Genetic mapping with testcrossing associations and F2:3 populations reveals the importance of heterosis in chilling tolerance at maize seedling stage

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 tolerancerelated 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 F 2:3 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.Maize (Zea mays L.) is an important food, energy, forage and industrial crop. However, chilling (0-15 °C) has become a major environmental factor that limits maize production and its distribution. Chilling stress affects germination, seedling growth, early leaf development and overall maize crop growth and productivity 1 . In particular, maize seedlings are the most sensitive to chilling stress during the transition phase from heterotrophic to autotrophic growth 2 . Therefore, elucidating the mechanism of maize chilling tolerance at the seedling stage (3-leaf stage) will help to genetically improve this trait.Yield performance is usually used to evaluate stress tolerance at the reproductive stage, while at the seedling stage, it mainly relies on morphological-physiological traits. Physiological traits, such as photosynthetic performance 3-5 , tissue water content, and levels of abscisic acid (ABA) and antioxidants 3 , usually respond to low temperatures earlier than changes in morphological traits and are extensively used as indicators of chilling tolerance. Additionally, as a kind of compatible solute to increase the osmotic potential and stabilize macromolecular structure, soluble sugar content can also be a good index for stress tolerance evaluation 6 . At the morphological level, chilling stress causes decreased growth rates, leaf elongation and dry weights 2 . Chilling stress decreases root hydraulic conductance 7 and often results in water-stress symptoms. Root development in chilling-sensitive maize seedlings was found to be distinctly reduced under chilling stress, and the root-to-shoot ratio in chilling-sensitive inbred plants decreased under chilling stress conditions at the 2-to 3-leaf stage 8 . Because physiological t...

Genome-Wide Association Study of Maize Aboveground Dry Matter Accumulation at Seedling Stage

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MaizeMine: A Data Mining Warehouse for the Maize Genetics and Genomics Database

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