Construction Of A Primary Molecular Genetic Linkage Map In Cassava (Manihot Esculenta Crantz)

Cassava is the top three important tuber-root crops in the world, it supply staple food sources for more than 600 million people. Presently, cassava is known as one important bioenergy crop in the tropical area because of higher starch content with 28-35% in storage root and excellent tolerance to drought and barren soil. Large amount of cassava were grown in barren hill field with less manage and the yield potential have not yet been used. It is a chenllage research program that how to increase starch yield and resistance to abiotic stress, improve starch quality for industrial use to move up the intergrated value of cassava throughout molecular breeding.The molecular genetic map shows us the position relationship among important genes and markers in linkage group to be a crucial basis of the application of the molecular breeding technology in cassava. Construction of a high-density linkage map is an essential tool for genomics, and facilitating location of alleles, map-based cloning of genes, QTL mapping of important agronomical traits and molecular marker assist selection breeding. The accomplishment of genetic linkage map in cassava will be invaluable for directing genetic improvement of cassava variety as well as functional genomic studies.The experimental population with 210 lines from F1 hybrid between no-inbred parents SC6 and Mianbao was used make the primary molecular genetic linkage groups in cassava by SSR and AFLP analysis technology. The results are as following:Using more than 400 pair SSR primers mined by CIAT to test some of the individuals, 54 of them could produce polymorphic bands. There were 154 polymorphic alleles were discovered while screening the population by the 54 SSR primers, 2.54 polymorphic locus were amplified per SSR primers on average. Including of them, 81 of 154 polylmorphic fragments with 59.3% proportion showed the expected Mendelian segregation ratio by Chi-square Test.Twelve AFLP primer combinations of EcoRI and MSeI restricted enzyme have been used to screen the full population by ABI PRISMTM 377 DNA sequence analyzer. It's indicated that 352 polymorphic alleles have been detected. There is a veraging 29 polymorphic markers per primer combination. By way of Chi-square Test, 204 of these highly polylmorphic fragments showed the expected Mendelian segregation ratio and the proportion was 57.95%.Combining the all diversitive SSR and AFLP markers in the population, a primary molecular genetic linkage map in cassava was set up. The map consist of 200 markers (39 SSR and 161 AFLP markers) in 23 linkage groups with a total length of 1329.89cM and an average interval of 6.65cM each marker. The size of the linkage groups is ranged from 6cM to 124cM and the number of marker located in linkage group is from 2 to 74.The average interval distance of marker varied from1.16(LG1) to 21.84(LG18).According to this linkage group, a total of 154 QTLs for starch content(SC), root yield(FY) and harvest index(HI) were located on the genetic linkage map with over 2.5 LOD value in the 3 yearly conditions, including 78 main effect QTLs with above 30% of phenotypic variance explained(PVE). There were 77 QTLs for SC within 69 main effect QTLs with PVE 31.11% to 50.68% , 39 QTLs for FY within 4 main effect QTLs with PVE 34.41% to 36.67% and 38 QTLs for HI within 5 main effect QTLs with PVE 30.26% to 44.51%.Comparing to the previous result of QTL analyse which had been getten in our laboratory, four QTLs has been testified which were qSCb-17-1,qFYc-17-1,qFYa-22-2 and qHIb-20-1 with PVE 11.21% to 34.41%.The dense, distribution of markers, probably broblem and use of the map have been discussed in the paper. This data and information could be integrated with the first genetic map by CIAT and construct a more useful fine consensus genetic map in cassava.