Final Report Summary - CAREBREED (Modern approaches for career development in small-grain cereal breeding) Adoption of molecular marker technologies coupled with the analysis of quantitative trait loci (QTL), and association genetics, has allowed regions of the wheat genome that regulate yield and other important agronomic traits to be identified. During our previous work we have identified over 45 QTL clusters that govern wheat yield in a wheat doubled haploid population from the cross Chinese Spring x SQ1 (Commission on Social Determinants of Health (CSDH)), with two on 7AL and 7BL that may confer high yield under a range of stressful conditions and exert major effects on yield in multiple trials over many years. To further dissect these apparently important regions of the wheat genome, we prepared sets of near-isogenic line (NIL)s targeting several of these QTL clusters for yield and related traits using the parental line SQ1 (an agronomically-acceptable spring wheat line) as the recurrent parent and four CSDH lines as donors. We then screened the progeny after five backcrosses and selfing with polymerase chain reaction (PCR)-based markers targeting 15 regions of the genome where major QTL clusters have previously been located for a range of agronomically-important traits: chromosomes 2BS (barc124), 2DL (gwm539 and gwm311), 3AS (gwm2), 4AL (wmc258), 4BL (gwm165 and dupw43), 4DL (gwm165), 5DL (wmc97), 6B (wmc398, wmc397, GS1 and gwm219), 6DS (cfd49) and 7BL (barc32). On arrival, we undertook the characterisation of BC5 selfed NIL plants (segregating for QTL++, QTL-- and heterozygotes) using molecular markers - the aim being to identify three QTL++ and three QTL-- NILs at each of 14 marker loci. Automated capillary fragment size analysis allowed the targeted number of QTL± NILs to be identified for most markers. In total 58 QTL++ and 71 QTL-- lines were identified across all 14 loci. Of these, 83 NILs identified to have either CS or SQ1 alleles for the selectable marker were phenotypically characterised in pot experiments under optimal conditions, measuring several traits expected to be associated with the QTLs and seeds collected for planned future work following the return of the fellow to his home institution. To confirm whether the QTL region of particular NILs had been retained or not, and to compare consistency in QTL expression between different (stress) environments, productivity traits (kernel weight per plant, kernel number per plant, mass of 1 000 grains, biomass per plant and harvest index) were measured in a set of 58 NILs, comprising at least two QTL-- and QTL++ plants for 11 marker loci, subjected to drought or ozone-induced oxidative stress. The yield QTL on 4AL (wmc258) that we have previously identified consistently controlled harvest index across treatments (control, drought and ozone treatments). Interestingly, another QTL determining yield (in non-stress environments) on 7B (barc32) that we have previously identified was associated not only with harvest index but also yield in non-stressful (control) environments. Also, locus gwm219 on chromosome 6BL was found to control kernel weight per plant, kernel number per plant, mass of 1000 grains and biomass per plant under control and stress treatments. While locus cfd49 on 6DS influenced all five productivity traits, but only in stress treatments. These two newly-identified loci could be important for breeding future wheat genotypes for combined tolerance to drought and ozone stress. A QTL on 5DL (wmc97), and two on 6B (gs1-sust and wmc397), were shown to influence productivity traits exclusively under drought treatment. Tolerance to stress (expressed as ratios of trait means: stress / non-stress) for kernel weight per plant (drought) and for harvest index (ozone) were associated with marker dupw43 (4BL). Targeted crosses for three QTLs, which increased grain yield via a CS segment at the QTL in the donor CSDH line, were successfully performed and F2 progeny grown and genotyped. Several homozygotes (QTL--/QTL--, QTL++/QTL--, QTL--/QTL++, QTL++/QTL++) were identified. The next stage will be to phenotype these lines to test the additive effects of the pyramided QTLs. Seed of QTL homozygotes together with seeds of some heterozygotes (to produce more homozygotes) were collected and disseminated between the project partners for further investigation. Our findings help understand how wheat grain yield is regulated in different environments; an essential step if we are to increase sustainable production of wheat in variable environments and ensure food security in a changing climate. As such, the project contributes to a core European scientific agenda. The germplasm resulting from the project will be further characterised at both the home and host institution during planned future studies, and made more widely available to the scientific community upon request. Related documents Final Report - CAREBREED (Modern approaches for career development in small-grain cereal breeding)
