Stacking pairs of disease resistance genes in wheat populations using telocentric chromosomes

Resistance of wheat to diseases such as fusarium head blight (FHB) and leaf rust is more effective and durable when resistance genes are stacked. This study investigated whether pairs of disease resistance genes will become fixed at higher frequencies in subsequent generations when placed in the hemizygous condition using telocentric chromosomes. Three pairs of telocentric chromosomes were tested for their male and female transmission to predict the fixation rate of hemizygous chromosome arms using reciprocal testcrosses. Hemizygous arm transmission was about 50% through ovules and about 75% through pollen because of pollen certation. To test if a corresponding increase in disease resistance could be observed in populations utilizing telocentric chromosomes, three resistance gene pairs were analyzed separately in three populations. These pairs were Lr16/Lr34 and Lr22a/Lr52 for resistance to leaf rust and Fhb1/Qfhs.ifa-5A for FHB resistance. Each of these gene combinations was involved in a crossing and selection scheme that identified F(1) plants that were either dihybrid or double monotelodisomic (DMTD). For each resistance gene combination F(3) families were produced for phenotypic testing. The Lr16/Lr34 and Lr22a/Lr52 F(3) populations both showed a sharp increase in leaf rust resistance among families derived from DMTD F(1) plants compared to those from dihybrid F(1) plants. A smaller increased resistance was found in the FHB population. The increased frequency of resistance was attributed to pollen certation and zygotic selection against the ditelosomic and double ditelosomic conditions. We conclude that telocentric chromosomes are a viable breeding tool to fix gene stacks.