The Correspondence Relationship Between 11 Linkage Groups And Chromosomes In Cassava Genetic Map

Manihot esculenta Crantz belongs to the family Euphorbiaceae,which is widely cultivated in tropical areas.Researchers have constructed 15 cassava genetic maps by using a wide varieties of molecular markers,but the corresponding relationships between linkage groups and chromosomes have not been completely determined.In previous research,our group has integrated some linkage groups with its corresponding chromosome,which was constructed by Chen et al.（2010）,Sraphet et al.（2011）and Rabbi et al.（2012）,while the rest linkage groups and their corresponding karyotypes remained unknown.Therefore,we used fluorescence in situ PCR to locate 20 markers from two genetic maps of cassava physically,followed by integrating the karyotype and linkage groups for where these markers from.The aim was to reveal the one-to-one correspondence between linkage groups and chromosomes in the genetic maps of Chen et al.（201 0）and Sraphet et al.（2011）.This research will establish foundation to construct of cassava molecular cytogenetic map,and provide the cytogenetic basis for the selection breeding,germplasm resource identification,comparative genomic science of cassava.The main results of this study were as follows:（1）Based on the cassava genetic map of Sraphet et al.（2011）,we used IS-PCR to locate the following markers:SSRY268 and SSRY313 at the two ends of the LG1,SSRY210 and SSRY219 at the two ends of the LG2,SSRY291 and SSRY182 at the two ends of the LG5,SSRY314 and SSRY104 at two ends of the LG6,SSRY61 and SSRY81 at two ends of the LG 10,SSRY200 and SSRY59 at two ends of the LG11,SSRY91 and SSRY276 at two ends of the LG 12,NS781 and NS40 at two ends of the LG 15 were located on the chromosome of SC6.The results indicated that the above 16 genetic markers were sequentially located on the short arm and long arm of the chromosome No.1,No.4,No.14,No.9,No.11,No.10,No.15,No.16,the percentage distance from the amplification site to the centromere were 87.46 and 78.22,81.16 and 56.33,46.50 and 58.30,50.41 and 52.49,15.02 and 34.91,72.62 and 52.73,42.65 and 75.55,60.39 and 68.32 one by one.（2）Based on the cassava genetic map of Chen et al.（2010）,we used IS-PCR to locate the following markers:EST5 and NS 10 at the same side of the LG8,marker M29E17 at the LG 10,marker EST68 at the LG 17 were located on the chromosome of SC6.The results indicated that the above 4 genetic markers were sequentially located on the short arm of chromosome 14,the long arm of chromosome 15,and the long arm of chromosome 2.The percentage distance from the amplification site to the centromere was 62.90 and 61.38,6.91,and 44.47,respectively.（3）In this study,we used IS-PCR and karyotype analysis to reveal the corresponding relationships between 11 linkage groups and 9 chromosomes.For the genetic map of Sraphet et al.（2011）,LG1,LG2,LG5,LG6,LG 10,LG11,LG 15 were determined as cassava chromosome of No.1,No.4,No.14,No.9,No.11,No.10,No.15,No.16,respectivly;For the genetic map of Chen et al.₂₀₁₀,the LG l,LG4,LG 14,LG9 were determined as cassava chromosome of No.14,No.15,No.2,respectivly.Moreover,our reseach showed that some linkage groups derived from different genetic maps were dertermined to be same corresponding chromosomes.Two markers of the 5th linkage group from Sraphet et al.（2011）and two markers of the linkage group 8 from the genetic map of Chen et al.（2010）were mapped to the cassava chromosome 14 by in situ PCR.The order from the top of the short arm of the chromosome to the end of the long arm were EST5,NS 10,SSRY291,SSRY182.It was indicated that the linkage group 5 and the linkage group 8 correspond to the same chromosome,and the genetic markers of the two linkage groups may be partially identical,and some complementary;Similarly,the genetic markers mapped to chromosome 15 were also derived from the above two genetic maps,and the order of the three markers from the top of the short arm to the end of the long arm was SSRY91,M29E17,and SSRY276.（4）Combined the results in this study and previous researches,we clarified the correspondence between the 24 linkage groups and 15 chromosomes,and defined the positional relationship of the markers on the linkage groups in different genetic maps.In addition,we found that the linkage group derived from different genetic maps correspond to the same chromosomes.The LG7 from the genetic map of Sraphet et al.（2011）and the LG17 from the genetic map of Chen et al.（2010）were corresponding to cassava chromosome 2;similarly,the two genetic maps of LG9.and the LG2 and LG 16,LG11 and LG 18.LG 10 and LG 15,LG 12 and LG 10 were corresponding to the cassava chromosomes of 3,4,1 0,11 and 15 respectively;the LG6 derived from the genetic map of Sraphet et al.（2011）and the LG9 from the genetic map of Rabbi et al.（2012）were corresponding to cassava chromosome 9.