Mapping Of Quantitative Trait Loci Coffered Resistance To Brown Spot In Tobacco (Nicotiana Tabacum L.)

Molecular marker-assisted breeding (MAS) is becoming more and more important and useful tool in modern crop improvement. Accelerate to select target traits using the linkage between target gene and molecular markers. Howerver, the MAS used in cultivar tobacco is in its infant as there is little useful and stable molecular markers. Firstly, the genome of tobacco has not been completely sequenced. Secondly, the genetic distance among tobacco is higher than other crops, especially for the flue-cured tobacco, it is difficult to develop markers in the same type. Tobacco brown spot disease is one of the most important disease.One purpose of breeding is select several species that resistant the disease.MAS is needed to select those species because this disease, affected by the environment is difficult to investigate by traditional method.The purpose of this study is to construct a genetic map between two flue-cured tobaccos, jingyehuang and changbohuang using SSR makers, to find loci which relate to tobacco brown spot disease. Results of our research as follows:(1) molecular linkage groups of tobacco by SSR markersSSR makers are developed from genome of tobacco of the TGI(http://www.tobaccogenome.org). All the makers are selected by changbohuang, jingyehuang and F1(changbohuangxjingyehuang) to find the polymorphic makers.In this research,mroe than 2000 SSR markers are developed from TGI data and 212 polymorphic(about 10% of the SSR makers) makers can be selected. The F2 population is used as mapping population which contain 213 F2 plants.All the data of 212 SSR makers in F2 population were used to construct a molecular genetic map by MapMaker/Exp3.0. Finally, we got 24 linkage groups which included 181 SSR markers, and covered 2022 cM with an average distance of 11.2cM.(2) QTL of brown spot disease A.alternata attract tobacco leaves when leaves are beginning to mature. The brown spot disease index of F2 plants can be got when the disease index of G140 that used as susceptible control arrive 75%.Using method of composite interval mapping in WinQTLCart2.5 to detect QTL of tobacco brown spot disease index. In our research 3 QTL in 3 linkage groups are detected for brown spot disease index, the contribution of these QTL are from 4.8%to 13.77%.(3)clustering of several tobacco species by random SSR makers and the makers which linked with resistant brown spot genesThe random SSR makers and the makers, near the 3 resistant QTLs,were used to analysis.NTSYSpc2.1 is used to cluster for these species.The cluster results show:Four group are clustered when similar index is 0.44 in 33 varities. beinhart-1000 and jingyehuang were clustered in a large group, N.suaveolens in an unique group. The other two groups:one for CV series, another include changbohuang, G140, NC82 and other susceptible varieties. cluster results show that the makers, near the QTLs, can cluster the species are resistant or susceptive while the radom makers can't do that. So this research's result can reflect the QTL of tobacco brown spot disease index is accuracy.