Analysis Genetic Effects And QTL Mapping Of Silk-cut In Maize

The ratio of germination and seedling was effected badly due to silk-cut, and thequality of commercial maize was impacted greatly after infection by epiphyte. Inbreedline 08-641 with the agronomy characters of high combining ability,big ear,multipleresist and wide adaptability, which was combinated abort 20 new maize varietiesauthorized by province or nation, has become main inbreed lines in southwestchina, especially in SiChuan province. As a result of harm by Silk-cut, the germinationrate of F1 combinated by 08-641 was relatively low. The incidence of the disease achieved30-40% for F1 combineted by 08-641 in northwest china, so its implication was impactedin a certain extent. Some genetic studies were developed in order to investigatethe genetic basis of the character and make preparation for the studyafterwards. In this study, inheritance of silk-cut of the crossR08×975-12(Zea mays L.) was detected by applying the major gene pluspoly-gene model of quantitative traits to a joint analysis ofmulti-generations (P₁, P₂, F₁, B_1:2, B_2:2 and F_2:4). And silk-cut QTL of maize weredetected by CIM method, using F₂ population and F_2:4 family.1. The results indicated that silk-cut in the cross R08×975-12 wascontrolled by one major gene with additive major gene effects plus polygenewith additive-dominance effects(the D-2 model). Genetic variance values ofthe major gene in B_1:2, B_2:2 and F_2:3 populations were estimated as 201.4525,31.9877 and 31.9877, while those of polygene were 11.0397 and 81.1362,respectively. And the additive effects values of major geneand polygene wereestimated as 11.3116 and -4.4719, while the dominance effects value ofpolygene was 10.8496. Heritability values of the major gene in B_1:2 and F_2:3populations were estimated as 21.56% and 81.31%, while those of polygene were4.46% and 54.68%, respectively.2. A genetic linkage map containing 115 SSR markers was constructed, whichcovered 2178.6cM totally, with an average of 18.9cM, in cross R08×Es40. Allthe markers were analyzed for the genetic segregation distortion, 19markers(at 0.05 level) were segregation distortion, and the ratio was 16.5%. By compared analyse, the SSR linkage map can be used for QTL mapping. Therelative order of SSR bin on the genetic linkage map was consistent with maizeGDB.In cross R08×Es40, 12 QTLs of silk-cut were detected by CIM method. TheseQTLs distributed on the chromosome 1,2,4,5 and 7, were named as qSC-1-1,qSC-1-2,qSC-1-3,qSC-2-1,qSC-2-2,qSC-3-1,qSC-4-1,qSC-4-2,qSC-4-3,qSC-5-1,qSC-7-1,qSC-7-2, respectively. Their position was 130.81,272.41,292.81,81.01,100.01,20.01,140.41,158.91,180.91, respectively, and their nearerlinkage marker was bnlg1564,umc1144,umc2189,umc1004,umc1003,bnlg2047,mmc0371,mmc0371,umc2280,umc1815,phi328175,phi328175,respectively.Two major QTLs, qSC-1-1 and qSC-3-1, were detected on the chromosome1 and 3, its contribution to phenotypic variations was 36.91% and 37.95%. Thecontributions to phenotypic variations for other 10 QTL varied from 4.22% to18.61%. The indication for the way of gene action was that among all the 12QTL, qSC-7-2 with overdominance effects, qSC-1-2,qSC-1-3 and qSC-2-2 withadditive effects, qSC-1-1,qSC-3-1 and qSC-7-1 with dominance, the others withpartial dominance effect on the character.3. A genetic-linkage map containing 86 SSR markers was constructed, whichcovered 1706.1cM totally, with an average of 19.8cM, in crossR08×99s2052-3-2-1. All the markers were analyzed for the genetic segregationdistortion, 12 markers(at 0.05 level) were segregation distortion, and theratio was 13.95%. By compared analyse, the SSR linkage map can be used forQTL mapping. The relative order of SSR bin on the genetic linkage map wasconsistent basically with maize GDB.In cross R08×99s2052-3-2-1, 4 QTLs of silk-cut were detected by CIMmethod. These QTLs distributed on the chromosome 2,3,5 and 6, were namedas qSC-2-1,qSC-3-1,qSC-5-1,qSC-6-1, respectively. Their position was 296.31,24.01,114.41,48.51, respectively, and their nearer linkage marker wasumc1080,bnlg1754,umc1019,umc1006, respectively.Two major QTLs, qSC-3-1 and qSC-5-1, were detected on the chromosome 3 and 5, its contribution to phenotypic variations was 39.42% and 43.11%. Thecontributions to phenotypic variations for other two QTL were 5.04% and 7.29%.The indication for the way of gene action was that among all the 4 QTL,qSC-3-1and qSC-5-1 with dominance effects, qSC-2-1 and qSC-6-1 with partialdominance effect on the character.4. QTL was detected on chromosome 3 in different combinations withdifferent genetic background. Its position were close, and the contributionrates were greater than 30%. The value and direction of gene action wereconsistent basically. All of these showed a major QTL which controlledcharacter of silk-cut for maize was true being on chromosome3. In addition,QTLs were also detected on chromosome3, 5.5. Silk-cut was abiotic disease which controlled by major gene plus minorgene by research of different genetic background and different methods. Thejoint segregation analysis and QTL method all have their superiority and theycould be confirmed and supplemented by each other.