And From Plant Rhizosphere Bacteria Screening And Its Effect On Tomato Bacterial Wilt Of Bio-control

Tomato bacterial wilt, a worldwide soil-borne disease, is caused by Ralstonia solanacearum(Pseudomonas solanacearum). This is one of the important diseases in Solanaceae vegetables widely distributed in tropical and subtropical and certain temperate regions. When tomato is infected, leaf is not changed in color, but becomes wilted. In China, incidence rate of this disease varied from5%to85%depending on year, leading to significant economic losses. Breeding disease-resistant varieties and improved culture practices are the measures to bring the disease under control. Application of biological agents is also an option that has attracted more and more attention because they are environmentally friendly. Plant growth promoting rhizobacteria (PGPRs) are sources of biological agents, which colonize plant rhizosphere and confer beneficial effects, such as increased plant growth and reduced susceptibility to diseases caused by plant pathogenic fungi, bacteria, viruses and nematodes by producing antibiotics or inducing expression of pathogenesis-related protein and so on. Present work screened PGPR from different rhizosphere soils and tried to use it in pots. The results showed as follows:(1) Fourteen strains were isolated from different rhizosphere soils sampled from Yangzhou and Yancheng, Jiangsu province. These strains showed in vitro antibacterial effects, the ability to produce NH3, IAA, HCN and siderphore. They also showed ability to dissolve phosphorus and potassium, to fix nitrogen and to promote plant growth. Seven of these strains are Pseudomonas sps, three are Paenibacillus sps, two are Bacillus sps., one is Burkholderia and one is Erwinia, according to their16S rRNA sequences.(2) PGPR strains WP8and RA2exhibited a promising effect in biological control of tomato bacterial wilt caused by R. solanacearum QL-Rs1115, as evidenced by increasing the germination rate, decreasing disease incidence and increasing the accumulation of plant dry matter. Using RA2and WP8as seed soaking agents, tomato germination rate were92.5%and90.4%respectively, significantly higher than that of control (60.4%).Two inoculation methods were compared. Results showed that seed-soakingwas more effective than soil drench. Application of WP8and RA2slightly changed the rhizosphere bacterial community as evidenced by DGGE profiling, implying that using PGPR is an eco-friendly approach to tomato growth against bacterial wilt.Present study demonstrated that biocontrol effects could be achieved if suitable PGPR strains with appropriate inoculation method are applied. The changes of microbial community in rhizosphere caused by application of WP8and RA2strains need to be further studied.