Screening And Mutation Breeding Of Antagonistic Strains Against Plasmodiophora Brassicae

Clubroot that caused by Plasmodiophora brassicae is one of the most serious soil-borne plant diseases all over the world. This disease usually harms cruciferous vegetables and infects plant roots causing severe root rot and even the whole plant die. At present, there is no effective way to control clubroot at home and abroad. The control efficiencies of chemical control are unstable, and chemical control easily causes resistant, environmental pollution. Although disease-resisted breeding is effective, there are no resistant materials for most oilseed crops and cruciferous vegetables. The purpose of this study is obtaining antagonistic strains against P. brassicae, so we isolated and screened antagonistic strains from rhizosphere soil, root, stem and twigs of cruciferous vegetables, two antagonistic actinomycetes strains were filtered out by measuring the dormant spore germination rate of P. brassicae.We identified and mutated this two antagonistic actinomycete strains,then we obtained two mutant strains whose antagonist function were better by ultraviolet, Diethyll sulfate (DES) and complex mutagenic method. The control efficiencies of this two antagonistic actinomycete strains and the two mutant strains against clubroot were evaluated by the control effect of pot experiments and field experiments. The main results are listed as follows:1.Isolation and screening of antagonistic strains We isolated152strains of bacteria,110strains of actinomycete,63strains of fungi from rhizosphere soil, root, stem and twigs of cruciferous vegetables in the experiment.9antagonistic strains were filtered out by measuring inhibition rate of dormant spores of P. brassicae. We also studied the control efficiencies of9antagonistic strains against clubroot in pot experiment. From these9strains, antagonistic actinomycete strains F-22and F-24were filtered out finally.2. Identification of antagonistic actinomycetes Antagonistic strains F-22and F-24were identified by traditional classification and molecular classification. There were no closely related sequences from GenBank database between F-22and F-24.But according to their morphological traits, cultural traits, and physio-biochemical characteristics,F-22was affiliated to Cinereus of Streptomyces and F-24was affiliated to Globisporus of Streptomyces. Deposited the nucleotide sequences of F-22and F-24in the GenBank database, their accession numbers were JQ863115and JQ863116.3. Mutation breeding of antagonistic strains F-22and F-24Antagonistic strains F-22and F-24were mutated by ultraviolet, Diethyll sulfate (DES) and complex mutagenic method of ultraviolet and DES. The mutation effects to F-22and F-24of this three mutagenic method were studied, ultraviolet was the optimal mutagen of F-22and F-24.Screening the mutant strains,two mutant strains F-22-29and F-24-8were screened out whose inhibition rate of dormant spores of P.brassicae reached85.64%,82.34%.Compared with the original strains F-22and F-24,the inhibition rate of dormant spores of P.brassicae of F-22-29and F-24-8increased51.74%,29.71%.The inhibition rates of dormant spores of F-22-29and F-24-8didn’t change for10generations. The genetic stability test proved that F-22-29and F-24-8had good genetic stability.4. The control effect of pot experiments and field experiments The result shows that:The control efficiencies of antagonistic actinomycete strains F-22and F-24against clubroot in field experiment were46.39%,48.14%while the control efficiencies of mutant strains F-22-29and F-24-8were59.99%、58.93%. The control efficiencies of mutant strains were higher than listed chemicals and biological pesticides.The study proves that mutant strains F-22-29and F-24-8had high development potential.