Inter-morphotype hybridization in tall fescue ( Festuca arundinacea Schreb.): exploration of meiotic irregularities and potential for breeding

The Continental morphotype of tall fescue is one of the main forage and turf grass species. However, it suffers from summer drought, especially in dry and hot climates. On the other hand, the Mediterranean morphotype of tall fescue display summer dormancy. Hybridization of the two morphotypes seems to be an efficient way to introgress summer dormancy from Mediterranean morphotypes into elite cultivars of the Continental morphotype. In this study, we performed a series of reciprocal crosses producing F1 hybrids. Phenotyping revealed heterosis for plant height, fresh weight and dry matter yield, with hybrids generally outscoring parental genotypes. On the other hand, F1 hybrids had reduced fertility and lower seed set. This was a consequence of meiotic irregularities. Both parental morphotypes carry chromosome pairing regulators responsible for diploid-like behavior in meiosis. However, it is clear from this study that the regulators from the two morphotypes are not compatible. We observed high frequency of multivalent formation and homoeologous chromosome pairing in F1 hybrids. Molecular and cytogenetic analyses indicate high level of genome differentiation between both morphotypes. This might be caused either by massive genome reshuffling during the evolution or, most likely, by origination of the two morphotypes from different parental species. As such, introgression-form of breeding involving several rounds of backcrosses resulting in the restoration of chromosome pairing regulator (at least in some plants) appears to be the only way to achieve stability of the hybrid genomes and thus, wider utilization of genetically stable and fertile hybrid tall fescue for forage and turf.