Selection And Application Of Clubroot Resistance Germplasm In Cruciferous

Clubroot is a new type of soil disease caused by Plasmodiophora brassica Woronin,resulting in swelling and decay of the roots,which in turn causes a reduction in the production of Cruciferae crops and seriously endangers the growth of Cruciferae crops.Many researchers have shown that the chemical and agricultural methods to control clubroot disease have little success.Screening for resistant germplasm materials,creating resistant germplasm,and planting resistant varieties are the effective ways to control clubroot disease.When plants are affected by external pathogenic bacteria,a series of disease resistance mechanisms are produced through their own defense mechanisms to protect them from invasion..Some researchers studied the mechanism of clubroot disease by analyzing the changes of physiological indexes between resistant and susceptible materials,providing theoretical basis for disease resistance breeding of Cruciferae.This experiment mainly consisted of screening of resistant materials,creation of resistant germplasm,analysis of the changes of physiological indexes between the resistant and susceptible materials,and the expression of genes related to clubroot resistance.The main research results are as follows:1.The 97 Cruciferous materials were inoculated using the pathogen collected in Taibai County,Shaanxi Province,and the level of resistance was counted to calculate the incidence rate and disease index.The results showed that the incidence rate and disease index of different materials were very significant.The incidence rate was significantly related to the disease index.As a result,15 high-resistance materials,8 resistant materials,5 sensitive materials,and 69 high-sensitivity materials were identified from 97 Cruciferous materials.The results of resistance classification were basically consistent with those of European cluster analysis.Thirty-nine materials with significant differences in resistance in the above materials were selected and inoculated using the pathogen in Mian County,Shaanxi Province,it was showed that the difference between the incidence rate and the disease index was very significant,and three high resistance germplasms,W1,W3 and W4were identified,which were resistant to the two different pathtypes from Taibai and Mian counties.2.Eleven backbone parents of Brassica napus such as 1921,1920 were used as female parents,the high resistance materials W1?clubroot resistance 518,Chinese cabbage?and Laurentian?turnip?screened by the above experiments are the male parents.The resistant hybrid F₁ was obtained by distant hybridization combined with embryo rescue technology.The morphological identification,cytological identification,SSR molecular marker identification were used to identify the obtained hybrid F₁ as a true hybrid.Among them,there were 5 false hybrids and 50 real hybrids in the 55 selected embryo rescue plant seedlings,and their true hybrid rate was 90.91%;Among the 55 field hybrids selected,there were 7 false hybrids and 48 real hybrids.The true hybrid rate was 87.27%.3.Thirty-nine cruciferous materials with different resistance were inoculated by the pathogen collected in Taibai County,Shaanxi Province.The contents of soluble protein,chlorophyll,proline and malondialdehyde in leaves of 7,14 and 28 days after inoculation were determined,and the correlation and variation of each index were analyzed.It was found that the four indexes reached a peak in 14 days after inoculation,and the soluble protein was significantly positive correlated with the disease index.The malondialdehyde content was significantly positive correlated with the disease index in 28 days after inoculation,and the proline content in three periods was extremely significant,and showed a negative correlation with the disease index.4.From the above tests,the two Chinese cabbage materials W1 and Z1 with significant differences in resistance were selected,and four genes Bra012540,Bra012541,Bra012581and Bra012571 with TNL?TIR-NBS-LRR?structure were selected from the A03chromosome.RT-qPCR technology was used to analyze the relative expression of of these genes in roots and leaves of 14 days after inoculation.The results showed that the candidate genes showed different expression patterns in leaves and roots of resistant and susceptible materials,and the expression difference of Bra012581 in the resistant and susceptible materials reached a very significant level.Therefore,this gene was initially selected as a candidate resistance gene for future follow-up studies.