Advancing Harvest Index in Winter Wheat in High Biomass Backgrounds through Genomics Enabled Breeding

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Wheat is one of the three major staple cereal crops globally, with excess of 700m tonnes produced per year. Global demand for wheat is set to grow to 900m tonnes by 2050, and in order to meet that target, yields must increase by 1.6% per year, up from current annual increases of 1%. Research to improve biomass, particularly through the avenue of enhancing wheat photosynthesis may generate some yield increases, however this is unlikely to help hit yield targets unless the additional biomass generated is "useful biomass", or grain. Harvest index, (HI, grain dry matter (DM) yield / aboveground DM) is a measure of the ratio of useful biomass to non-useful biomass, and is a key component of yield. For winter wheat, HI values rarely exceed 0.55, and have not increased significantly since the 1990's, despite a theoretical limit as high as 0.65. A better understanding of the genetic basis of HI would allow for the improvement and stable expression of HI in higher biomass varieties, leading to a step change in genetic yield potential. There is significant evidence that yield potential is a sink limited trait, where carbon accumulation is limited by grain sink strength. Therefore improving grains per m2 is an important avenue for increasing the HI and yield potential of modern winter wheat. Fruiting efficiency is a measure of the number of grains set per unit of spike dry weight as anthesis, and is another trait of particular interest. This project is in collaboration with Drs Ed Byrne and Jacob Lage at KWS UK Ltd and will phenotype an association panel of elite KWS UK winter wheat doubled-haploid lines for grain yield, HI, 1000 grain weight and grains per m2; and grain partitioning and photosynthetic traits, including spike and stem-internode dry matter partitioning indices, fruiting efficiency (grains per unto spike DM at anthesis), canopy NDVI and leaf chlorophyll content (SPAD). The panel (150 lines), representing a stratified sampling across the KWS programme, will be genotyped. Marker-trait analysis will be performed via GWAS to identify markers for grain partitioning traits that can be used in breeding programs to select for high HI, high biomass genotypes.Wider germplasm including synthetic-derived and landrace-derived lines in the BBSRC Breders' Toolkit panel will also be screened (100 lines) and marker-trait analysis carried out to gain a better understanding of the range of potential loci. . The genetic and physiological basis of grain partitioning in the KWS panel will be investigated further with an RNAseq experiment on a subset of DH lines, in conjunction with spike hormone concentration analysis at booting.