With the rapidly growing human population and greater climate extremes, the importance of seed vigour is increasing with time because the vigour is closely associated with crop yield and resource use efficiency. Therefore, the issue of seed vigour is of central importance to agriculture and the seed industry but it is still poorly understood. Oilseed rape is the most cultivated and economically important species within the Brassica genus during the past 30 years. In 2017-2018 global production of rapeseed exceeded 74.71 making them the second most valuable source of vegetable oil and protein meal (40.12 Mt) in the world after soybean. Unfortunately, most of the double low (00) rapeseed cultivars are associated with agronomic problems, such as lower seed yield, poor germination, and reduced seedling growth rate. This study aimed to use an integrative approach to explore key genetic and metabolomic factors modulating seed germination and seedling vigour and the molecular link between these factors to breed new rapeseed varieties with superior germination and seedling growth.Seed germination and seedling vigour are quatitative traits determined by the interaction of hormonal, genetic and numerous environmental components. During the last decade, liquid chromatography-mass spectrometry (LC-MS), especially liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) has become the most widely used approach to plant hormone analysis. In addition, gene cloning has made it possible for oilseed breeders to develop genotypes/cultivars with high yield potential, improved oil content and oil quality and improved agronomical traits. In the first study, high-throughput UPLC-MS/MS hormone profiling of seeds and seedlings before and after germination in the high vigour (Express 617) and low vigour (1012-98) lines and their offspring was analyzed to identify key hormone components and their crosstalk causing poor germination and seedling development. This study is the first to report disruption of germination and seedling development in B. napus caused by the crosstalk of auxin-ABA and the corresponding regulators Bna.ARF10 and Bna.GH3.5.Quantitative trait locus (QTL) mapping is currently the most commonly used approach to dissect the genetic factors underlying complex traits. The goal of QTL mapping is to identify genomic regions associated with a specific complex phenotype by statistical analysis of the associations between genetic markers and phenotypic variation. In the second study, QTL mapping was used to identify quantitative trait loci related to germination, seedling vigour and seedling-regulated hormones in the same mapping population in the first study. A total of 13 QTL on nine chromosomes for germination and seedling-related traits at 7 and 14 days after sowing were detected. Forty-seven metabolic QTL on 15 chromosomes were identified for auxin, abscisic acid (ABA) and dihydrophaseic acid (DPA) at 5 and 12 DAS. Multitrait QTL hot spots contribute to our understanding of the genetics and metabolomics of germination and seeding vigour in B. napus, and represent potential targets to breed high-vigour cultivars. The innovative value of this work relies on the identification of key genetic and metabolomic components contributing to further development of robust markers for marker-assisted breeding of rapeseed varieties with superior seed vigour. With the astounding current developments in high-throughput genomics and metabolomic technologies, translation of the work results to new high-density genetic and metabolic maps to develop rapeseed varieties with hormonal balance and superior seed vigour.
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