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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?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.Peer reviewe

Simulated swards of perennial ryegrass (Lolium perenne) growing in 1-m$ soil blocks in the glasshouse were either well watered or deprived of water for 57 d and then rewatered. The first aim was to measure effects of drought on sugar (water-soluble carbohydrate) composition of laminae and sheaths of mature laminae, and bases and laminae of young (growing) leaves. The second aim was to use pulse labelling with "%CO # to follow the partitioning of recently-fixed assimilates, and the assembly and consumption of reserve sugars (fructans). Over the last 7 d of drought growth almost stopped, old leaves died faster than they were replaced, and total sugar (which had doubled in concentration during drought) was rapidly consumed. Leaf laminae had lower content of total sugars and of large fructan (DP 5) than did growing bases and sheaths. Drought greatly reduced the rate at which sugar was exported from the laminae to the sheaths and growing leaf bases, and the rate at which it was converted to fructan. Nevertheless, fructan accumulated over the first 50 d of drought. Rewatering did not result in depolymerization and remobilization of sugars that had been formed during the last 7 d of drought, but stimulated their further assembly into high-DP fructans. Our hypothesis, that accumulation of neo-kestose (a DP-3 fructan) in droughted laminae was a symptom of sugar remobilization just before death, was disproved. It is concluded that sugar reserves contribute to drought resistance only under extreme conditions. The specific role of fructan in dry environments might be to improve regrowth when drought is relieved, rather than to enhance growth during drought.

Androgenesis using amphidiploid cultivars of Festuca pratensis × Lolium multiflorum as parents, overcame earlier problems that gave rise to widespread plant sterility amongst androgenic Festulolium populations. Two Festuca pratensis × Lolium multiflorum (2n=4x=28) cultivars, Sulino and Felopa, were highly amenable to androgenesis and 10% of plants, including some novel androgenic genotypes, had sufficient fertility to produce progeny and further generations. The genomes of amphidiploid cultivars, which represent the F8 generation, were the result of considerable intergeneric chromosome recombination. Moreover, during cultivar development, natural and breeders’ selection pressures had led to the assembly of gene combinations that conferred good growth characters and fertility with the removal of putative deleterious gene combinations. Over 80% of the androgenic plants derived from the amphidiploid F. pratensis × L. multiflorum (2n=4x=28) had 14 chromosomes and were likely to be dihaploids with a single genome of Lolium and of Festuca. In contrast, hybrids of F. pratensis × L. multiflorum (2n=2x=14) found naturally are invariably sterile. Structural reorganization within the genomes of the androgenic Festulolium plants had restored fertility in genotypes expected to contain the haploid genome of Lolium and Festuca. This provided opportunities for their future incorporation in breeding programmes and the development of fertile diploid Lolium–Festuca hybrids. Amongst the androgenic plants, Festulolium genotypes were recovered that conferred excellent drought resistance or freezing tolerance and were thought to be highly suitable for entry into plant breeding programmes.

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Key words: Genomic in situ hybridization (GISH), physical mapping, Lolium/Festuca complex, stress resistance. Recent advances in cytogenetics of the Lolium/ Festuca complex provide new opportunities for understanding and manipulating physiological mechanisms

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