Magnesium Increases Homoeologous Crossover Frequency During Meiosis in ( Gene) Mutant Wheat-Wild Relative Hybrids.

Wild relatives provide an important source of useful traits in wheat breeding. Wheat and wild relative hybrids have been widely used in breeding programs to introduce such traits into wheat. However, successful introgression is limited by the low frequency of homoeologous crossover (CO) between wheat and wild relative chromosomes. Hybrids between wheat carrying a 70 Mb deletion on chromosome 5B () and wild relatives, have been exploited to increase the level of homoeologous CO, allowing chromosome exchange between their chromosomes. In -rye hybrids, CO number increases from a mean of 1 CO to 7 COs per cell. CO number can be further increased up to a mean of 12 COs per cell in these hybrids by treating the plants with Hoagland solution. More recently, it was shown that the major meiotic crossover gene on chromosome 5B () within the 70 Mb deletion, was responsible for the restriction of homoeologous COs in wheat-wild relative hybrids, confirming the phenotype as a complete deletion mutant (. In this study, we have identified the particular Hoagland solution constituent responsible for the increased chiasma frequency in mutant-rye hybrids and extended the analysis to TILLING and CRISPR mutant- hybrids. Chiasma frequency at meiotic metaphase I, in the absence of each Hoagland solution macronutrient (NH HPO, KNO, Ca (NO)2·4HO or Mg SO·7HO) was analyzed. A significant decrease in homoeologous CO frequency was observed when the Mg ion was absent. A significant increase of homoeologous CO frequency was observed in all analyzed hybrids, when plants were irrigated with a 1 mM Mg solution. These observations suggest a role for magnesium supplementation in improving the success of genetic material introgression from wild relatives into wheat.