INTERMEDIUM · Increasing the genetic variation of wheat germplasm by introgressing Thinopyrum intermedium chromosomes and chromosome segments

Increasing the genetic variation of wheat germplasm by introgressing Thinopyrum intermedium chromosomes and chromosome segments.

Wheat (Triticum aestivum L., ABD, 2n=6x=42), one of our most important food crops is facing such major challenges as climate change, and the narrowed genetic background of cultivated wheat cannot surmount such difficulties. The transfer of the genetic diversity from wild species provides an important strategy by which wheat can be adapted to the changing environment. Intermediate wheatgrass (Thinopyrum intermedium Barkworth & D.R. Dewey, J^rJ^vsSt, 2n=6x=42) is one of the most promising gene sources within the Triticeae. Its main advantages consist of resistance to various diseases (leaf rust, wheat streak mosaic virus, etc), tolerance of abiotic stresses (drought, high temperature, salinity) and perennial growth habit. The aim of the present work was to develop a new original strategy to exploit the full potential of the intermediate wheatgrass genome in wheat improvement by inducing genome wide introgressions in wheat-Th. intermedium hybrids and derivatives. The innovation in the present work is that it combines a highly effective crossing strategy with a high-throughput, low-cost screening procedure. The extremely abundant, cost-efficient and highly multiplexed Single Nucleotide Polymorphism (SNP) markers will be introduced into the wheat improvement procedure, which will open up new possibilities to speed up breeding. New technological advances, developed in a collaboration between the University of Nottingham, Bristol University and the company Affymetrix, are now enabling the high throughput detection of single chromosome segments (introgressions) from Th. Intermedium. This means we can transfer these tiny bits of genetic information from the wild relative into wheat on a large scale creating a step change in the search for new varieties of wheat that will cope with disease and climate change and help feed a growing population. Introgression of genetic variation from Th. intermedium into wheat occurs when the chromosomes of the two species recombine during gametogenesis in the interspecific F_1 hybrids (produced by pollinating hexaploid wheat with Th. intermedium). This results in the production of gametes which carry Th. intermedium/wheat recombinant chromosomes and in early generations, progeny may carry multiple introgressions. However, repeated backcrossing, in combination with selection, leads to the isolation of lines carrying a single Th. intermedium/wheat introgression in a wheat background. We have produced 36 BC_1, 72 BC_2 and 51 BC_3 plants with the help of 635 backcrosses. Selection procedures were being facilitated by the use of an Axiom 35k (Affymetrix) exome capture based SNP array. From the 2724 polymorphic SNPs identified, 643 were mapped on a preliminary genetic map composed of 165 BC_1, BC_2 and BC_3 plants. To support the SNP data analysis the presence of the wheatgrass introgressions have been confirmed by molecular cytogenetic techniques, i.e. genomic in situ hybridization (GISH) and fluorescent in situ hybridization (FISH). We have identified six different monosomic addition lines: 3J^r , 5J^r , 2J^vs, 5J^vs, 7St and 6St.J^r with the help of genetic mapping and GISH. Seven wheat-Th. Intermedium introgression lines were characterised by GISH and five were identified by FISH: 1A.St, 1D.St, 4A.St, 5A.J^vs, 6A.J^r. The good news for growers is that both the new germplasm and the information generated by this project will be made freely available (http://www.nottingham.ac.uk/wisp/wild-relative-gene-introgression/wild-relative-gene-introgression.aspx). That means plant breeders can use the germplasm to cross with their existing lines, while academics will be able to make use of it to understand the genetic basis of key traits in bread wheat.

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