Raising the ceiling on UK wheat yields / introgression and assessment of novel 'large-ear' CIMMYT germplasm into UK pre-breeding lines

Most major changes in UK wheats, such as the introduction of dwarfing genes (which reduced plant height, but increased the yield) have been introduced from wide crosses. Wide crosses can still be used to introduce new genes which allow further major changes to be made in UK wheats. The proposal presented here will introduce new genes conferring longer ear rachis (= axis of the ear) associated with improved ear fertility from Mexican wheats (from CIMMYT) which could facilitate a quantum leap in overall yield in UK wheats. The material to test this has already been produced. Specifically, we have created a population of lines from a cross between the Mexican 'big-ear' line and a productive (highly efficient at turning sunlight into sugar) UK adapted wheat, Rialto. In a preliminary study, we have shown rachis length to be positively correlated with ear fertility (and grain number per unit land area). This proposal asks for funds to look at why the Mexican wheat produces more grain for each ear than UK wheat and whether we can use the same genes to improve UK wheat yields. The programme works with UK plant breeders from CPB-Twyford Ltd to produce wheat pre-breeding lines containing these new genes from the Mexican material. For breeders to introduce novel traits into elite UK varieties, they must first know which genes are responsible for controlling the traits and how they work to cause differences between varieties. So, we will map the genes controlling ear fertility and in doing so develop genetic markers to facilitate their selection in breeding programmes. The weather and environmental conditions can vary considerably between different countries and genes that may be useful in some countries may not be in others. We plan to carry out physiological experiments which would identify why the Mexican wheat has more grains in each ear and how this might help improve wheat yield in the UK varieties. We will also carry out experiments to examine whether these genes influence other important determinants of yield at the crop level, such as ear number and grain weight. Crucially, there should be added benefits due to the high photosynthetic ability of Rialto combined with more fertile ears in the 'big-ear' line. We already have seed from the crosses which are needed to do this work, but need funding to understand how wheat controls the number of grains produced per ear. Our industrial partner will use their breeding expertise to make new lines suited to UK breeding, and we will help develop these lines and also use these lines to help us understand the genetics of how many grains are produced per ear. Using this combined approach we will then identify a pool of candidate genes which may directly influence this trait.

Under good management conditions in the UK, winter wheat is generally sink limited, with more photoassimilates produced during crop development than can be stored in the grain. This is largely due to limited grain number per ear. The International Center for Maize and Wheat Improvement (CIMMYT) has identified novel material with long ear rachis which has far higher potential grain number per ear than UK wheats. We have generated a doubled-haploid (DH) population (140 lines) of a cross between this CIMMYT novel ear material and the productive (high radiation-use efficiency, ratio of DM production to radiation interception) UK adapted wheat, Rialto. Crucially, there should be synergies between the high photosynthetic capacity in Rialto and improved ear fertility in the novel CIMMYT line. This research proposal presents an integrated approach using developmental, physiological and molecular genetic evaluation of lines from this cross to begin to understand the basis of this trait at all three levels. This will be coupled with the introgression of the 'long ear' phenotype into the CPB-Twyford UK wheat breeding programme and analysis of individual back-cross lines of a DH in each of an elite winter wheat and spring wheat UK background. We have shown that grains per square metre has had the highest phenotypic correlation with grain yield and contributed most to its genetic gain in modern UK wheat varieties in recent years. In a preliminary study, we have shown a positive correlation between both rachis length and spikelets/ear; and spikelets/ear and grains per square metre, in the DH lines. The developmental and physiological aspects of this proposal focus on understanding the biological processes determining fertile florets/ear at anthesis, concentrating on the biology of the plant during spikelet primordia production up to terminal spikelet and fertile floret survival up to anthesis. Specific objectives are to: (1) develop a detailed genetic map for the DH population and perform QTL analysis on trait data, (2) introduce the 'long ear' phenotype into UK pre-breeding and breeding lines through a back-crossing programme to each of an elite winter wheat and spring wheat variety (CPB-Twyford Ltd). We will then (3) use the DH population to identify the developmental and physiological basis of the novel ear fertility trait and (4) use specific DH lines to identify candidate genes for the novel ear phenotype using wheat microarrays. Finally we will (5) investigate the relationship between ear fertility and grain yield in the DH population. These objectives will be pursued through the combined expertise of the research team and CBP-Tywford Ltd, who will provide significant financial assistance through the back-crossing programme to evaluate and introgress these genes into UK varieties. Material from this backcrossing programme will be made available to the research team to pursue initial results obtained in the DH population and the research team will be directly involved in the back-crossing programme through marker-assisted selection in later generations. This integration between the research and plant breeding teams represents a powerful linkage from fundamental science to the generation of pre-breeding lines, facilitating the elucidation of this trait. The research proposed is novel in that it will improve understanding of the basic biological processes underpinning ear fertility in cereal plants and extend this to examine the generic effects within the unique ecological context of the most important UK cereal crop wheat.