| Studies on maize heterotic groups and patterns are very helpful to select elite inbreds and to raise the breeding efficiency. QTL mapping for important agronomic traits in maize is basic work to marker assistant selection (MAS). The objectives of this study were to classify heterotic groups of elite maize germplasm based on SSR markers and to analyze the tendencies of maize heterotic groups and patterns in our country over past decade; to map QTL and to estimate genetic effects for important agronomic traits by using the comosite interval mapping based on mixed model approaches with R1L population from a elite single cross Zong3 × 87-1. The main results were summarized as following:According to SSR marker genetic distance, the six inbreds selected from a set of American hybrids were clustered into one group with the topical lines, which may proved these inbreds might contain tropical germplasm at molecular level, which was named as Tem-tropic I heterotic group. At the Nei-Li distance of 0.92, 88 inbreds were clusted into seven heterotic groups, Reid, Lancaster, Zi330, TangSPT, Tem-trop I, E28 and others. Some changes of maize heterotic groups in our country had taken place during past decade. The major heterotic groups were Lancaster, Reid, Tang SPT, Zi330 and E28 in the early 1990s, while they were Reid, Tem-tropic I, Zi330, Tang SPT and Lancaster in the early 21st century.Based on classified heterotic group and the hybrid planting areas, it was observed that maize heterotic patterns in our country had changed certainly over the past decade. Firstly, with Tem-tropic I appeared in middle period of the 1990s, some new heterotic patterns, such as Reid × Tem-tropic I, Zi330 × Tem-tropic I, etc, become the major heterotic patterns at the beginning of 21st century. In the early and middle 1990's, the top five heterotic patterns were Reid × TangSPT, Zi330 × Lancaster, Lancaster × TangSPT, Lancaster × E28 and Reid × Zi330, while they were Reid × Tem-tropic I, Reid × Zi330, Reid × Tang SPT, Zi330 × Tem-tropic I and Lancaster × Tang SPT in early 21 century.Using composite interval mapping with mixed model, main genetic effect including epistasis and epistatic × environment interactions were analyzed under the same model in R1L population descended from a elite hybrid, Yuyu22. In all genetic effects influenced the plant height and related traits, additive and epistatic effects explained 47.84% to 58.02% and 15.45% to 20.51% of total phenotypic variation respectively, while additive × environment and epistatic × environment effects explained much less. The epistatic effects played an important role for the plant height as well as related traits, although the additive effects excelled the epistatic effects in explaining the phenotypic variation of plant height. Significant correlations were detected between the QTL controlling leaf number, upper node number and upper node length and QTL controlling plant height. Many pleitropic QTL were detected. Though every QTL of plant height could cause the plant height variation, they may not have the same genetic basis. 4. Regarding to the yield-related traits, additive and epistatic effects explained 20.28% to 49.07% and 13.33% to 30.53% of total phenotypic variation, respectively, while additive × environment and epistatic × environment interactions also explained much less. The epistatic effects also played an important role in theyield-related trait variations. Any single locus among most of epistatic QTL was not significant, which expressed little effect on trait variation. Main QTL and epistatic QTL expressed interaction with environment in a certain degree, while their contributions to trait variation were little.
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