Studies On Fusarium Oxysporum Toxin And Its Effects On Soybean Root

Soybean root rot was caused by several pathogens. The results showed that there were 7 pathogens, Among them, F. oxyspontm can be isolated with highest frequency, and it' s a main pathogen.PD liquid medium was suitable for F.oxysporum growth and PSC liquid medium was the best for the toxin production. The optimum culture condition for F.oxysporum growth was at 20~30 , pH6~7, darkness, and toxin production of F. oxysporum was 25~30癈, 15d, light, continuous shock; and pH was no significant effect on toxin production.F.oxysporum toxin solution could be harmful to seedling root of soybean. The symptoms of the toxin inducing lesion on soybean root were similar to the symptoms caused by the pathogen after inoculation , the results showed toxin could inhibit activity of soybean root , the higher the conductivity of cell membrane was, the bigger the lesion was.After soybean roots were inoculated by toxin, the protein content of resistant variety decreased and the protein content in young root of susceptible variety increased within 6h after treatment, after 12h, the protein content of the two varieties were decreased rapidly, the content of glucose decreased rapidly in two varieties, too. The content of proline were increased significantly and it was much higher in susceptible variety than in resistant one. The result also showed that the changes in activities of PAL, POD and PPO in cell were similar. All of them were increased rapidly at the beginning of treatment, then they were decreased later. The peak of PAL, POD and PPO activity in resistant variety appeared later than it in susceptible one, but the activities of them in resistant variety was showed a higher level.Ultrastructural study were made of the soybean radicles of resistant variety and susceptible variety exposed to toxin, produced by F. oxysporum, at 25% and 70% concentrations. A series of subcellular changes were observed, including the transformation and disruption of cell wall, the plasmolysis, the disruption of mitochondria, plasmalemma, nuclei and vacuolar membrane, the swollen and transformation of chondriosome, the transpar ency of internal matrix, the disruption of some cells. The mitochondria crista and plasmalemma, the damageson membrane systems of the cells in the resistant variety are lighter and than the susceptible one.It was significant different that culture filtrates are harmful to radicles. Growth of radicles was slower in susceptible variety than the resistant one. When Difference was more bigger between resistant and susceptible varieties , difference of conductivity was also significant change. It was possible that culture filtrate was used to identify resistivity of soybean varieties to root rot.