Mapping Of QTLs For Resistance To Southern Corn Rust In Maize And Resistance Gene Enrichment And Sequencing

Maize(Zea mays L.)is one of the most important cereal plants in the word because of it’s great demands of food,feeding and industrial applying,and plays an important role in China’s agricultural production.The occurrence of pests and diseases can always affect corn yield and quality.Southern corn rust(SCR)is a prevalent foliar disease in maize in China’s main corn producing areas.In recent years,due to climate change and evolution of pathogen,the incidence of southern corn rust in maize has been increasing year by year in China,which has brought great harm to the production of corn.Maize disease resistance breeding and resistance donor selection to SCR is an effective way to control SCR.The genetic research of resistance to southern corn rust can provide a theoretical guidance for breeding of resistant varieties.In the present study,two inbred lines CML496 and P178 were selected as diseaseresistant parents,and the susceptible inbred line Lx9801 was used as a susceptible parent.Two linkage groups were constructed to map the southern corn rust resistance locus.The results are as follows:1.The fist genetic mapping population comprising 139 F5:6 recombinant inbred lines(RILs),developed by single-seed descent from the BC2 population:(CML496 × Lx9801)× Lx9801,was planted in the experimental field for phenotyping at Xuchang in Henan province in China and Ledong in Hainan province in China in 2017.The second genetic mapping population comprising 108 F6 recombinant inbred lines(RILs),developed by single-seed descent from the cross:(P178 × Lx9801),was planted in the experimental field for phenotyping at Xuchang in Henan province in China and Ledong in Hainan province in China in 2017.Disease scores were recorded at 20 days post-pollination.All plants in the plots were scored visually for SCR severity using a scale from 1(most resistant phenotype)to 9(most susceptible phenotype).A significant difference was detected between two resistance donors(CML496 and P178)and susceptible parent line Lx9801.The parent lines CML496 and P178 were highly resistant to P.polysora with mean SCR score 1.5 across the two different environments,while Lx9801 was highly susceptible to P.polysora with mean SCR score 7.5 across those environments.2.The genotypes of the two populations were detected by 3588 and 4051 polymorphic SNP markers,and two genetic maps were constructed,which represented 1049 and 1424 unique bins respectively.The first genetic map spanned a total length of 1840.43 c M with an average distance of 1.75 c M between markers.The second genetic map spanned a total length of 1936.35 c M with an average distance of 1.36 c M between markers.3.The QTL analysis of the two populations was carried out by using the composite interval mapping(CIM)method.One major QTL(q SCRCML496)was detected across all two environments,which was located on chromosome 10,from resistance parent CML496.And one major QTL(q SCRP178)was detected across all two environments,which was located on chromosome 10,from resistance parent P178.All two QTLs were maped into a resistace gene cluter located on chromosome 10 S.4.Genome sequences from CML496,which releated to NBS-LRR genes,were captured and sequenced using Pac Bio.258 NBS-LRR contigs were obtained from CANU assembly.192 NBS-LRR genes were annotated from MAKER-P with a strict filtration.The analysis of the QTL mapping interval indicated that a total of 8 complete CNL genes from 192 protein coding genes could be used as candidate genes for next-stage single gene isolation and functional verification.In summary,we mapped two major QTL resistace to SCR using genetic maps containing high-density SNP markers rapidly,and obtained 8 CNL(CC-NBS-LRR)genes could be used as candidate genes from resistance donor CML496 using Renseq in just two years.And this can provide a reference for resistance gene cloning and functional analysis to SCR.