Abstract

Background:
Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae is a major disease and a threat to rice production worldwide. Several biological, chemical and genetic control approaches has resulted the improved management of BLB of rice. Recently, biological control using plant growth-promoting bacteria is emerging as potential alternative to chemicals. Therefore, identification and evaluation of new PGP bacteria from native sources is an essential step to determine their plant growth promoting activities.

Objectives
The aim of this work was to isolate and identify the plant growth promoting bacteria from rice phylloplane and rhizosphere that antagonistic to X. oryzae pv.oryzae, the causal agent of BLB of rice for eco-friendly management of the disease.

Methodology
Rice phylloplane and rhizosphere bacteria were isolated from the surface of rice leaves and stem as well as from the soil attached to the roots of rice plants, respectively, by dilution plate technique. The antagonistic activity of these isolated bacteria was determined by dual culture method. The antagonistic bacterial isolates were identified by sequencing of 16SrDNA.Plant growth promoting activities were determined by the production of indole acetic Acid (IAA), siderophore and phosphate solubilization assay. Plant growth promotion was assessed by the determination of root length, shoot length and vigor index.

Key findings
Sixteen bacterial isolates were identified as antagonist to X. oryzae pv. oryzae out of 300 bacterial isolates by dual culture method. The results revealed that the maximum growth inhibition of X. oryzae pv.oryzae was recorded in plate inoculated with BDISOB05P while the minimum growth inhibition was recorded by BDISOB98P and BDISOB272R. The moderate growth inhibition was recorded in BDISOB241P, BDISOB16P, BDISOB306R, BDISOB242P, BDISOB220R, BDISOB04P, BDISOB258R, BDISOB219R, BDISOB221R, BDISOB275R, BDISOB283R and BDISOB61R. The antagonistic bacterial isolates were identified by sequencing of 16SrDNA. The bacterial isolates were identified BDISOB04P as Pseudomonas putida, BDISOB05P as Pseudomonas putida, BDISOB16P as Bacillus sp., BDISOB98P as Stenotrophomonas maltophilia, BDISOB241P as Burkholderia sp., BDISOB242P as Burkholderia gladioli, BDISOB219R as Pseudomonas taiwanensis, BDISOB220R as Serratia sp., BDISOB221R as Pseudomonas sp., BDISOB222R as Pseudomonas plecoglossicida, BDISOB258R as Pseudomonas putida, BDISOB272R as Stenotrophomonas maltophilia, BDISOB275R as Pseudomonas putida , BDISOB283R as Pseudomonas fluorescens and BDISOB306R as Pseudomonas putida. The results of growth promoting determinants revealed that eight antagonistic bacterial isolates were observed to produce Indole acetic acid (IAA), sixteen bacterial isolates were able to produce siderophore and nine bacterial isolates were found to show phosphate solubilizing capability. The results of plant growth promotion showed that these bacterial isolates can increase the root growth, shoot growth and vigor index.

Conclusion
The results conceded some of the PGP bacterial isolates seem potential in both growth inhibition of X. oryzae pv. oryzae and growth promotion of rice plants.

Key words: Identification, plant growth promoting,antagonistic,bacteria,Xanthomonas oryzae pv. oryzae