Construction Of Chromosome Single Segment Introgression Lines And Mapping QTL For Chilling Tolerance At Seedling Stage In Maize

Genetic background of chromosome single segment introgression lines (SSILs) is simpler than classical mapping populations, so SSILs are elite materials to identify and and fine map quantitative trait loci (QTL) for complex traits. Chilling is a kind of major meteorological disasters in maize, and some countries and regions are threatened by this damage. It seriously affects the yield of maize. Thus it is important to carry out genetic study on chilling tolerance in maize and to develope varieties with chilling tolerance by crop genetic improvement.In this study, CML343(as donor parent) and Huangzao4(as recurrent parent) was used to construct a set of chromosome single segment introgression lines (SSILs), and numbers of introgression segments and their backgroud recoverages of the SSILs were evaluated. This will establish a foundation for the study of stress resistance in maize. Meanwhile, a BC2RIL population constructed by CML343×Huangzao4was also constructed and employed to dissect QTLs for chilling tolerance at the seedling stage. Main results are listed as follows:1. The BC2RILs were genotyped with201pairs of polymorphic SSRs, then26lines which could cover almost the whole genome of CML343were selected to construct SSILs. About96.56%genomic region of HZ4could be covered by introgressed segments harbored by the26ILs with segments length ranging from5.25to475.20cM.2. After backcrossing for three generations and selfed for one time, in the BC6F2generation,67lines with higher background recoverages were developed from the26ILs. The201SSRs were employed to genotype the67ILs. The results showed that there were9lines with only one introgressed segments,17lines with two introgressed segments and12lines with three introgressed segments. A total of64lines have more than90.00%background recoverage and harbor less than12segments, and could cover79.21%genomic region of HZ4. In addition, another3lines were added to complement the rest of the genomic region (7.80%), which still need to be backcrossed in the future.3. Chilling tolerance of119BC2RILs was evaluated at the seedling stage. Eight tolerance indices (ratios of traits measured under stress conditions/traits measured under normal conditions) and leaf damage degree were used to detected QTLs underlying maize chilling tolerance. A total of34QTLs with9.00%-22.00%of phenotype variation explanation (PVE) were detected with the method of single marker analysis (SMA) in two environments. Of which, six major QTLs could control two or three traits. With the method of ICIM, totally23QTLs were detected with PVEs ranged from6.81%to35.89%. Three QTLs were detected to be associated with two or three traits, and one QTL was detected simultaneously in two environments. In comparison with the QTLs revealed by SMA and ICIM,13QTLs were detected by the both methods. Moreover,4pairwise non-QTL epistasis interactions were detected which controlled rTFW, rSL and rSWC.4. To sum up,33QTLs for chilling tolerance at seedling stage were detected under two chilling-treatment conditions. Of which,22QTLs and13QTLs were detected under constant and variable low temperature, respectively. Furthermore, major QTLs were mainly distributed in the QTL clusters on chr7and chr9, demonstrated that these genomic regions might play important role in maize seeding chilling resistance.These results revealed that chilling resistance at seedling stage is a quantitative trait and controlled by polygenes in maize. The QTLs detected in this study could be further used for dissection the genetic architecture and genetic improvement of maize seedling chilling tolerance. In addition, the SSILs constructed in this study are important materials for validation and fine-mapping of these QTLs.