Biocontrol Evaluation Of Bacillus Subtilis Strain AR11 Against Meloidogyne Incognita And Pantoea Agglomerans NJ07 Against Ralstonia Solanacearum

Bacillus subtilis strain AR11 was evaluated for its ability to control the root-knot disease caused by Meloidogyne incognita. Bacterial suspension and the supernatant of fermentation were used for treatment of M. Incognita eggs and the second stage juveniles (J2) in vitroassay. In 12, 24, 36, and 48 hours treatment, 5 times dilution of AR11 bacterial suspension showed the inhibiting efficiencies to J2 as 55.7%, 59.5%, 58.0%, and 47.5% respectively. Hatching percents of eggs were 29.1% and 29.7% higher in 8 days treatment with 10 times dilution of AR11 bacterial suspension and 5 times dilution of AR11 bacterial supernatant than in the control. The greenhouse experiments showed that AR11 could not only promote the growth of tomato plant with 25.6% mass weight increase, but also suppress the formation of the galls and eggmasswhich were 68.2% and 75% less in thetreatment of 10 times dilution of AR11 suspension than in the control group.In the field-greenhouse experiment, the synergic protection of AR11 and agrochemical, termed as JINZHONGLING, of cucumber plants against root-knot disease caused by Meloidogyne spp. was studied. 20% more relative control efficiency was provided by the combination in which soil was firstly fumigated with DUJUNLING 7 days prior to transplanting, and then watering plants with 400 ml of 64 times dilution of AR11 preparation 7 days after transplanting, than by soil fumigation with DUJUNLING only.Bacterial isolate NJ07 identified as Pantoea agglomerans was studied in the greenhouse to explore its roles in controlling bacterial wilt (BW) disease caused by Ralstonia solanacearum. To monitor colonization pattern of the antagonistic bacteria in the rhizosphere of tomato, NJ07 was gfp-labeled by triparental mating. The density of both R. solanacearum B3B and gfp-tagged NJ07 were evaluated by selective culture. Potential effects of inoculums on the indigenous microbial community in the rhizosphere were assessed by molecular fingerprinting. That the low abundance of gfp-tagged NJ07 in the rhizosphere indicated the strain suppressed BW disease probably by priming the tomato plant. DGGE (denaturing gradient gel electrophoresis) profile for bacterial community revealed that the wild type NJ07 dominated in the rhizosphere longer than the gfp-tagged strain. Compared with other two treatments, ca 1 order of magnitude more R. solanacearum was found in the treatment of wild type NJ07 at the last sampling. That may indicated that the pre-colonization of the wide type NJ07 in the rhizosphere of tomato enhanced the activity of R. solanacearum and therefore caused more disease incidence.