Crop rotational effects on rhizospheric bacterial community and vascular bacterial wilt disease suppressiveness

Abstract

Abstract The management of Ralstonia solanacearum, incitant of vascular bacterial wilt (VBW) is still a challenging task due to its high degree of genetic diversity, wide adaptability, inefficacy of antibiotics against it under field conditions and temperature dependent resistance breakdown. The present investigation was aimed to identify suitable crops suppressive to R. solanacearum and assess their potential in developing a promising suppressive crop rotation system. Among the 30 treatments with various crops selected based on survey and farmers’ perspective, significant reduction of VBW incidence was observed in sick plot over initial per cent disease incidence (PDI) in the two years successive crop rotations for maize-maize-brinjal (73.91%) followed by sorghum-maize-brinjal (65%), okra-okra-brinjal (65%), okra-maize-brinjal (57.14%) and maize-okra-brinjal (47.62%). Illumina sequencing of the V3-V4 regions of 16S rDNA sequence of rhizospheric soil DNA showed a trend of increase in population of the phyla Firmicutes and Actinobacteria in the rhizospheric bacterial community of the suppressive crop rotations viz., maize-maize-brinjal (MMB), okra-okra-brinjal (OOB) and sorghum-maize-brinjal (SMB). Increase in the populations of Bacillaceae, Burkhloderiaceae, Paenibacillaceae and Strepotomycetaceae were observed at the family level. Further, presence of various biological control agents of R. solanacearum, viz., Streptomyces sp., Burkholderia-Paraburkholderia sp., Bacillus sp., Paenibacillus sp., Stenotrophomonas sp. and Acinetobacter sp. were increased in the rhizosphere of brinjal at the end of two consecutive years of crop rotations of MMB, OOB and SMB. Thus, maize, okra and sorghum were identified to reduce the inoculum load of the soil borne phytopathogen R. solanacearum in sick soil along with delaying and reducing the severity of the VBW incidence when incorporated in the crop rotations.