Screening Trichoderma Spp.for Biocontrol Against Soybean Root-rot Pathogen And Study On Biocontrol Mechanisms Empolyed By Trichoderma Spp.

153 isolates of Trichoderma spp. isolated from soybean rotation plots of Hailun ecology research of Chinese Academy of Scinences were assessed in vitro and in vivo to screen for biocontrol agents against soybean root-rot .Three isolates (MM35,MM9,MM3) were isolated with relatively better biocontrol efficacy ,the reduction in root rot were 26.95%～66.34%,21.52%～63.70%,22.78%～51.05%,respectively. Trichoderma MM35,MM9,MM3 all could parasite the mycelium of pathogenic fungi Rhizoctonia solani,light micrographic observation show that none of Trichoderma MM35,MM9,MM3 has the capacity to parasite the propagules of pathogenic fungi F.oxysporum.The dried mycelium of pathogenic fungi Fusarium oxysporum as sole carbon source can induce Trichoderma MM35 to produce chitinase and β-1,3-glucanase . The producton of β-1,3-glucanase by Trichoderma MM35 is induced prior to that of chitinase. Both chitinase and β-1,3-glucanase can be found in the soil inoculated with Trichoderma spp.,F.oxysporum,R.solan,respectively.Activity of chitinase in the soil present of pathogenic fungi Fusarium oxysporum can be significantly elevated when Trichoderma spp. was inoculated ,while there was no significant change in β-1,3-glucanase activity. Activities of β-1,3-glucanase and chitinase in the soil present of pathogenic fungi R.solani both were significantly elevated when Trichoderma spp. was inoculated. F.oxysporum exhibit a higher rate of using glucose compared to Trichoderma spp.,the only exception being F.oxysporum compared to TrichodermaMM9,which show no significant differences. Trichoderma spp.use glucose with higher rate than that of pathogenic fungi Rhizoctonia solani. The only exception being Rhizoctonia solani compared to TrichodermaMM35,which show no significant differences.Some Trichoderma exhibit a higher rate of using HPO42- compared to pathogenic fungi F.oxysporum,while the others show no significant differences in the rate of using HPO42- compared to pathogenic fungus F.oxysporum, R.solani. F.oxysporum and R.solani use Fe+2 with higher rate than Trichoderma spp..The trend was reversed for the pairs Trichoderma MM35- F.oxysporum or Trichoderma MM35- R.solani.The population change of the treatment with presence of Trichoderma was consistent with the control.The trend of population increased first , then decreased with time . The population numbers of pathogenic fungi F.oxysporum of the treament decline to different extents compared to those of the control.The presence of Trichoderma can reduce the number of population of pathogenic fungi F.oxysporum.All the Trichoderma strains did not affect the fresh weight of soybean plants. Only TrichodermaMM9 can increase the dried weight of soybean plants,while the others can not affect the dried weight of soybean. Pathogenic fungi F.oxysporum can reduce both the fresh and dried weight of soybean plants. There were no significant changes in the activity of β-1,3-glucanase and PPO during plant-fungus interactions.Peroxidase activity of the roots treated by Trichoderma peaked at 72h,then decreased gradually with time,whereas Peroxidase activity remained constant with time in none treated plants.Candidate Post Graduate:Shao Hongtao Major:Plant Pathology Supervisor: Prof.Xu Yanli...