatively higher in apparently healthy than TSV infected cotton plants. In vitro screening of rhizospheric, endophytic Bacillus species and phyto-antiviral principles revealed that rhizospheric B. amyloliquefaciens (VB7) and endophytic B. licheniformis (CoEH6) were effective in the suppression of TSV symptoms in indicator host (cowpea). The strain B. amyloliquefaciens (VB7) contained ten antimicrobial peptide genes responsible for the biosynthesis of antibiotics including, iturin, bacilysin, bacillomycin, surfactin, subtilin, and subtilosin. Moreover, the strain VB7 is reported to secrete pentadecenoic acid, heptadecenoic acid, octadecenoicacid, pyrrolo, piperazinedione and tetradecenoic acid, which would have together complemented in the antiviral activity. Upon simultaneous inoculation of the bacterium or phyto-antiviral principles with TSV in the indicator host plant, revealed that B. amyloliquefaciens (VB7) and M. jalapa were much effective and reduced the number of lesions up to 2.22/leaf and 3.00/leaf respectively compared with TSV inoculated control (25.28 lesions cm−2 area). Further, under field conditions, soil application and foliar spray of the B. amyloliquefaciens (VB7) resulted in 52 per cent reduction in TSV incidence. For reference TSV incidence in B. amyloliquefaciens (VB7) treated and untreated plots were 21.67 (PDI) and 45 (PDI) respectively. Moreover, B. amyloliquefaciens (VB7) improved seed cotton yield upto 149.45 g/plant compared to control (97.71 g/plant). Thus B. amyloliquefaciens (VB7) was exploited as an efficient antagonist for the management of TSV in cotton.