| Drought is one of the most important limiting factors resulting in yield losses of maize in China. Therefore, basic research on drought tolerance (DT) is of great importance to breeding for drought tolerance. In this study, the DT genetic regions in maize were identified by a combination of genome- wide screening of DT introgression lines and QTL mapping using F2:3 families under water stress. The genetic base of important yield-related traits in maize was also investigated by phenotypic correlation analysis and QTL mapping under multi-environments. The main results were as follows.1. Identification of genetic regions related to DT at flowering time in maizeDT introgression populations from a cross of Qi319 (donor parent) and Huangzaosi (recurrent parent) were developed based on the performance of ASI (anthesis-silking interval) under the condition of serious water stress at flowering stage. The introgressed chromosomal segments were identified using SSR markers. The results revealed that the marker introgression percentage of DT populations significantly increased compared with the expected value (x2 test). And it was also found that the markers whose introgression percentage significantly increased concentrated on some chromosomal regions, e.g. 1.08, 2.07, 3.04, 4.01-4.04, 5.07, 6.05, 7.03, 9.04, 10.04. At last, twenty genetic regions related to DT for flowering traits were determined, which were distributed on chromosome 1 (one segment), chromosome 2 (two segments), chromosome 3 (one segment), chromosome 4 (five segments), chromosome 5 (three segments), chromosome 6 (one segment), chromosome 7 (two segments), chromosome 9 (three segments) and chromosome 10 (two segments), respectively. And most of these genetic regions covered the previously located QTL related to flowering traits. Some functional genes related to maize DT could be found within these genetic regions. It was also observed that the drought tolerance in terms of flowering traits for DT introgression populations was improved significantly after the DT selection, which confirmed that ASI could be used as screening criterion in genetic improvement of DT.2. Identification of main effect QTL and epistatic loci related to DT in maizeBased on investigation of phenotypes under two different water regimes and genotype identification of 230 F2:3 families, QTL with main effect and epistasis were dissected. The results revealed that the number of detected loci decreased significantly under water stress condition, implying that the different genetic mechanisms might exist under different water regimes. It was found that eight QTL related to DT at flowering stage based on the F2:3 families were mapped within the genetic regions related to DT identified based on DT introgression populations. These genetic regions related to DT included marker interval bnlg1957- bnlg1399 on chromosome 3, bnlg2305- bnlg1118 on chromosome 5, umc1339- bnlg1094- bnlg1579 and bnlg339- umc1408- bnlg2271 on chromosome 7 and phi062- umc1053 on chromosome 10. Based on the F2:3 families, four important QTL conferring heading date, pollen shed data, silking date and ASI related to DT at flowering stage were located within the same marker interval of phi062- umc1053 on chromosome 10 under stress condition, which could explain 13.8%, 17.3%, 19.6%, 10.9% of phenotypic variation of related traits, respectively.3. Phenotypic correlation analysis and concerned QTL mapping under multi-environmentsThe F2:3 population from the cross of Qi 319×Huangzaosi under three different environments was used to conduct phenotypic correlation analysis. The results revealed that ear traits and kernel traits might be important for yield genetic improvement. QTL with main effect and epistatic loci under three environments were also dissected. Same QTL were detected for different environments, e.g. QTL for days to anthesis within marker interval umc2405- bnlg572 on chromosome 4. The discovery of these loci would be helpful to marker assisted selection in maize. A number of epistatic loci were also revealed in this study, indicating that epistatic effect might also be important for maize breeding. |
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