Development Of Chromosome Segment Introgression Lines And Elite Inbred Improvement By Molecular Marker Assisted Selection In Maize

The molecular marker-assisted selection (MAS) is an useful tool in crop breeding program and plays an important role in maize genetic improvement. The chromosome segment substitution lines (CSSLs) or chromosome segment introgression lines (CSILs) population which developed using MAS during backcross program can not only shorten the breeding period and raise the selecting efficiency, but also get the whole set of near-isogenic lines(NILs) with linked segment covering the whole genome which can be used as basic material for gene mapping, gene cloning and other theoretical and practical research.In this study, Zong3and87-1, parents of an elite maize hybrid Yuyu22, were used as recipient line, respectively, and HB522, an elite waxy inbred with disease resistance and lodging resisitence, was selected as donor line. Two set of link-up single segment introgression line (SSIL) populations were developed through3cycle advanced backcrossing.Foreground selection were conducted using the two SSR markers defined the introgressed segment and background selection of populations were screened using genome-wide SSR markers in each cycle of backcross. The size and number of introgressed segment, coverage of genome and phenotype were evaluated. QTL mapping for yield and yield-association traits were also performed. Additionally, R/3and waxy were used to improve inbred lines using three strategies of MAS, and background in these improved lines were screeded by genome-wide SSR markers, the effects of phenotype and combining ability caused by residual segment of donor were evaluated of improved lines and their hybrids. The results were shown as followling:1. The40lines were developed by83individuals derived from BC3F1of crossing87-1×HB522, and98lines were developed by122individuals derived from BC4F3of crossing Zong3×HB522, respectively. The population developed from87-1as recurrent parent was defined as87-1HBSSILs, similarly, the population developed from Zong3as recurrent parent was defined as Z3HBSSILs.2. A total of40donor genomic segments were introgressed into the87-1inbred. An average length of single introgressed segment was91.10cM on the basis of reference map IBM neighbor2005, ranged from0.03to342.86cM and covered a48.96%genome of87-1. A total of188donor segments were developed by the Z3HBSSILs. The number of these introgressed segments in each introgressed line varies from1to6, while the average number of them is1.92. The average length of introgressed segments was63.7cM, ranging from4.8cM to256cM on the basis of reference map IBM neighbor2005. The introgressed segment covered86.2%genome of maize.3. The QTL for grain yield and yield-association traits were identified using Z3HBSSIL population in Baoding and Zhangjiakou. A total of32QTL were detected across two environments, of which15for row number per ear (RNPE),6for kernel number per row (KPR),9for grain weight (GW) and2for weight per ear (WE), respectively. Each QTL explaining from4.57～33.06%,4.57～9.86%,4.24～19.27%and6.493～10.131%of phenotypic variance of RNPE, RNPE, KW and WE, respectively. The QTL around bnlg1083was identified in two traits across two locations.4. Three improved lines were developed based on three MAS strategies for Rf3and waxy gene selecting. Improved effect were evaluated and indicated that the improved line S-Mo17Rf3Rf3was completely fertile because of the introgression of Rf3gene. The total starch content of Z3-wxwx kernel was identical to that of in the Zong3kernel, but the amylopectin content of the former was significantly increased and its amylase content dramatically decreased because of the introgression of wx gene.5. Comparison of residual background among3improved lines derived from different MAS strategies indicated that17.9%donor chromosomal fragment was retained in87-1-wxwx which was developed by only selection of phenotype in BC3F1generation, and the residual segment distributed on all8chromosomes except chromosome1and10. While only about4%chromosomal residual was detected and distributed on minor region of chromsome7,8and9in Mo17Rf3Rf3which was developed by screening background using whole genome SSR markers in each generation. The background residual of Z3-wxwx line which was developed by background selection in BC3F1using MAS, was less than that of the line of87-1-wxwx, but more than that of Mo17Rf3Rf3. Phenotype were evaluated and revealed that the day to flowering (DTF) of S-Mo17Rf3Rf3was3days earlier than that of S-Mo17rf3rf3and its plant height (PH) was6.0cm lower than that of S Mo17rf3rf3. The PH and ear height (EH) of87-1-wxwx were both lower than that of87-1and its ear length (EL) and DTF was slightly shorter and3days earlier than that of87-1, respectively. The PH and EH of Z3-wxwx were taller than that of Z3and its DTF was3days later than that of Z3. The significant difference (P<0.05)) between87-1and87-1-wxwx was identified based on performance of multiple traits. Taken together, these results indicated that background selection by MAS could reduce the residual of non-target fragment of donor.6. Combining ability performed sililar between the MAS-derived lines and their corresponding recurrent lines. It was indicated that combining MAS and backcross could both improve the target traits and keep the combining ability of inbred line. However, there were still differences in few traits between the combinations of improved and unimproved inbred line with testers due to the interference of the residual background genome from the donor.