Abstract
Maize seedlings are sensitive to low temperatures, and genetic mapping for chilling tolerance at the seedling stage with genetically diverse populations would facilitate the genetic improvement of this important trait. In this study, quantitative trait loci (QTL) mapping for four chilling tolerance-related traits at the seedling stage was conducted via a genome-wide association study (GWAS) with 338 testcrosses. A total of 32 significant loci and 36 stress tolerance-related candidate genes were identified, though none of them have been revealed by QTL mapping using maize inbred lines in previous reports. Moreover, expression of ten of the candidate genes was induced by chilling stress in a maize hybrid, though only a few of these genes were upregulated in its tolerant parent. These implied that heterosis might be involved in maize chilling tolerance. To further evaluate the importance of heterosis in chilling tolerance at the seedling stage, genetic mapping for chilling tolerance was conducted using an F2:3 population derived from the two inbred lines used for the gene expression assay. Of the seven QTL revealed, six loci showed partial dominance or over-dominance effects. Results from this study demonstrate that heterosis plays an important role in chilling tolerance in maize seedlings.
Highlights
Maize (Zea mays L.) is an important food, energy, forage and industrial crop
It is urgent to determine the genetic basis and dissect the genetic loci associated with heterosis for chilling tolerance in crops like maize and rice, where hybrids are extensively used
A genome-wide association studies (GWAS) with hybrids or testcrosses might identify genetic loci related to heterosis
Summary
Maize (Zea mays L.) is an important food, energy, forage and industrial crop. chilling (0–15 °C) has become a major environmental factor that limits maize production and its distribution. Rapid linkage disequilibrium decay makes maize an excellent model crop for genome-wide association studies (GWAS), and a number of significant loci for some chilling tolerance-related traits have been recently detected by GWAS at the seedling stage in maize inbred lines[4, 5, 14]. A number of significant loci and candidate genes for chilling tolerance were identified via GWAS at the seedling stage with a testcrossing association mapping panel; the QTLs were identified are completely different from those identified using maize inbred lines. Genetic mapping with an F2:3 population derived from the inbred lines used for the gene expression assay confirmed the importance of heterosis in maize chilling tolerance at the seedling stage. The results from this study provide new insights into the principles of heterosis in chilling tolerance in maize seedlings
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