QTL Analysis Of Drought Tolerance At Seedling Stage Based On Introgression Lines And F_2:3 Families Of Maize

In China, maize is the second largest grain crop. Drought is the most serious abiotic stress to affect the growth and development and thus yield of maize, which occurs frequently in the main growing areas. The growth of maize at seedling stage impacts on the whole process of growth. Therefore, to understand genetic mechanisms of drought tolerance at seedling stage, e.g. quantitative trait loci (QTL) location by the use of molecular markers, will provide bases for maize breeding, especially marker-assisted selection.Previously, selective introgression lines were obtained from backcrosses of 235 inbred lines and an inbred line"Huangzaosi"(recurrent line). Selective BC₂F₁ and BC₃F₁ of Huangzaosi×Ye478 were used in the present study. Meanwhile, an F_2:3 population of Huangzaosi×Ye478 was used in QTL analysis for some important traits including drought tolerance at seedling stage. The main results are as follows.1. The 235 F_2:3 families of Huangzaosi×Ye478 were used in construction of genetic linkage map including 137 SSR markers. The map covered 2849.9 cM, with the average genetic distance of 20.8 cM. Statistical analysis indicated that among all the SSR markers genotyped the frequency of the distortion was 33.3%."Hot spots"of distortion concentrated on chromosome 3, 7, 8, 9 and 10.2. Considering four traits including plant height, relative water content (RWC), biomass above the ground and chlorophyll content, Ye478 was less drought tolerant than Huangzaosi. QTL analysis indicated that the QTLs for plant height had the feature of time-specific expression. The QTLs associated with plant height were found in chromosome 1 (umc1009 - umc1331) and chromosome 2 (umc1845 - phi083), with the sources of alleles from Huangzaosi and Ye478, respectively. Two QTLs for plant height , i.e. bnlg1643-bnlg1597 (1.11) and umc1539-bnlg1047 (3.08), were near QTL found in previous studies. One QTL on chromosome 10 was a newly detected in this study. Most of QTLs had genetic effects of part dominance (PD) and over-dominance (OD). In additioin, a QTL was found to affect plant height, the fresh weight, and chlorophyll content.3. In three environments including Beijing, Xinjiang and Henan, the numbers of QTLs detected for plant architecture were 12, 10, and 11, respectively. Most of QTLs for plant height and ear height were detected simultaneously. The source of alleles of the QTLs for ear height mostly came from Huangzaosi. The source of alleles of the QTL for number of tassel branches mostly came from Ye 478. The number of QTLs for flowering-related traits were 12, 15 and 15 in the three environments, respectively, most with part dominance. The interval of nc030-umc2166 on chromosomes 3 was detected to relate to tasselling time, anthesis time and Silking time. The more alleles contributing to flowering-related traits from Ye478 were detected than from Huangzaosi Furthermore, 48 QTLs were found to associate with yield-related traits, mostly with genetic effects of part dominance (PD) and over-dominance (OD). The QTLs located in Chr1,2,8,10 in Flowering and Yield were the same loci with QTLs in the Seedling stage.4. Genotyping the selective BC₂F₁ and BC₃F₁ introgression lines by SSR markers indicated that introgressed fragments in BC₂F₁ were more than those of BC₃F₁, with the average number per BC₂F₁ line of 24.2 and the average number per BC₃F₁ line of 17.8. Totally 48 markers were detected significantly byχ² test in BC₂F₁ while 31 of these 48 markers were detected significantly in BC₃F₁. Chromsomal regions in the bins of 1.03 (phi109275), 2.03 (umc1845), 2.04 (phi083, umc2248), 10.02 (umc1152) and 10.03 (umc1053) which were detected significantly using these introgression lines coincided with the QTLs detected by the F_2:3 population mentioned above. The additive of QTLs in introgression liness in the population of Huangzaosi×Ye478 is different in different environments.