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Trait Variation and QTL Mapping in Early-Season Maize Populations

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Title: Trait Variation and QTL Mapping in Early-Season Maize Populations
Author: Khanal, Raja
Department: Department of Plant Agriculture
Program: Plant Agriculture
Advisor: Lukens, Lewis
Abstract: Maize (Zea mays L.) inbred lines for hybrid breeding are usually developed within distinct heterotic groups. Breeders impose strong selection and maintain relatively small population sizes that are adapted to local environments, where the aim is to identify the desired recombinant types in the progeny. However, linkages between loci that control a trait may not permit breeders to obtain the desirable genetic recombination in these populations. It is hypothesized that different favorable and unfavorable alleles accumulate within the lines from different heterotic groups. In addition, within each inbred line, favourable alleles are linked with unfavourable alleles. Two early-season maize inbreds, CG60 (Iodent) and CG102 (Stiff Stalk), were used to develop a selfed recombinant inbred line (SRIL) and an intermated recombinant inbred line (IRIL) populations. Furthermore, individuals from within these populations were testcrossed with an inbred tester from the Lancaster Sure Crop heterotic group, to give rise to selfed SRIL testcross (SRIL-TC) and IRIL testcross (IRIL-TC) populations. The inbred and inbred-testcross populations were evaluated for trait variation and QTL mapping. The genetic variance was high in inbred populations (SRIL and IRIL) with transgressive segregation for flowering time and agronomic traits. However, genetic variances and correlation coefficients did not significantly differ between the inbred populations. Results suggested that pleiotropic genes were prevalent for these traits. In addition, linkages between the loci that control these traits were not common within parental genomes. Genetic linkage maps developed from the IRIL population were larger than those of the SRIL population. In the inbred-testcross populations (SRIL-TC and IRIL-TC) high means and high levels of trait variation were observed for all traits. The genetic variances and correlation coefficients of hybrid traits did not significantly differ between the SRIL-TC and IRIL-TC populations. Twenty five significant small to moderate QTL were detected, but only one, for grain moisture, was shared between inbred-testcross populations. Overall, the two inbred parents from different heterotic groups have many distinct alleles that contribute to traits. The recombinant inbred line populations had high means and variances for grain yield and related traits, which opens the possibility of utilizing these lines for hybrid breeding.
Date: 2011-10
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