QTLs And Genetic Analysis Of The Major Characters Of Maize Inbred Lines Derived From Maize × Z. Mexicana Schard

Maize is an important crop with three functions as food, economic use and animal feed in China. Breeding and cultivating maiz hybrids of high quality to increase the yield plays an important role in solving the food security caused by the growth of population and the decrease of cultivated land in China. The breeding of elite maize hybrid usually relies on the utilization of good materials selected from the abundant germplasm resources. Wild Z. mays species is an important resource for maize genetic improvement. It has been an important research topic of genetic improvement of maize by transferring fine genes from wild species into maize in order to obtain stable pure lines of high yield, desirable quality, strong adversity disease and insect resistance. The genetic effects of main characters of maize have been subjected to intensive studies, but there was little report on the inbred lines from distant hybridization, which have particular functional characters such as tillering and prolificacy, and the results were not complehensive and consistant. Many important characters of maize, including plant height, yield and quality, are quantitative traits, which are controlled by polygene and meanwhile influenced by environmental factors. In recent years, a number of studies on QTL for these traits were carried out, while varied results, including the number of QTLs, location of QTLs on chromosome and segment, were obtained upon different materials and methods, as well as diverse environmental conditions. In addition, previous studies seldom involved tillering and prolificacy of maize, which were common in Gramineae and exhibited important function in cultivated maize. Therefore, new maize germplasm has been obtained through transferring genes from Z mexicana Schard by distant hybridization, the systematical genetic analysis and breeding-value validation, as well as the QTL locations and effects on the important agronomic traits, are of significant importance to improve maize breeding. This knowledge may provide a good foundation for molecular breeding in maize and maize prolificacy.1. In recent years, the genetic diversity of inbred lines from distant hybridization had been investigated to identify their morphological difference, however cytology and modern molecular genetic methods combined study were few. In this study, by using cultivated maize inbred-lines K169, K305, K363 and Zea mexicana schard as basic materials and by wide cross,19 new maize inbred lines with excellent incorporated genes from Z mexicana schard were selected by backcrossing and selfing. A systematical analysis of genetic difference of these 19 lines were performed by their agronomic characters, karyotype and SSR markers. The results were as follow:Among the 20 morphological characters of the new inbred-lines and their corresponding recurrent parent, inbred-lines 1154 and 1183 had the least characters of 8 that were significantly different,1164 and 11678 had the highest of character of,14, swhile other lines was from 9 to 13. Karyotype analysis showed that:(1) A noticable difference between inbred lines K169 and its derived lines were the Lt/St and the P.C.A%, with P.C.A%of the inbred-line K169 and 1193 being 0.1%, line 1183 and 11950.0%, line 11890.2%, line 11910.3%. The karyotype of line 1183 and 1195 were also different from K169. (2) Among the inbred-line K305 and its 12 derived lines, the karotype formula of the inbred-line 1171 and the K305 were 2n= 2x= 14 m (Sat)+6, which was different from the other 11 lines and K305. In addition, Lt/St was different between the inbred-line K305 and its derived 12 lines, and P.C.A%of the inbred-lines 1156,1157,1160,1162,1164,1167,1168 and K305 were also different; the karyotype of the derived lines and K305 were "2A" except inbred-line 1156,1157,1164, and 1168. (3)The karyotypic formulae of the inbred-line K363 and its derived lines 1154 were different. Lt/St and the P.C.A%of the inbred-line 1154 were 2.08 and 0.10, while those of the inbred-line K363 were 2.20 and 0.30. The results of SSR analysis indicated that the average value of genetic similarity coefficient of the inbred line K169 and its 5 derived lines was 0.5791, among which, the line 1193 had the highest one and its value reached 0.7043; the average value of genetic similarity coefficient of the inbred line K305 and its 12 derived lines was 0.6722, with line 1170 the highest being 0.7336; the average value of genetic similarity coefficient of the inbred line K363 and its 2 derived lines were 0.4259 and 0.2778, thus the genetic variations of these lines were higher compared with their corresponding recurrent parent. The results indicated that some excellent genes of Z mexicana schard had the potential to be transferred into those cultivated maize inbred-lines. These new maize germplasm would become new basic materials in maize breeding.2. It is of great significance to investigate the combining ability effect and the genetic characteristics of the main agronomic characters thus to identify the breeding potential value of the maize inbred-lines. In our study,133 hybrid combinations were obtained according to incomplete diallel cross mode using 7 elite maize inbred lines as female parents, and 19 inbred lines derived from distant hybridization as male parents. The combining ability and hereditary parameters of the main agronomic characters were analyzed, and genetic cluster analysis was performed on the 26 inbred lines. The results are as follows:(1) The analysis of combining ability effect indicated that the performance of the general combining ability was rather complicate among different inbred lines and their characters. Among 19 inbred lines derived from wide cross, line 1147 showed the highest positive GCA effect of tillering and prolificacy, line 1193 and 1169 relatively higher GCA effect of prolificacy, and line 1183 presented the highest positive GCA effect of yield per plant, ear diameter, kernels per row, and the following was line 1164,1157, and 1193. However, different combinations and their characters showed also different SCA effects. For example, combinations of K389×1162 and 156×1193 exhibited high SCA effect of yield per plant than other combinations, while the combinations of 156×1147 and K389×1164 had the positive maximum SCA for tiller number and ear number. (2) The analysis of genetic parameters indicated that the additive gene effect of tillering and prolificacy was much greater than that of non-additive gene effect, but the narrow heritability of the above characters was only 48.66%and 36.12%, respectively. Therefore, these characters should be selected at the late generations. The yield and its relative characters including plant height, leaf number, tassel and growth period were controlled by the additive gene effects. Hence, it was not appropriate to select them at the early generation. Since the additive gene effect of yield and its component characters was far more important than their non-additive gene effect, parents with higher GCA effect should be selected to conduct combination in breeding practice. Among the yield characters, the heritability of the ear diameter and ear rows was the highest (above 70%), while the ear length and barren ear tip length were relatively low (below 40%), and the other characters were in the middle of 50%-70%. Therefore, it is more effective to select ear diameter and ear rows in early generation. (3) The 19 inbred lines and 7 elite lines were clustered into 9 groups by genetic cluster analysis, of which the first group had 9 inbred lines including elite lines P178, 156 and inbred lines 1160; the second group had 5 inbred lines including elite line 698-3, K389 and inbred lines 1156; the third group included 3 inbred lines 1169,1191 and 1195; the fourth group included elite inbred lines 48-2 and R08; and the fifth group included 3 inbred lines 1154,1183 and 1189; while elite inbred line Zheng58 and lines 1153,1193 and 1147 were clustered into the sixth to the ninth groups respectively. The inbred lines of different groups had their own advantages, which might have directive significance in maize breeding. For examples, inbred line 1147 performed extremely large tillering and prolificacy, with higher plant height, and the GCA effect of those characters was greatest, so it was of more potential value probably in forage maize breeding. Line 1183 had such properties as large ear, more ear rows, high yield and high GCA effect etc, and it was a potential line for high yield breeding. Line 1153 was characterized by a short growth period and plant height, optimal plant-type and high kernel rate and performed higher GCA effect, therefore it could be applied on breeding for early, dwarf, and compact maize hybrids. The other new inbred lines, each with a distinct identity, could be improved and utilized appropriately based on the different breeding objectives.3. Investigation of the number, locations and genetic effects of the QTLs of the maize tillering and prolificacy and the other important agronomic traits may provide a good foundation for molecular breeding in maize and maize prolificacy. In current study,202 F2:3 family lines derived from a single cross between the inbred line K169 and 1147 were used as the mapping population. A maize genetic linkage map with 132 pairs of SSR markers was established, which covered 1979.6 cM of the whole genome with the average map distance of 15.0 cM. A total of 75 QTLs were identified in 15 major agronomy and yield traits, of which 7 QTLs influenced ear number, with each accounting for phenotypic variation ranged from 1.18%to 27.31%. QTL between markers phi96100 and bnlg1327 on the second chromosome explained phenotypic variation of 27.31%, thus it can be used to assist selection as a candidate molecular marker locus of maize prolificacy to increase the ear number. Other 14 QTLs contributed to plant height, ear height and leaf area, and 1-7 QTLs for single character were detected, with each QTL accounting for phenotypic variation from 1.71%to 12.98%; there were 11 QTLs influencing the branch traits with 3-8 QTLs of single character, and the effect of each QTL could explain 3.61%to 14.87%of phenotypic variation. Moreover,43 QTLs influenced the yield and other economic characters with 1-7 QTLs of a single character to explain 3.87%to 20.09%of phenotypic variation.