Prospects of genomic selection for disease resistances in winter wheat (Triticum aestivum L.)

Field: Agricultural and Biological Sciences (Life Sciences)

The aims of this study were to improve selection for FHB and STB resistances by (i) evaluating the effect of the recently described dwarfing locus Rht24 in comparison to the widely used Rht-D1 on FHB and STB resistances, plant height, and heading date for the first time, (ii) investigating the potential of the non-adapted QTL Fhb1 and Fhb5 for breeding semi-dwarf wheat, (iii) analyzing the prediction accuracy achieved by within- and among-family prediction comparing the models ridge regression-best linear unbiased prediction (RR-BLUP) and weighted RR-BLUP (wRRBLUP), and (iv) computing the advantage from genomic selection and determine the percentage of correctly selected top 10 % individuals for FHB and STB resistances.\nThe results of this study demonstrated that the most recently described gibberellic acid sensitive dwarfing gene Rht24 on chromosome 6A reduces plant height by 8.96 cm without adverse effects on FHB and STB resistances. Further, no association with heading date was observed. In contrast, Rht-D1b decreased FHB resistance by 10.05 percentage points. This work has further shown, that the resistance alleles of Fhb1 and Fhb5 reduced FHB severity by 6.54 and 11.33 percentage points, respectively, and that the non-adapted allele Fhb5b alone was able to counterbalance the negative impact of Rht-D1b on FHB resistance in a population consisting of eight bi-parental families segregating for these resistance loci. This indicates that in breeding programs the choice of semi-dwarfing and FHB resistance genes is of crucial importance where improvement of FHB resistance is a relevant breeding goal and breeders must select the appropriate dwarfing source that may confer resistance. In this study, furthermore, the potential of GS within and among families was investigated. The prediction accuracies evaluated within individual families were higher than those among families for all traits and differed between families and prediction constellations. The upweighting of significant markers by using the wRR-BLUP model was superior to the commonly used RR-BLUP model when large effect loci like Rht-D1 or Fhb5 were present. In this study, the genomic estimated breeding values (GEBVs) of 2,500 untested genotypes were calculated based on a partially related training population of 1,120 genotypes and the 10 % most resistant FHB and STB individuals were selected as well as a random sample under consideration of plant height. The best linear unbiased estimators (BLUES) of the selected genotypes were evaluated at four ecologically different locations relative to a randomly selected sample of genotypes. For FHB resistance, a genomic selection advantage of 10.62 percentage points relative to the random sample was achieved. However, GS improved resistance to STB only by 2.14 percentage points. The results of this study indicate that a rigorous selection of breeding parents based on GEBVs for high FHB resistance seems not to be sufficiently reliable as the percentage of correctly selected individuals of the observed 10 % top individuals for the whole selection population was only 19 %.\nIn summary, GS has shown to be a valuable tool to support the breeding progress for the complex inherited FHB resistance over short cycles and increased population sizes. Increased resistance to FHB in winter wheat could be achieved by that approach in combination with the choice of the appropriate dwarfing source and the potential use of the non-adapted QTL Fhb5.