An integrated approach to stabilising HFN in wheat: screens genes & understanding

The aim of this project is to improve stability of the Hagberg Falling Number (HFN), a major quality trait in wheat. HFN is currently sensitive to a number of environmental conditions that reduce the quality of grain and make it unsuitable for bread-making, resulting in severe financial losses to farmers: last year (2004) only 27% of the UK wheat crop grown for bread-making was of acceptable quality, with an estimated loss to farmers of £100 per acre of wheat grown. UK cultivars vary in their susceptibility to low HFN, partly due to the difficulty of applying conventional phenotypic screens to large populations of breeding selections, but some (eg. Option, Malacca) evidently carry adequate genetic resistance. Recommended List scores for HFN rely on the occurrence of appropriate weather conditions to trigger latent susceptibility or overhead irrigation to provoke pre-harvest sprouting (McVittie J & Draper S (1982) or irrigation of standing plots of winter wheat in order to assess varietal predisposition to pre-harvest sprouting. J. Natn. Inst. Bot. 16: 45-48). A key aim of this project is to furnish new tools and biological insights to enable breeders to identify new lines with stable HFN from the available pool of elite UK germplasm. The fact that existing resistant cultivars do not manifest problems with emergence in field sowings indicates that this aim is compatible with prompt stand establishment. Previous research by the applicants has shown that the two most important causes of high alpha-amylase levels in UK grain are pre-harvest sprouting (PHS) and pre-maturity alpha-amylase (PMA). PHS is the result of premature germination of grain in the ear, promoted in susceptible varieties by wet weather in the period between maturity and harvest. The consequent secretion of alpha-amylases into the starchy endosperm results in the deterioration in grain quality that is measured by the HFN test. PMA is less well defined, but is believed to result from inappropriate production of alpha-amylases by the aleurone layer in the crease region of the endosperm, late in grain development. Within the BBSRC financed objectives of this LINK project we intend to study the biochemical and molecular events in the wheat grain that are responsible for reduction of HFN during both PHS and PMA. Molecular genetic information from model species will be used to provide 'candidate genes' associated with germination potential/ endosperm development. These will be used for testing of function during seed development in relation to PHS/PMA. The characterisation of expression characteristics and genetic variation of candidate genes in existing germplasm, and the development of 'smart screens' and validated genetic markers will provide UK wheat breeders with resources to create improved varieties with more stable HFN. This project will address several components of the BBSRC strategic plan objectives for integrative biology and sustainable agriculture, including 'functional and comparative genomics', 'integrative biology-plant', 'transcriptomics', 'whole organism biology' and 'sustainable agriculture'. It will aim to provide a 'pipeline' for the delivery of information gained from studies in model species to tools for use to enhance breeding germplasm, a key recommendation of the recent BBSRC Crop Science Review.

Pre-Harvest Sprouting and associated increases in amylase production is the number one quality issue for UK wheat breeders. Sprouting results in massively reduced seed raw-materials quality that has downstream detrimental effects on post-harvest processing of grain. Detailed crop performance data over the past decade have shown that some UK cultivars perform adequately and show few symptoms of either PHA or PMA, whereas others are more susceptible; however, the complexity of the interaction between the wheat variety (genotype) and weather conditions (environment) that affect HFN has restricted the use of field-based screens for breeding of improved varieties. This project aims to bring a multidisciplinary approach to the problem. A key aim is the development of validated 'smart screens' through which PHS or PMA can be reliably induced in controlled environment conditions. These conditions will be used to characterise the performance of existing varieties to identify material with low and high resistance to PHS and PMA. The responses of the selected varieties to conditions that induce PHS or PMA will be characterised at biochemical and molecular levels to gain a deeper understanding of the biological processes involved. This will lead to the identification of genes that may be involved in the development of low HFN, which can be correlated with genetic loci identified through screening the mapping populations. Candidate genes will be identified from studies in model species, and used to analyse functionality in relation to PHS/PMA. This will include the analysis of variation present in UK varieties and mapping populations and in wheat TILLING populations, analysis of expression patterns in relation to PHS/PMA, and development of transgenic lines for proof of function. Existing populations, and new populations generated from selected parents, will be used for mapping genetic factors that contribute to HFN, which will be induced by overhead misting in the field and in controlled conditions. A total of 10 DH populations, segregating for PHS or PMA, will be used in QTL discovery and validation. Map locations of validated QTLs and candidate genes, will be used to identify those genes most likely to underly these traits and these will be specifically targeted in the generation of genome-specific, polymorphic PCR assays for use in forward breeding. The key deliverables will therefore be an improved knowledge of the biological processes involve in PHA and PMA, and reliable phenotypic screens and validated genetic markers that can be used to select for PHS and PMA resistance in wheat breeding programmes. This project was largely instigated by the UK wheat breeding industry, with encouragement from farming, milling and end-user groups, and these organisations have been closely involved in identifying the targets and deliverables of the programme. Most of the major UK wheat breeders will contribute significant intellectual and scientific resources to this project, and will be responsible for the construction and genotyping of mapping populations and the validation of molecular markers associated with resistance to PHS/PMA. It is anticipated that project management meetings, involving all partners and stakeholders, would be held at six-monthly intervals, with meetings between the researchers held at more frequent intervals. Plant breeders will be directly involved in mapping genes and validating markers in their own germplasm, and thus will begin using project outputs even before its conclusion. Results will be disseminated to the wider scientific and wheat breeding community through a website, presentations, technical articles and scientific papers.