Suppressive Soil Of Soybean Cyst Nematode And Suppressive Factors

Soybean cyst nematode (Heterodera glycines Ichinohe) was one of the most important soil borne pathogens of soybean. Because of the many ways of the spread and the worst harm, it was a major yield-limiting factor in the soybean producing. So soybean continuous cropping would accumulate the cysts in soil, resulting in increased the harm of soybean cyst nematode. Recently, some studies reported that in more than five years of soybean continuous cropping soybean fields, the abundance and the damage of soybean cyst nematode population have decreased. This phenomenon was called the decline of soybean cyst nematode, and the soil was called soybean cyst nematode suppressive soil. The soil of long term experiment field was the soybean cyst nematode suppression soil in National Observation station of Hailun Agroecology System, Chinese Academy of Sciences for21years soybean monoculture. Aim to discuss the mechanism of the soybean cyst nematode suppressive soil, the soil of long term experiment field was test. Pot test was done and parasite funguses of soybean cyst nematode were isolated, the strain of high isolate frequency was identified under microscope. The method of Real-timePCR was used to quantify the major parasite fungi. The major bio-control fungi were defined in this research, decline mechanism of SCN suppression soil was also revealed. A new approach was provided for SCN management by natural enemies, it had important academy value and practical significance on the research of nematode ecology.Through the research we found that the densities was significant decline in soybean monoculture for21years.There were just7cysts in every100gram soil and the rate of empty cyst was46%. Eggs and J2were respectively192and26in every100g soil. It was proved that this soybean monoculture field was soybean cyst nematode suppressive soil.We added streptomycin sulfate and pimaricin in the soil of soybean monoculture for21years. At the phenomenon of without inoculated nematode, result showed that the fungi could promote the growth of soybean. By the investigation of the soybean cyst nematode population densities, we found that in sterilization treatment the nematode population densities were fast increase. It proved that the suppression cause was biology factors in this soybean cyst nematode suppressive soil. In addition, fungi were the major bio-control factor, and bacterium was second.The parasite funguses was isolated from soil and soybean cyst nematode in21years soybean monoculture,3years soybean monoculture and wheat/corn/soybean rotation. Except Fusarium spp., in21years soybean monoculture the isolate frequency of Verticillium spp. and Paecilomyces spp.were higher than the other two treatments. It proved that Verticillium spp. and Paecilomyces spp. were the major bio-control fungi in this soybean cyst nematode suppressive soil. The result of identify the strein with hight isolate frequency showed that they were F. oxysporum, V. chlamydosporia, F. redoles, F.equiseti and P. lilacinus. The isolate frequency of V. chlamydosporia is the hightest. It proves that V. chlamydosporia might be the major suppressive fungi in this soybean cyst nematode suppressive soil.Use the method of Real-time PCR to quantify the V. chlamydosporia in the soil of21years soybean monoculture,3years soybean monoculture and wheat/corn/soybean rotation. In21years soybean monoculture, the genetic DNA of V. chlamydosporia was180pg·g-1. It was higher than the other two treatments. It sufficiently proved that the important bio-control fungi were V. chlamydosporia in this soybean cyst nematode suppressive soil.