Using novel genetic diversity for hybrid wheat pre-breeding
Lead Research Organisation:
University of Cambridge
Department Name: Plant Sciences
Abstract
Theme: Agriculture and Food Security
The steady increase in wheat yields over the past forty years is largely due to genetic improvements in breeders' elite inbred varieties. However, this rate of increase is less than for hybrid crops such as maize or sugar beet. Hybrids are generally more productive than inbred varieties of the same crops. An immediate switch to hybrid wheat could lead to estimated yield increases of 3-15% under ideal conditions, with even greater relative advantages under sub-optimal situations. Hybrids are believed to be more tolerant of environmental stresses and may show increased yield stability across locations and years. Hybrids would also generate greater income for plant breeders, leading to increased breeding activity and acceleration in yield increase.
Heterosis (hybrid vigour) occurs when a hybrid outperforms its two inbred parents, and is a crude function of heterozygosity. Hybrid breeding often uses 'heterotic pools': germplasm groupings based upon genetic similarities. Crosses between different pools will be more heterozygous than crosses within the same pool. Breeders work hard to identify or establish distinct heterotic pools, and then to drive them further apart, increasing heterozygosity and thus heterosis levels in subsequent hybrids.
Within BBSRC's Wheat Improvement Strategic Programme (WISP; BB/I002561/1), NIAB has developed thousands of pre-breeding lines in a winter (cv. Robigus) hexaploid wheat background, based on resynthesis and wide crossing. The KWS variety Robigus, itself a wild wheat derivative, is a key parental component in many elite UK lines. Resynthesis introduces diversity through crossing diploid Aegilops tauschii (DD) with tetraploid durum wheat (AABB). The resulting resynthesised wheat (also called SHW; AABBDD) can be used routinely in crosses with elite modern wheat varieties. A- and B-genome diversity has similarly been explored at NIAB through direct crosses between tetraploids and elite modern wheat varieties.
The project will be broken down into three broad areas:
1. Assess genetic diversity in pre-breeding germplasm and initiate the development of a heterotic pool based on NIAB's SHW- and tetraploid-derived Robigus material ('WISP lines'). Selections will be crossed to a KWS tester line to produce F1 hybrids. The same tester will also be crossed with Robigus-derived elite varieties. Both sets of hybrids will be compared in trials across Europe to evaluate the potential of using WISP lines in hybrid breeding.
2. Large ears carrying more potential grain sites are a common feature of exotic pre-breeding material eg WISP lines. This trait often disappears at high commercial planting rates. However, seeding rates will be lower in hybrid fields, which may lead to greater expression of the large ear trait. This hypothesis will be explored through agronomy trials at multiple locations to compare lines with contrasting ear types grown at different planting densities.
3. The importance of heterosis in the genetic control of key traits such as disease resistance and end-use quality remains unclear. RNAseq and other transcriptomic approaches will be used to assess the changes in gene expression for F1 hybrids relative to their inbred parental lines, grown in different situations.
This pre-breeding project encompasses genetics, transcriptomics, agronomy and marker-assisted selection, and will give a thorough grounding in all aspects of modern plant breeding.
This project will evaluate the potential of pre-breeding material in a commercial F1 hybrid development programme. It will test hypotheses about heterotic pool development, the manipulation of traits through agronomy, and gene expression in hybrids. The beneficiaries of the project will include:
1. Academic crop scientists
2. Private sector plant breeding companies
3. UK science base
4. The wider UK public and policy makers
5. Research scientists, including the candidate via training
The steady increase in wheat yields over the past forty years is largely due to genetic improvements in breeders' elite inbred varieties. However, this rate of increase is less than for hybrid crops such as maize or sugar beet. Hybrids are generally more productive than inbred varieties of the same crops. An immediate switch to hybrid wheat could lead to estimated yield increases of 3-15% under ideal conditions, with even greater relative advantages under sub-optimal situations. Hybrids are believed to be more tolerant of environmental stresses and may show increased yield stability across locations and years. Hybrids would also generate greater income for plant breeders, leading to increased breeding activity and acceleration in yield increase.
Heterosis (hybrid vigour) occurs when a hybrid outperforms its two inbred parents, and is a crude function of heterozygosity. Hybrid breeding often uses 'heterotic pools': germplasm groupings based upon genetic similarities. Crosses between different pools will be more heterozygous than crosses within the same pool. Breeders work hard to identify or establish distinct heterotic pools, and then to drive them further apart, increasing heterozygosity and thus heterosis levels in subsequent hybrids.
Within BBSRC's Wheat Improvement Strategic Programme (WISP; BB/I002561/1), NIAB has developed thousands of pre-breeding lines in a winter (cv. Robigus) hexaploid wheat background, based on resynthesis and wide crossing. The KWS variety Robigus, itself a wild wheat derivative, is a key parental component in many elite UK lines. Resynthesis introduces diversity through crossing diploid Aegilops tauschii (DD) with tetraploid durum wheat (AABB). The resulting resynthesised wheat (also called SHW; AABBDD) can be used routinely in crosses with elite modern wheat varieties. A- and B-genome diversity has similarly been explored at NIAB through direct crosses between tetraploids and elite modern wheat varieties.
The project will be broken down into three broad areas:
1. Assess genetic diversity in pre-breeding germplasm and initiate the development of a heterotic pool based on NIAB's SHW- and tetraploid-derived Robigus material ('WISP lines'). Selections will be crossed to a KWS tester line to produce F1 hybrids. The same tester will also be crossed with Robigus-derived elite varieties. Both sets of hybrids will be compared in trials across Europe to evaluate the potential of using WISP lines in hybrid breeding.
2. Large ears carrying more potential grain sites are a common feature of exotic pre-breeding material eg WISP lines. This trait often disappears at high commercial planting rates. However, seeding rates will be lower in hybrid fields, which may lead to greater expression of the large ear trait. This hypothesis will be explored through agronomy trials at multiple locations to compare lines with contrasting ear types grown at different planting densities.
3. The importance of heterosis in the genetic control of key traits such as disease resistance and end-use quality remains unclear. RNAseq and other transcriptomic approaches will be used to assess the changes in gene expression for F1 hybrids relative to their inbred parental lines, grown in different situations.
This pre-breeding project encompasses genetics, transcriptomics, agronomy and marker-assisted selection, and will give a thorough grounding in all aspects of modern plant breeding.
This project will evaluate the potential of pre-breeding material in a commercial F1 hybrid development programme. It will test hypotheses about heterotic pool development, the manipulation of traits through agronomy, and gene expression in hybrids. The beneficiaries of the project will include:
1. Academic crop scientists
2. Private sector plant breeding companies
3. UK science base
4. The wider UK public and policy makers
5. Research scientists, including the candidate via training
