Identification Of Clubroot Pathogen On Cabbage And Screening Of Resistant Germplasm Resources

Cabbage clubroot disease,is a soil-borne disease,severe damage,which was recorded as early as thirteenth century,the pathogen was first discovered in 1878,and named Plasmodiophora brassicae Woronin by the Russian scholar Woronin. The disease was distributed in the whole world,and in rencent years,it become more and more serious in our country,The selection of resistant materials screening and disease resistant varieties has become an urgent problem to be solved.In 2013 September,the Cabbage Breeding Laboratory of Northeast Agricultural University found a disease to be suspected of cabbage clubroot in the cabbage breeding test ground,because the disease has not been reported in Harbin in previously,so in this study,starting from the pathogen identification of the disease,taking a combination means of traditional morphological taxonomy and ITS sequences alinment methods in molecular biology,and then study the biological characteristics of the cabbage clubroot pathogen;on the basis of this,screening of a set of convenient and shortcut methods for identification of resistance to cabbage clubroot disease of cabbage at seedling stage;20 cabbage breeding materials were identificated for seedling resistance to cabbage clubroot disease. It has laid a solid theoretical and practical basis for future cabbage resistance to cabbage clubroot disease breeding work, the main findings are as follows:(1) The pathogen causing clubroot on cabbage in Harbin area was identified in this study,by morphological observation and pathogenicity testing,preliminary suspect this disease is caused by Plasmodiophora brassicae Woron. Then by using of conservation and variability of the internal transcribed spacer(ITS) of Plasmodiophora ribosome DNA, the sequence was analyzed by comparing with that in Gen Bank. The molecular identification indicated the same results with morphology identification.(2) We have defined the basic biological characteristics of Plasmodiophora brassicae: Treatment of rotted clubs was helpful to enhance the germinated rate, freezing treated on the resting spores’ s germination has little impact;The highest germinated rate for the resting spores was in the root exudates the optimum p H was 6.0. the optimum temperature for the germination of resting spores was 24℃The visible light inhibited the germination of the resting spores,The thermal death point of he resting spores was 44℃.(3) To screen the optimum system for Plasmodiophora brassicae inoculation,different inoculation methods as well as the spores concentration and soil p H conditions were compared in this study.the trial filtered out the optimum method:the optimal inoculation method was mixing resting spores of the pathogen with soil,inoculum concentration for 1.6×108 spores/per gram substratum,the optimum soil p H is 6.0.(4) The artificial inoculation identification method was applied on the 20 cabbage breeding materials of cabbage to identificate the seedling resistance to cabbage clubroot,3 resistant(R) materials,9 middle resistant(MR)materials,7 susceptible(S) materials,and 1highly susceptible(HS) material.