15-IWYP: Molecular Dissection of Spike Yield Components in Wheat

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We face a major challenge in understanding the genetic architecture of yield potential in wheat. We propose a systematic genetic approach to identify potential developmental bottlenecks in the early stages of spike and grain development. We hypothesise that this approach will contribute to the identification of novel allelic variation that will deliver step-changes in wheat yield potential. Increasing wheat yields will require simultaneous improvements of both the 'source' and 'sink' and that the various yield components must be studied together to address the known negative correlations that exist between some of these traits (e.g. grain number and weight). However, a reductionist and systematic approach can be used as an initial step to understand the gene networks regulating each individual yield component. This knowledge can then be applied to assemble the best allelic combinations. This proposal is focused on the 'sink' side of the equation and specifically on the simultaneous increase of the number of grains per spike and the size of the individual grains. These yield components are mainly determined during a relatively narrow and well-defined window in the early stages of spike and carpel/grain development. We propose to focus on the critical early periods of spike and carpel/grain development, combine favourable alleles previously identified by our groups, and exploit exome sequenced tetraploid and hexaploid TILLING (Targeting Induced Local Lesions in Genomes) populations to identify novel allelic variants. The past wheat TILLING population will allow rapid evaluation of genes in null double-mutants, whereas the bread wheat population will complement this approach and allow deployment into elite bread wheat varieties.In this project we will identify and characterise a set of genes regulating grain number and weight, and develop novel allelic combinations to enhance overall spike yield in wheat. We have validated a set of both natural and novel induced allelic variants from the TILLING populations that affect specific spike yield components and have systematically developed the germplasm, techniques, and functional genomics resources required to address the proposed objectives. We will exploit emerging genomic advances and will work closely with breeders to rapidly introduce this variation into CIMMYT germplasm. The variation and allelic combinations generated within this project have not previously been utilised in traditional wheat breeding programmes and, therefore, represent an unprecedented opportunity to make significant progress in the genetic yield potential of wheat.The main direct outcomes expected from this research are: (1) Identification and characterisation (molecular, physiological and agronomic) of novel gene variants controlling wheat spike yield components (2) Creation of double and triple mutants targeting all homoeologs for the selected genes to overcome functional redundancy(3) Generation of adapted germplasm with new allelic combinations affecting complementary spike yield components