[Screening, identification and optimization of fermentation conditions of an antagonistic endophyte to mulberry...

Antagonistic endophytic strains with strongly inhibitory activity to mulberry bacterial blight (P. syringae pv. mori) were isolated from mulberry endophytes, we identified the antagonistic endophyte and optimized the fermentation conditions.

Streak plate method was used to separate the endophytes from healthy mulberry tissues after strict surface disinfection. Antagonistic endophytes were screened out through inhibition zone method. Strain SWg2 was identified by morphological, physiological and biochemical characteristics and 16S rDNA sequence analysis. The conditions of fermentation and medium composition were optimized through single factor and orthogonal experiment.

In total 77 endophytic strains have been isolated from healthy mulberry. SWg2 showed strong and stable antagonistic activity to mulberry bacterial blight. The morphological, cultural, physiological, and biochemical characteristics assays indicated that SWg2 belongs to Pantoea sp. The 16S rDNA sequence phylogenetic analysis reveals that SWg2 appeared a sister lineage to P. agglomerans. The optimized culture conditions of strain SWg2 were liquid volume 20 mL in 100 mL flask, 170 r/min at 28 degrees C, inoculation size of 4% for 5 d with a medium of 2.0% glycerol, 2.0% NH4NO3, 0.1% KH2PO4, 0.15% MgSO4 x 7H2O at initial pH of 7.5.

The antagonistic endophytic strain SWg2 to mulberry bacterial blight was identified as P. agglomerans. SWg2 strain shows stronger antagonistic action to mulberry bacterial blight under optimized fermentation conditions.