Fusarium resistance in semi-dwarf wheat

Fusarium head blight (FHB) is a relevant disease of wheat and other small grain cereals almost worldwide. Infection with Fusarium head blight may lead to serious yield losses and quality problems due to the contamination with mycotoxins. Genetic resistance plays a key role in integrated disease management. Resistance of wheat to Fusarium head blight is a quantitative trait modulated by several to many genes and influenced by the environment. Recent research has shown that the widely employed semi-dwarf allele of wheat Rht-D1b is strongly associated with severely enhanced FHB susceptibility. Whether this association is due to a pleiotropic effect of the semi- dwarf allele itself or due to close linkage with the susceptible allele of another gene is currently unknown. In this project we will use a transgenic approach in order to clarify this question. We will transfer recombinant versions of the semi-dwarf allele Rht-D1b from wheat chromosome 4D into a tall wheat variety by particle bombardment and subsequent back-crossing and evaluate the progeny of the transgenic plants for stem length and for FHB response. These tests will clarify whether the association of the presence of the semi-dwarf alleles with increased FHB susceptibility is controlled by the genes themselves (pleiotropy) or not (then the association is due to linkage).

Fusarium head blight (FHB) is a relevant disease of wheat and other small grain cereals almost worldwide. Infection with FHB may lead to substantial yield losses and quality problems due to the contamination of the grains with mycotoxins. Genetic resistance plays a key role in integrated disease management. Resistance of wheat to FHB is a quantitative trait governed by several to many genes and modulated by the environment.Recent research has shown that the widely deployed semi-dwarf allele of wheat Rht-D1b, which is located on chromosome 4D, is associated with severely enhanced FHB susceptibility. Whether this association is due to a pleiotropic effect of the semi-dwarf allele Rht-D1b itself or due to coupling with the susceptible allele of another closely linked gene was unknown. In this project we used a transgenic approach in order to clarify this question. We transferred recombinant versions of the semi-dwarf allele Rht-D1b into wheat plants by particle bombardment. We then back-crossed the transgene into tall wheat cultivars and evaluated the progeny for stem length and for FHB response. Using transformation we generated experimental lines harboring the Rht-D1b allele, but at a random genome position dislocated from its native position on chromosome 4D. Both transgene expressing Rht-D1b and native Rht-D1b plants showed similarly increased FHB susceptibility and reduced plant height, when compared to sister lines with the tall allele at this gene. Our results therefore strongly point towards a pleiotropic effect of Rht-D1b on increased Fusarium head blight susceptibility, while the linkage hypothesis appears unlikely. This novel knowledge on the pleiotropic effects of Rht-D1b is crucial for wheat breeders and will have an impact on planning and designing future wheat breeding programs.