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Using stable autopolyploids for double-hybrid breeding
Hybrids are created by crossing genetically different parents, resulting in a phenomenon called ‘hybrid vigour’ or heterosis, which can confer advantages over inbred parent lines in growth, resilience, and tolerance to environmental stresses. This is particularly true in autopolyploids, which can have up to four copies of each chromosome from four different parents. However, the double hybrid effect has never been used in breeding, as chromosome doubling to induce autopolyploidy can cause meiotic instability. While induced autopolyploids are meiotically unstable, this is not the case for established autopolyploids. The EU-funded SAMEY project will stabilise meiosis in induced autopolyploid Brassica rapa (Chinese cabbage). Stable autopolyploids will be used to produce double-hybrid lines, which will be evaluated for hybrid vigour for yield-related traits.
Hybrid breeding has been one of the biggest contributors to yield increase of the last century. Hybrids are individuals which have genetically different parents, which results in a “hybrid vigour” effect. This hybrid vigour effect can confer advantages over inbred parent lines in growth, yield, and resilience and tolerance to different types of environmental stresses, important for securing agricultural production in a changing climate. An even greater hybrid vigour effect is possible in autopolyploids, which can have up to four different copies of each chromosome, than in diploids, which have can only have up to two different copies of each chromosome. In effect, “double hybrids” can be made in autopolyploids, with up to four different parents contributing to hybrid vigour in a single individual.
However, to date the double hybrid effect has almost never been used for breeding. Most of our crops are not autopolyploids. We can induce autopolyploidy through chromosome doubling, but this causes meiotic instability, where multiple crossovers occur between the four chromosome copies during meiosis. This pairing disruption leads to potential loss of chromosomes and chromosome fragments essential for seed fertility and viability. Although induced autopolyploids are meiotically unstable, this is not the case for established autopolyploids. In the majority of established autopolyploids, a maximum of one crossover per two homologous chromosomes during meiosis is strictly enforced, thus achieving 100% pairing and correct segregation of chromosomes into daughter cells. I propose to stabilise meiosis in induced autopolyploid Brassica rapa (turnip, Chinese cabbage) by knock-out of crossover promoting genes, over-expression of crossover suppressing genes and selection of natural genetic variants. Stable autopolyploids will be used to produce double-hybrid lines, which will be evaluated for hybrid vigour for yield-related traits. |
