Identification of genetic factors contributing to heterosis in a hybrid from two elite maize inbred lines using molecular markers.

TLDR

Molecular markers are widely used to identify QTLs for agriculturally important traits, aiding both genetic understanding and breeding program design. This study mapped QTLs for seven major traits, including grain yield, in a B73 × Mo17 cross to investigate heterosis and genotype‑by‑environment interaction. Using 76 markers covering 90–95 % of the maize genome, the authors evaluated phenotypes on 3,168 plots across three states and compared single‑marker and interval‑mapping methods to locate QTLs. Both methods detected similar grain‑yield QTLs (except on chromosome 6), heterozygotes consistently outperformed homozygotes indicating overdominance, and grain yield correlated strongly with heterozygosity, while most QTLs showed little G × E interaction.

Abstract

Abstract The use of molecular markers to identify quantitative trait loci (QTLs) affecting agriculturally important traits has become a key approach in plant genetics-both for understanding the genetic basis of these traits and to help design novel plant improvement programs. In the study reported here, we mapped QTLs (and evaluated their phenotypic effects) associated with seven major traits (including grain yield) in a cross between two widely used elite maize inbred lines, B73 and Mo17, in order to explore two important phenomena in maize genetics-heterosis (hybrid vigor) and genotype-by-environment (G x E) interaction. We also compared two analytical approaches for identifying QTLs, the traditional single-marker method and the more recently described interval-mapping method. Phenotypic evaluations were made on 3168 plots (nearly 100,000 plants) grown in three states. Using 76 markers that represented 90-95% of the maize genome, both analytical methods showed virtually the same results in detecting QTLs affecting grain yield throughout the genome, except on chromosome 6. Fewer QTLs were detected for other quantitative traits measured. Whenever a QTL for grain yield was detected, the heterozygote had a higher phenotype than the respective homozygote (with only one exception) suggesting not only overdominance (or pseudooverdominance) but also that these detected QTLs play a significant role in heterosis. This conclusion was reinforced by a high correlation between grain yield and proportion of heterozygous markers. Although plant materials were grown and measured in six diverse environments (North Carolina, Iowa and Illinois) there was little evidence for G x E interaction for most QTLs.