Introgression-mapping of genes for drought resistance transferred from Festuca arundinacea var. glaucescens into Lolium multiflorum

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Abstract
Procedures for the transfer of genes for drought resistance from Festuca glaucescens (2n=4x=28) into Lolium multiflorum (2n=2x=14) are described. Following the initial hybridisation of a synthetic autotetraploid of L. multiflorum (2n=4x=28) with F. glaucescens, the F1 hybrid was backcrossed twice onto diploid L. multiflorum (2n=2x=14) to produce a diploid Lolium genotype with a single F. glaucescens introgression located distally on the nucleolar organiser region arm of chromosome 3. The transmission of F. glaucescens-derived amplified fragment length polymorphisms and a sequence-tagged-site (STS) marker was monitored throughout the breeding programme. Those genotypes of a mapping population of backcross 3 that survived combined severe drought and heat stress all contained the F. glaucescens-derived markers. The STS marker provided a prototype for a PCR-based system for high-throughput screening during cultivar development for the presence of the F. glaucescens-derived genes for drought resistance. The frequency of intergeneric recombination between L. multiflorum and F. glaucescens is described. During the initial stages of the breeding programme, preferential intraspecific chromosome pairing between Lolium homologues and Festuca homoeologues dominated with low frequencies of intergeneric chromosome associations. However, these increased in the backcross 1 due to the absence of opportunities for intraspecific chromosome pairing between homoeologous Festuca chromosomes following the loss of half of the Festuca chromosomes. Once transferred to Lolium, F. glaucescens sequences recombined with Lolium at high frequencies, thereby enabling the loss of potentially deleterious gene combinations that might reduce the forage quality of Lolium.