Identification And Pyramiding Of Clubroot Resistance Genes In Brassica Rapa L.

Clubroot disease is a kind of worldwide soil borne disease which mainly harms cruciferous crops.In recent years,the occurrence of this disease is increasing in China and leading to serious damage.Breeding disease-resistant varieties is one of the most effective methods for controlling clubroot disease.In this study,some resistant materials were obtained through artificial inoculation identification;Identification of resistant genes was carried out by molecular markers.The materials with different resistance gene were crossed to pyramid resistant genes.QTL-seq technique was used to locate resistant genes from turnip.The main results are as follows:1.An efficient and accurate inoculation identification method was established.Three Plasmodiophora brassicae physiological races from Liaoning,Yunnan and Henan in China were used for artificial inoculation identification of 52 materials by root dipping method and finally 21 materials showed resistance.2.Related literature has reported 22 molecular markers linked to 10 genes against clubroot disease.10 available molecular markers were screened out by preliminary marker screening of 121clubroot disease materials.Comparing the results of inoculation and marker identification of 52materials,the genes CRa and CRc were specifically resistant to Plasmodiophora brassicaeM01 and M02 and the gene Crr3 was specifically resistant to M03.A total of 111 hybrid combinations were constructed by using 22 parental materials.All combinations were identified by molecular markers and finally obtained 45 combinations with two resistant genes,21 combinations with three resistant genes and one combination with four resistant genes.Inoculation identification was performed on 28combinations and obtained 14 disease-resistant combinations;of which 13 combinations showed resistance to Plasmodiophora brassicae M01 and M02,and one combination showed resistance to Plasmodiophora brassicae M01 and M033.The F₂ segregating population was constructed by crossing the European turnip 877 of high clubroot resistance with the Chinese cabbage 255 of high susceptibility.The disease resistance to three Plasmodiophora brassicae was identified on parents,F₁ and F₂ population.The results showed that the disease-resistant parents and the susceptible parents were resistant and susceptible to three Plasmodiophora brassicae,respectively.F1 showed resistance to three Plasmodiophora brassicae.Identification of the disease resistance was carried out on F₂ population and establish an extremely resistant ponl and a susceptible pool.The QTL-seq technique was used to re-sequencing the disease-resistant and susceptible pools and their parents.Through SNP index analysis,two sites related to disease resistance were found on A03 and A08 chromosome.Using SNP sequencing information and Chinese cabbage genome annotation information,we found that 17 non synonymous mutation sites came from 14 candidates,of which three candidate genes were unknown.In summary,this experiment has screened multiple resistant source materials through the inoculation identification method,achieved the pyramiding of multiple resistant genes through hybridization,and used QTL-seq technology to locate the resistant genes in one material.