Dissecting drought- and cold-tolerance traits in the Lolium-Festuca complex by introgression mapping

Recent advances in the cytogenetics of the Lolium-Festuca complex provide new opportunities for understanding and manipulating complex physiological mechanisms such as drought and cold resistance. This paper describes breeding programmes involving hybrids between two species: L. multiflorum, which offers good early growth and high nutritive value, and F. arundinacea, which is more stress tolerant. The programmes are designed to allow a rapid recovery of the Lolium genome and to restrict numbers of recombinants derived from Festuca. Use of genomic in situ hybridization (GISH) and an isozyme marker demonstrates how gene complexes from any part of the Festuca genome can be introgressed into Lolium. This enables us to construct genotypes combining desirable traits of both Lolium and Festuca species. By introgressing different Festuca genes into Lolium, quantitative traits such as tolerance to drought and cold can be 'dissected' into their different components, to clarify their function. Festuca genes for stress tolerance can be located by genomic in situ hybridization (GISH) and assigned to regions of chromosome arms in Lolium. Two Lolium genotypes are described, in which genes for drought resistance transferred from the F. pratensis sub-genome of F. arundinacea onto chromosome 2 of Lolium. The two drought-resistant lines have the high water conductance of Festuca on their adaxial leaf surface and the low abaxial conductance of Lolium. The paper also describes how androgenesis of L. multiflorum x F. arundinacea hybrids has led to the selection and characterization of genotypes with coacclimation to drought and freezing stress, in some cases exceeding that in the Festuca parent.