Preliminary Study On ZB-6, An Endophytic Bacterial Strain From Tomatoes

A number of endophytic culturable bacterial strains were obtained from roots, stems and leaves of tomato plants by plate culture during 2002-2004. Among all culturable endophytic bacterial strains, ZB-6, a strain from tomato leaf, showed the strongest inhibitory activity to plant fungal pathogens. Main attention was paid to taxonomy of ZB-6, colonization and movement of strain ZB-6 in tomato plants. Inhibition of the filtrate from ZB-6 was evaluated systematically. Meanwhile, control effects of ZB-6 on tomato bacterial wilt (Ralstonia solanacearum) were assessed. The main results are as follows:1. There are a large number of endophytic bacteria in tomato plants. With the surface sterilized with 0.1% mercuric chloride, culturable endophytic bacteria were counted by plate culture. The results showed that culturable endophytic bacteria in tomato plants ranged from 1.78?03 to 2.75?04 CFU (colony formation unit) per gram (FW) . There are more culturable endophytic bacteria in roots than in stems and leaves.2. The endophytic bacteria from tomato plants were with strong inhibition to fungal phytopathogens. Among the total of 93 endophytic bacteria isolates tested, 38, or 40.86%, had in vitro inhibitory activity to fungal phytopathogens, such as Colletotrichum dematium and Alternaria solani,etc. and 12 isolates had in vitro inhibitory activity to Ralstonia solanacearum. The strain ZB-6, isolated from tomato leaf, was with the strongest inhibitory activity.3. The strain ZB-6 was identified as Bacillus subtilis, based on the taxonomic results including cell shape, Gram's stain, sporulation, production of catalase and oxidase ect.34. The strain ZB-6 was able to colonize successfully and move frequently between different parts in tomato plants. ZB-6Rif500, the mutant strain of ZB-6, was resistant to rifampicin. After inoculated with ZB-6Rif500 by spraying leaves and watering roots, a number of ZB0 were found in all parts of tomato plants at 35d after inoculation. The results implied that ZB-6 was able to colonize successfully in tomato and move frequently between different parts of plants.5. Filtrate from ZB-6 cultivation in medium gave strong inhibition to the fungal phytopathogens tested. However, there was obvious difference in inhibitory activity to various fungal phytopathogens. The deformation and disintegration of the spore germinal tube from Alternaria solani were observed 24h after treatment with the filtrate.6. The strain ZB-6 showed effective control to tomato bacterial wilt (Ralstonia solanacearum) in both outdoor pots and field. The control effects of ZB-6 on tomato bacterial wilt were 63.7% at 7d and 58.0% at 27d, respectively in outdoor experiments. Preventive inoculation of strain ZB-6 improved greatly its control effect to tomato bacterial wilt.