Plant Growth Promotion and Suppression of Bacterial Leaf Blight in Rice by Inoculated Bacteria

Abstract

The present study was conducted to evaluate the potential of rice rhizosphere associated antagonistic bacteria for growth promotion and disease suppression of bacterial leaf blight (BLB). A total of 811 rhizospheric bacteria were isolated and screened against 3 prevalent strains of BLB pathogen Xanthomonas oryzae pv. oryzae (Xoo) of which five antagonistic bacteria, i.e., Pseudomonas spp. E227, E233, Rh323, Serratia sp. Rh269 and Bacillus sp. Rh219 showed antagonistic potential (zone of inhibition 1–19 mm). Production of siderophores was found to be the common biocontrol determinant and all the strains solubilized inorganic phosphate (82–116 μg mL-1) and produced indole acetic acid (0.48–1.85 mg L-1) in vitro. All antagonistic bacteria were non-pathogenic to rice, and their co-inoculation significantly improved plant health in terms of reduced diseased leaf area (80%), improved shoot length (31%), root length (41%) and plant dry weight (60%) as compared to infected control plants. Furthermore, under pathogen pressure, bacterial inoculation resulted in increased activity of defense related enzymes including phenylalanine ammonia-lyase and polyphenol oxidase, along with 86% increase in peroxidase and 53% increase in catalase enzyme activities in plants inoculated with Pseudomonas sp. Rh323 as well as co-inoculated plants. Bacterial strains showed good colonization potential in the rice rhizosphere up to 21 days after seed inoculation. Application of bacterial consortia in the field resulted in an increase of 31% in grain yield and 10% in straw yield over non-inoculated plots. Although, yield increase was statistically non-significant but was accomplished with overall saving of 20% chemical fertilizers. The study showed that Pseudomonas sp. Rh323 can be used to develop dual-purpose inoculum which can serve not only to suppress BLB but also to promote plant growth in rice.

Biocontrol of Bacterial Leaf Blight of Rice and Profiling of Secondary Metabolites Produced by Rhizospheric Pseudomonas aeruginosa BRp3

“…In vitro plate assay for screening the rhizobacterial isolates (512) for inhibition of growth of Xoo led to the selection of P. aeruginosa BRp3 for further studies. In a previous study, only LB medium was used for isolation of antagonistic bacteria and the frequency of antagonistic bacteria among the total isolated bacterial population was low (Yasmin et al, 2016). A relatively higher number of antagonistic bacteria was obtained in the present study when different growth media (Nutrient Agar, King's B, and Gould's S1) were used for isolation of bacterial populations.…”

“…oryzae (Xoo) strains i.e., Xoo1, Xoo2, Xoo4, Xoo5, Xoo6, and Xoo7 were obtained from NIBGE Biotech Resource Centre (NBRC), Faisalabad (Yasmin et al, 2016). The pathogenicity of Xoo strains was tested by clip inoculation (Kauffman et al, 1973) on three susceptible rice varieties i.e., Super Basmati, Basmati 385, and Basmati 2000.…”

“…Available sequences of bacterial lineage in NCBI were used to align and compare the sequence data using BLAST. Accession numbers were allocated after submitting the sequences to NCBI GenBank database (Yasmin et al, 2016). …”

“…However, again the major emphasis of these previous studies was on the biocontrol activity. Rhizospheric antagonistic Pseudomonas aeruginosa have been documented as beneficial biocontrol agents against Xoo (Yasmin et al, 2016) but the role of diverse secondary metabolites produced by different strains of P. aeruginosa in the suppression of BLB pathogen has not been reported earlier.…”

Understanding and exploiting plant beneficial microbes

“…However, interpreting the effect of microbial (and plant) diversity on microbiome function must be done in a nuanced and context-dependent manner [51]. Complex inocula can provide plants with stronger disease resistance [52–57] and growth promotion [58,59] than single strains. Use of a complex inoculum, rather than single strains, improved arsenic sequestration efficiency of the hyper-accumulator fern Pteris vittata [30], tripling phytoremediation efficiency.…”