A Study On The Anti-predator Effect And Controlling Of Plant Pathogenic Nematodes By Rhizosphere Bacterium

Nematodes are one of the largest species of animals, which is widely distributed in earth, water resources and living organisms. Free-living nematodes and plant parasitic nematodes are the two main kinds of soil nematodes, both of which are fairly abundant in rhizosphere, thus sharing a complex interaction with rhizosphere bacterium. Biological fertilizer has drew increasing attention among these years. Biological fertilizer using rhizosphere bacterium as the main active ingredient has the advantage of multi-efficient, environmental-friendly and long-time sustainable. But in practical application, however, there may often turn out to be many problems. Free-living nematodes, as bacterium predators, which may consume lots of the biocontrol strains, can largely affect the result of bacterium fertilizers, but can also help spread the bacterium and expand its distribution in some occasions. Plant parasitic nematodes, on the other hand, is a kind of pathogenic nematodes that affects the health of crops and horticultural plants. There have been studies abroad focused on the interaction between free-living nematodes and rhizosphere bacterium, while domestic reports are rarely found. Studies on the controlling of plant parasitic nematodes using rhizosphere bacterium has gain achievements both home and abroad. Combining of these two studies, however are seldom seen world-wide.In this study, 14 strains of bacterium were isolated from tomato rhizosphere and compared with present strains in laboratory. Two strains of anti-predator ability against Caenorhabditis elegans were obtained, which are Pseudomonas aurantiaca JD37 and Pseudomonas fluorescens P13. Death rate of C. elegans in slow killing assay driven by these two strains was 26.12% and 18.66%, separately. Compared with Escherichia coli OP50, C. elegans rejected JD37, while prefered P13. Choice index of JD37 and P13 were-0.59 and 0.47, separately. After 7 days of co-culturing, C. elegans with JD37 showed a decreased reproductive capacity, while most of the worms dead were. C. elegans with P13 showed a slightly decrease in activity, and their reproduction is hardly affected. Picrate paper test showed that P. fluorescens P13 had the ability to produce HCN, while P. aurantiaca JD37 had not. Through molecular cloning of PCR, neither JD37 nor P13 had the ability of producing 2,4-DAPG. In this study, we detected the properties of soil from Yanjin District of Xinxiang City in Henan Province, where root-knot nematodes were widely spread on tomato fields. The soil was detected to be neutral in p H, with a relatively high concentration of solute salt. Type of the soil can be roughly judged to be loam or clay loam. The test on irrigation amount showed that in present laboratory condition, root-knot nematodes may infect the tomatoes when water content is under 15 m L/100 g soil/week. Meanwhile, if the irrigation surpass this level, they growth of tomato plants may also be infected. Green house trail showed that both JD37 and P13 can suppress the infection of root-knot nematodes, with P13 strain showed a better effect than JD37.P13 and JD37 strains reduced the number of root-knots by 49.10% and 43.53%, separately, compared with the control group, and promoted the stem growth by 26.41%and 30.26%.These results showed that Pseudomonas aurantiaca JD37 and Pseudomonas fluorescens P13 evolved different mechanism faced with the pressure from predators. P. aurantiaca JD37 is more capable of defending itself from predators, and showed an ability to suppress plant parasitic nematodes as well. P. fluorescens P13, on the other hand, may tend to take use of the free-living nematodes to spread itself among soil, and showed a stronger ability to suppress plant parasitic nematodes compared with JD37. These results enriched our understanding on the interaction between free-living nematodes and rhizosphere bacterium, and provided reference and basis for the study and development of multi-efficient biological fertilizer with the ability of plant-growth promotion as well as plant disease suppression.