The Analysis Of Processing Tomato Root Rot Disease Occurring Reason And Study Of Control Mechanism Of Biocontrol Bacterial Under-mulch-drip Irrigation In Xinjiang

Root rot diseases are the most severe diseases of tomato for preserving food in XinJiang province.No effective control method for this disease has been developed due to soilborne of the pathogens and prohibition of chemical pesticide use.In this thesis, morphological and molecular biology methods were used to identity pathogens of the disease;microbial communities in the rhizosphere of the tomato plants with different severity of Pythium root rot were assessed including plate counting method,soil enzyme activities,and changes in community structure(denaturing gradient gel electrophoresis(DGGE)analysis).The bacterial biocontrol agents were isolated and identified,which could not only control the root rot diseases,but also promote growth of the tomato plants.Their mechanisms for control of the disease were studied.The results are valuable to build up biocontrol theory and technique for management of the tomato root rot disease in XinJiang.The major results of this study are as follows:One hundred sixty-two root rot diseased tomato plant samples were collected from XinJiang and 120 isolates were obtained.Ninety-three of them were Pythium isolates, which was 77.5%of the total based on morphological and molecular biological tests, which were identified as Pythium aphanidermatum(Edson)Fitzp(56 strains,60.22%of all Pythium isolates),Pythium monospermum Pringsheim(6 strains,6.45%of all Pythium isolates)and Pythium acouldthicum Drechsler(2 strains,2.15%of all Pythium isolates).Other 29 strains could not be identified due to no oogonium and sporangia.Microbial communities in rhizosphere of the tomato plants with different severity of Pythium root rot were assessed including plate counting,soil enzyme activities, FAME analysis,and denaturing gradient gel electrophoresis(DGGE)analysis for community structure.The results showed that the population of bacteria and actinomycetes were highest in the rhizosphere of health tomato plants,intermediate in the diseased,and lowest in the dead.In contrast,fungi population was highest in rhizosphere of death tomato plants,intermediate in the diseased and lowest in the healthy in two different plots and different tomato grown stage.FAME analysis and DGGE analysis also proved that there was more complicated community diversity in the healthy tomato rhizosphere soil.The data also showed that except cellulose, hydrogen peroxidase,urease,invertase,phosphorylase proteinase were highest in rhizosphere of the healthy tomato plants,intermediate in the diseased,and lowest in the dead in different tomato grown stages.All the results confirm that plant health is closely related with soil health which is free of the root rot pathogens.Eight hundred forty-two bacterial strains and 187 actinomycetes strains were isolated from rhizosphere soil of the tomato plants from different areas of XinJiang. After repetitive co-culture on PDA plates,54 bacterial strains were screened for their stable antagonism against P.aphanidermatum,R.solani,F.oxysporum f.sp.lycopersici, P.capsici,A.solani and S.sclerotiorum and followed by germination,pot,small plot and field tests.The best antagonistic bacterium S37 and S44 were selected,which could promote germination and growth of the tomato plants,control the plant diseases effectively and increase yield of the tomato.They were identified as Bacillus subtilis based on morphological,physiological,biochemistry and molecular biological tests.The mechanisms of biocontrol agents the pythium root rot pathogens were studied based on the plant physiology,biochemistry,soil biology and soil microbial ecology methods.The result-showed that S37 and S44 could maintain seed vigor,promote seed germination,induce enzymes,such as peroxidase,polyphenol oxidase and superoxide dismutase related with the disease resistance.Most effective control of the disease was achieved after seed dressing and drip irrigation of the biocontrol agents in rhizosphere of tomato plants for 2 times.It improved cellulose,hydrogen peroxidase,urease, invertase,phosphorylase proteinase activity,soil microbial biomass carbon,microbial biomass nitrogen and microbial biomass phosphorus and microbial community diversity in rhizosphere of the tomato plants.It also regulated microbial community diversity, improved soil quality.However,poor biocontrol effectiveness and less microbial biomass and diversity was noted when drip irrigation of the biocontrol agents in the rhizosphere for 3 times.Fungicide Metalaxyl could effectively control the disease,but it reduced soil enzyme activity,soil microbial biomass and microbial diversity.It resulted in soil quality reduced.