Discovery Of Resistance Loci To Clubroot(Plasmodiophora Brassicae)in Brassica Rapa

Chinese cabbage is one of the Brassica vegetable crops of the Cruciferous family.It is an important commercial crop of the Cruciferous family.Its cultivated area is very wide in China.Cruciferous clubroot is an obligate parasitic soilborne disease caused by Plasmodiophora brassicae Woron.It is one of the important diseases that harm the yield of Chinese cabbage and other cruciferous crops.Breeding and cultivation of disease-resistant varieties is an effective way to control clubropathy.In this study,a series of researches were carried out on the inoculation technology of Chinese cabbage clubroot at seedling stage,the identification of resistance of Chinese cabbage varieties,and the mining of clubroot resistance genes.The main research results are as follows:The highly susceptible variety of Chinese cabbage’Juxin’was used as the test material,and the clubroot of Beijing Shunyi were selected for inoculation.The injection method and root-dip method were optimized,comparing the effects of different tray specifications,inoculation injection volume,root soaking time and other factors on the effect of inoculation.The results showed that:when using the injection method,the injection volume of 2 m L has a significant effect compared with the injection volume of 1m L,and the disease index is significantly different;when the root system is soaked for more than 5 minutes,there is no significant difference in the disease index.And there is no significant difference in the size of different trays.This experiment is based on the 15 collected in the market.Several disease-resistant varieties were inoculated and identified with pathogens in multiple regions,aiming to understand the resistance performance of different disease-resistant varieties.Using the optimized inoculation method,the rhizocystis in the fields of Nanyang,Henan,Shunyi,Beijing,and Wulong,Chongqing were used as the source of clubroot,and the collected cabbage varieties were artificially inoculated and identified.The results showed that:different cabbage varieties showed inconsistent resistance to bacterial sources from different regions,CR Huimin,CR Limin and Degao CR117 had excellent resistance performance,CR Gao Lengdi and Degao CR117 showed immunity to Beijing Shunyi bacterial source and exist Six disease-resistant varieties showed vertical resistance.Disease resistant varieties were tested for disease resistance genes.CR Fuxing,CR Gaolandi,CR Limin,Gaoyuanlv and Wanqing Kezhonghuang were tested to contain CRa disease resistance genes,and Shengchun varieties were tested to contain Crr1 and CRd disease resistance genes.At the same time,this experiment found that the resistance performance of the variety has a certain correlation with the characteristics of early maturity and sowing type.Previously,the F₂ mapping population derived from a cross between a resistant turnip and a susceptible Chinese cabbage showed that resistance to Pbh（pathotype4）in this population was controlled by multiple genes with complementary effect.Two candidate regionls were found by BSA-seq and located on chromosomes A03 and A08 respectively,named Bcr1 and Bcr2,respectively.In this study,an F_2:3 population including 180 families derived from F₂ individuals were phenotyped and used to verify and narrow candidate regions.A total of 117 pairs of KASP primers were designed every20 Kbp from QTL mapping regions.Ten and six effective markers were screened to construct a linkage map and covered 4.3 Mb-4.78 Mb（A03）and 0.02 Mb-0.79 Mb（A08）,respectively.Phenotypic variation explained（PVE）of the two QTLs were 33.3%and 13.3%respectively.The two QTLs contained 99 and109 genes,covering 480 Kbp on chromosome A03 and 770 Kbp on A08.Bcr1,which Pb Ba3.1（resistant to pathotype 2）located in the same region,had three candidate genes,Bra006630,Bra006631and Bra006632,encode Leucine-rich repeat proteins,and were homologous to the AT5G22670 and AT5G22730 on chromosome Chr5 of Arabidopsis.Bcr2 contains two genes,Bra030815 and Bra030846,which encode Leucine-rich repeat proteins,which are homologous to the AT1G56130 and AT1G55610genes on the Chr1 chromosome of Arabidopsis.