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Additional file 1. Table S1. Amount of fertilizer applied per plant. Fig. S1. Colony morphology of isolated bacterial strain Ralstonia solanacearum WS-001 on TTC medium. Fig. S2. Symptoms produced by WS-001on tobacco plant. Fig. S3. Stem streaming test. Fig. S4. Colony morphology of WS-10 on LB medium plates. Fig. S5. Phylogenetic tree constructed for molecular identification of WS-001 and WS-10. Fig. S6. Indole-3-acetic acid production ability of biocontrol agent WS-10. Fig. S7. Co-culture assay.

Lysobacter. spp. are considered as important biocontrol bacteria, due to their antagonistic activity against many pathogenic fungi, bacteria and nematodes. Rep-PCR was used to analyze the genetic diversity of 12 Lysobacter strains. These strains included Lysobacter antibioticus (HY, 13-1, 13-6, 6-B-1, 13-B-1, 6-T'-4, LJ6-3, LJ6-4 and LR9-3), Lysobacter enzymogenes (DH3, 1-T-1-4) and Lysobacter capsici (LG18) isolate from different regions in Yunnan province of China. Rep-PCR was performed using DNA amplification with primers based on short bacterial repetitive elements (ERIC, BOX, IS1113 and J3). The genetic diversity was analyzed through rep-PCR, molecular fingerprint clustering analysis and UPGMA to construct phylogenetic tree. The results show that when the genetic distance was 0.59, IS1113-PCR could cluster the Lysobacter strains as 3 species: L. antibioticus, L. enzymogenes and L. capsici. The 3 species had obvious differences between each other and the rep-PCR technique could be used to detect genetic variation between different Lysobacter strains, identification and strain classification. Key words: Lysobacter, Rep-PCR, genetic diversity.

Lysobacter antibioticus is an important biocontrol bacteria against phytopathogens in soil, and with the ability to produce nonvolatile antimicrobial metabolites has been extensively characterised. It is important to establish applicable techniques to detect and monitor L. antibioticus directly and accurately in soil samples. We developed and tested 13 primer sets according to phenazine gene (phzA, phzB, phzD, phzF, phzS) and the cyclohexanone monooxygenase gene (phzNO1); a pair of primer phzNO1 F1/phzNO1 R1 based on the cyclohexanone monooxygenase (phzNO1) gene of L. antibioticus strain OH13 was selected and optimized polymerase chain reaction (PCR) amplification conditions for rapid and accurate detection. After screening eight strains of L. antibioticus, two strains of Lysobacter enzymogenes, one strain of Lysobacter capsici, Arthrobacterium, Bacillus, Microbacterium, Burkholderia, Pseudomonas and other bacterial strains isolated from different agricultural soils, the phzNO1 F1/phzNO1 R1 primers amplified a single PCR band of about 229 bp from L. antibioticus. The detection sensitivity with primers phzNO1 F1/phzNO1 R1 was 5.14 × 104 fg/25μL of genomic DNA and 2.254 × 1010 to 2.254 × 1011 colony-forming units/mL for the soil samples. Quantitative PCR assays were to develope as a specific method to monitor the L. antibioticus population in soil as well as guide soil micro-ecological management.

Bacterial leaf blight (BB) is a worldwide destructive rice disease caused by pathogen Xanthomonas oryzae pv. oryzae ( Xoo ). A novel strain of Lysobacter antibioticus , which was isolated from the rhizosphere of rice in Yunnan Province of China, can significantly inhibit the growth of various phytopathogenic bacteria and fungi, especially BB pathogen Xoo . In greenhouse experiments, whole bacterial broth culture (WBC) of strain 13-1 was more effective in reducing BB than other components of the culture, with disease suppression efficiency up to 69.7%. However, bacterial cells re-suspended in water, cell-free culture extracts, and heated cultures also significantly reduced BB severity. Suppression efficiencies ranged from 79.0% to 61.8% for undiluted to 100-fold dilution treatments and from 57.6% to 31.7% when the WBC of strain 13-1 (10 8 CFU/mL) was applied at 3 days and 7 days prior to pathogen inoculation, respectively. In three field trials, strain 13-1 reduced BB incidence by 73.5%, 78.3%, and 59.1%, respectively. Disease suppression by strain 13-1 varied significantly among different rice cultivars, although efficacy was not directly related to the susceptibility level of the cultivars. Efficacy of biocontrol was also affected by different pathogen isolates, with some isolates of Xoo being more sensitive to 13-1 suppression than others. These results suggest that antibiotics and density of colonization on leaves may be involved for biological control of rice BB by strain 13-1. To our knowledge, this is the first report of L. antibioticus being a potential biocontrol agent for rice bacterial blight.